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151-592: Amyotrophic lateral sclerosis ( ALS ), also known as motor neurone disease ( MND ) or Lou Gehrig's disease ( LGD ) in the United States, is a rare, terminal neurodegenerative disorder that results in the progressive loss of both upper and lower motor neurons that normally control voluntary muscle contraction. ALS is the most common form of the motor neuron diseases . ALS often presents in its early stages with gradual muscle stiffness , twitches , weakness , and wasting . Motor neuron loss typically continues until

302-416: A N-methyl-d-aspartic acid receptor (NMDAR)-dependent LTP and long-term depression (LTD) due to the influx of calcium into the post-synaptic cell, which are the most analyzed forms of plasticity at excitatory synapses. Moreover, Ca2+/calmodulin (CaM)-dependent protein kinase II (CaMKII) is best recognized for its roles in the brain, particularly in the neocortex and hippocampal regions because it serves as

453-442: A polyglutamine (polyQ) tract . Diseases associated with such mutations are known as trinucleotide repeat disorders . Polyglutamine repeats typically cause dominant pathogenesis. Extra glutamine residues can acquire toxic properties through a variety of ways, including irregular protein folding and degradation pathways, altered subcellular localization, and abnormal interactions with other cellular proteins. PolyQ studies often use

604-474: A 20% change in the slope of the ALSFRS-R as being clinically meaningful, which is the most common threshold used to determine whether a new treatment is working in clinical trials. Difficulties with chewing and swallowing make eating very difficult ( dysphagia ) and increase the risk of choking or of aspirating food into the lungs. In later stages of the disorder, aspiration pneumonia can develop, and maintaining

755-490: A bulbar onset have a worse prognosis than limb-onset ALS; a population-based study found that bulbar-onset ALS patients had a median survival of 2.0 years and a 10-year survival rate of 3%, while limb-onset ALS patients had a median survival of 2.6 years and a 10-year survival rate of 13%. Those with respiratory-onset ALS had a shorter median survival of 1.4 years and 0% survival at 10 years. While astrophysicist Stephen Hawking lived for 55 more years following his diagnosis, his

906-464: A common disease spectrum (ALS–FTD) because of genetic, clinical, and pathological similarities. Genetically, repeat expansions in the C9orf72 gene account for about 40% of genetic ALS and 25% of genetic FTD. Cognitive and behavioral issues are associated with poorer prognosis as they may reduce adherence to medical advice, and deficits in empathy and social cognition which may increase caregiver burden. It

1057-430: A conflation of many criteria: clinical signs and symptoms, evaluations of the eye, electroencephalograms (EEG), and brain magnetic resonance imaging (MRI) results. The diagnosis provided by these results are corroborated by genetic and biochemical testing. No effective treatments were available to prevent the disease from being widespread before the past few years. In recent years, more models have been created to expedite

1208-428: A definitive diagnosis of PLS cannot be made until several years have passed. PLS has a better prognosis than classical ALS, as it progresses slower, results in less functional decline, does not affect the ability to breathe, and causes less severe weight loss than classical ALS. Progressive muscular atrophy (PMA) is another subtype that accounts for about 5% of the overall ALS category and affects lower motor neurons in

1359-443: A disease, ALS itself can be classified in a few different ways: by which part of the motor neurons are affected; by the parts of the body first affected; whether it is genetic; and the age at which it started. Each individual diagnosed with the condition will sit at a unique place at the intersection of these complex and overlapping subtypes, which presents a challenge to diagnosis, understanding, and prognosis. ALS can be classified by

1510-451: A fifth of consumed oxygen, and reactive oxygen species produced by oxidative metabolism are a major source of DNA damage in the brain . Damage to a cell's DNA is particularly harmful because DNA is the blueprint for protein production and unlike other molecules it cannot simply be replaced by re-synthesis. The vulnerability of post-mitotic neurons to DNA damage (such as oxidative lesions or certain types of DNA strand breaks), coupled with

1661-425: A fragment from a larger protein called amyloid precursor protein (APP), a transmembrane protein that penetrates through the neuron's membrane. APP appears to play roles in normal neuron growth, survival and post-injury repair. APP is cleaved into smaller fragments by enzymes such as gamma secretase and beta secretase . One of these fragments gives rise to fibrils of amyloid beta which can self-assemble into

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1812-409: A genetic cause, often linked to a family history of the disease , and these are known as familial ALS (hereditary). About half of these genetic cases are due to disease-causing variants in one of four specific genes . The diagnosis is based on a person's signs and symptoms , with testing conducted to rule out other potential causes. There is no known cure for ALS. The goal of treatment is to slow

1963-939: A gradual decline in the activities of repair mechanisms , could lead to accumulation of DNA damage with age and contribute to brain aging and neurodegeneration. DNA single-strand breaks are common and are associated with the neurodegenerative disease ataxia- oculomotor apraxia . Increased oxidative DNA damage in the brain is associated with Alzheimer's disease and Parkinson's disease . Defective DNA repair has been linked to neurodegenerative disorders such as Alzheimer's disease, amyotrophic lateral sclerosis , ataxia telangiectasia , Cockayne syndrome , Parkinson's disease and xeroderma pigmentosum . Axonal swelling, and axonal spheroids have been observed in many different neurodegenerative diseases. This suggests that defective axons are not only present in diseased neurons, but also that they may cause certain pathological insult due to accumulation of organelles. Axonal transport can be disrupted by

2114-423: A healthy weight can become a significant problem that may require the insertion of a feeding tube. As the diaphragm and intercostal muscles of the rib cage that support breathing weaken, measures of lung function such as vital capacity and inspiratory pressure diminish. In respiratory-onset ALS, this may occur before significant limb weakness is apparent. Individuals affected by the disorder may ultimately lose

2265-509: A homolog of phospholipase C β (PLCβ), an enzyme that cleaves PIP2. When ttx-7 mutants also had a mutant egl-8 gene, the defects caused by the faulty ttx-7 gene were largely reversed. These results suggest that PIP2 signaling establishes polarized localization of synaptic components in living neurons. Modulation of neurotransmitter release by G-protein-coupled receptors (GPCRs) is a prominent presynaptic mechanism for regulation of synaptic transmission . The activation of GPCRs located at

2416-426: A momentary alteration in the membrane's permeability. Additionally, transmitter-gated channels are comparatively less sensitive to the membrane potential than voltage-gated channels, which is why they are unable to generate self-amplifying excitement on their own. However, they result in graded variations in membrane potential due to local permeability, influenced by the amount and duration of neurotransmitter released at

2567-460: A number of ALS genes that encode for RNA-binding proteins. The first to be discovered was TDP-43 protein, a nuclear protein that aggregates in the cytoplasm of motor neurons in almost all cases of ALS; however, mutations in TARDBP , the gene that codes for TDP-43, are a rare cause of ALS. FUS codes for FUS, another RNA-binding protein with a similar function to TDP-43, which can cause ALS when mutated. It

2718-453: A number of other processes. CaMKII becomes active by autophosphorylating itself upon Ca2+/calmodulin binding. CaMKII is still active and phosphorylates itself even after Ca2+ is cleaved; as a result, the brain stores long-term memories using this mechanism. Nevertheless, when the CaMKII enzyme is dephosphorylated by a phosphatase enzyme, it becomes inactive, and memories are lost. Hence, CaMKII plays

2869-507: A physician suspects the person may have a myopathy rather than ALS, a muscle biopsy may be performed. A number of infectious diseases can sometimes cause ALS-like symptoms, including human immunodeficiency virus ( HIV ), human T-lymphotropic virus (HTLV), Lyme disease , and syphilis . Neurological disorders such as multiple sclerosis, post-polio syndrome , multifocal motor neuropathy , CIDP , spinal muscular atrophy , and spinal and bulbar muscular atrophy can also mimic certain aspects of

3020-461: A predominantly upper motor neuron phenotype. Emotional lability is a symptom in which patients cry, smile, yawn, or laugh, either in the absence of emotional stimuli, or when they are feeling the opposite emotion to that being expressed; it is experienced by about half of ALS patients and is more common in those with bulbar-onset ALS. While relatively benign relative to other symptoms, it can cause increased stigma and social isolation as people around

3171-459: A rapid worsening of symptoms. Sudden death or acute respiratory distress are uncommon. Access to palliative care is recommended from an early stage to explore options, ensure psychosocial support for the patient and caregivers, and to discuss advance healthcare directives . As with cancer staging , ALS has staging systems numbered between 1 and 4 that are used for research purposes in clinical trials. Two very similar staging systems emerged around

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3322-561: A reaction termed transamidation or crosslinking . Transglutaminase binding of these proteins and peptides make them clump together. The resulting structures are turned extremely resistant to chemical and mechanical disruption. Most relevant human neurodegenerative diseases share the property of having abnormal structures made up of proteins and peptides . Each of these neurodegenerative diseases have one (or several) specific main protein or peptide. In Alzheimer's disease , these are amyloid-beta and tau . In Parkinson's disease, it

3473-465: A role in this disease mechanism. Impaired axonal transport of alpha-synuclein may also lead to its accumulation in Lewy bodies. Experiments have revealed reduced transport rates of both wild-type and two familial Parkinson's disease-associated mutant alpha-synucleins through axons of cultured neurons. Membrane damage by alpha-synuclein could be another Parkinson's disease mechanism. The main known risk factor

3624-519: A similar time, the King's staging system and Milano-Torino (MiToS) functional staging. 2B: Involvement of the second region 4B: Need for non-invasive ventilation 4B: 30.3 months Providing individual patients with a precise prognosis is not currently possible, though research is underway to provide statistical models on the basis of prognostic factors including age at onset, progression rate, site of onset, and presence of frontotemporal dementia . Those with

3775-434: A single region for at least a year; they progress more slowly than classical ALS and are associated with longer survival. These regional variants of ALS can only be considered as a diagnosis should the initial symptoms fail to spread to other spinal cord regions for an extended period of time (at least 12 months). Flail arm syndrome is characterized by lower motor neuron damage affecting the arm muscles, typically starting with

3926-570: A small percentage of people have a much slower progression, on average people with ALS lose about 1 ALSFRS-R point per month. Brief periods of stabilization ("plateaus") and even small reversals in ALSFRS-R score are not uncommon, due to the fact the tool is subjective, can be affected by medication, and different forms of compensation for changes in function. However, it is rare (<1%) for these improvements to be large (i.e. greater than 4 ALSFRS-R points) or sustained (i.e. greater than 12 months). A survey-based study among clinicians showed that they rated

4077-475: A smaller family, older generations dying earlier of causes other than ALS, genetic non-paternity , and uncertainty over whether certain neuropsychiatric conditions (e.g. frontotemporal dementia , other forms of dementia , suicide, psychosis, schizophrenia ) should be considered significant when determining a family history. There have been calls in the research community to routinely counsel and test all diagnosed ALS patients for familial ALS, particularly as there

4228-399: A spectrum based on the degree of inflammation, a majority of patients experience early relapsing and remitting episodes of neuronal deterioration following a period of recovery. Some of these individuals may transition to a more linear progression of the disease, while about 15% of others begin with a progressive course on the onset of multiple sclerosis. The inflammatory response contributes to

4379-410: A standardized control framework. It is widely accepted that the synapse plays a key role in the formation of memory . The stability of long-term memory can persist for many years; nevertheless, synapses, the neurological basis of memory, are very dynamic. The formation of synaptic connections significantly depends on activity-dependent synaptic plasticity observed in various synaptic pathways. Indeed,

4530-511: A subset of patients with familial ALS. More recently, TAR DNA-binding protein 43 (TDP-43) and Fused in Sarcoma (FUS) protein aggregates have been implicated in some cases of the disease, and a mutation in chromosome 9 ( C9orf72 ) is thought to be the most common known cause of sporadic ALS. Early diagnosis of ALS is harder than with other neurodegenerative diseases as there are no highly effective means of determining its early onset. Currently, there

4681-514: A ubiquitous mediator of cellular Ca2+ signals. CaMKII is abundant in the nervous system, mainly concentrated in the synapses in the nerve cells. Indeed, CaMKII has been definitively identified as a key regulator of cognitive processes, such as learning, and neural plasticity. The first concrete experimental evidence for the long-assumed function of CaMKII in memory storage was demonstrated While Ca2+/CaM binding stimulates CaMKII activity, Ca2+-independent autonomous CaMKII activity can also be produced by

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4832-588: A variety of animal models because there is such a clearly defined trigger – repeat expansion. Extensive research has been done using the models of nematode ( C. elegans ), and fruit fly ( Drosophila ), mice, and non-human primates. Nine inherited neurodegenerative diseases are caused by the expansion of the CAG trinucleotide and polyQ tract, including Huntington's disease and the spinocerebellar ataxias . The presence of epigenetic modifications for certain genes has been demonstrated in this type of pathology. An example

4983-690: A variety of mechanisms including damage to: kinesin and cytoplasmic dynein , microtubules , cargoes, and mitochondria . When axonal transport is severely disrupted a degenerative pathway known as Wallerian-like degeneration is often triggered. Programmed cell death (PCD) is death of a cell in any form, mediated by an intracellular program. This process can be activated in neurodegenerative diseases including Parkinson's disease, amytrophic lateral sclerosis, Alzheimer's disease and Huntington's disease. PCD observed in neurodegenerative diseases may be directly pathogenic; alternatively, PCD may occur in response to other injury or disease processes. Apoptosis

5134-586: A vital role in both the induction and maintenance of LTP. For technical reasons, synaptic structure and function have been historically studied at unusually large model synapses, for example: Synapses function as ensembles within particular brain networks to control the amount of neuronal activity, which is essential for memory, learning, and behavior. Consequently, synaptic disruptions might have negative effects. In fact, alterations in cell-intrinsic molecular systems or modifications to environmental biochemical processes can lead to synaptic dysfunction. The synapse

5285-491: Is FKBP5 gene, which progressively increases its expression with age and has been related to Braak staging and increased tau pathology both in vitro and in mouse models of AD. Several neurodegenerative diseases are classified as proteopathies as they are associated with the aggregation of misfolded proteins . Protein toxicity is one of the key mechanisms of many neurodegenrative diseases. Parkinson's disease and Huntington's disease are both late-onset and associated with

5436-777: Is aging . Mitochondrial DNA mutations as well as oxidative stress both contribute to aging. Many of these diseases are late-onset, meaning there is some factor that changes as a person ages for each disease. One constant factor is that in each disease, neurons gradually lose function as the disease progresses with age. It has been proposed that DNA damage accumulation provides the underlying causative link between aging and neurodegenerative disease. About 20–40% of healthy people between 60 and 78 years old experience discernable decrements in cognitive performance in several domains including working, spatial, and episodic memory, and processing speed. A study using electronic health records indicates that 45 (with 22 of these being replicated with

5587-573: Is alpha-synuclein . In Huntington's disease, it is huntingtin . Transglutaminase substrates : Amyloid-beta , tau , alpha-synuclein and huntingtin have been proved to be substrates of transglutaminases in vitro or in vivo, that is, they can be bonded by trasglutaminases by covalent bonds to each other and potentially to any other transglutaminase substrate in the brain. Transglutaminase augmented expression: It has been proved that in these neurodegenerative diseases (Alzheimer's disease, Parkinson's disease, and Huntington's disease)

5738-471: Is a chemical or electrical synapse that forms when the axon of one neuron synapses onto dendrites of the same neuron. An influx of Na+ driven by excitatory neurotransmitters opens cation channels, depolarizing the postsynaptic membrane toward the action potential threshold. In contrast, inhibitory neurotransmitters cause the postsynaptic membrane to become less depolarized by opening either Cl- or K+ channels, reducing firing. Depending on their release location,

5889-456: Is a form of programmed cell death in multicellular organisms. It is one of the main types of programmed cell death (PCD) and involves a series of biochemical events leading to a characteristic cell morphology and death. Caspases (cysteine-aspartic acid proteases) cleave at very specific amino acid residues. There are two types of caspases: initiators and effectors . Initiator caspases cleave inactive forms of effector caspases. This activates

6040-438: Is a rare neurodegenerative disorder characterized by the gradual loss of both upper motor neurons (UMNs) and lower motor neurons (LMNs). Although initial symptoms may vary, most patients develop skeletal muscle weakness that progresses to involve the entire body. The precise etiology of ALS remains unknown. In 1993, missense mutations in the gene encoding the antioxidant enzyme superoxide dismutase 1 (SOD1) were discovered in

6191-479: Is a source of controversy among medical professionals. The gut microbiome might play a role in the diagnosis of PD, and research suggests various ways that could revolutionize the future of PD treatment. Huntington's disease (HD) is a rare autosomal dominant neurodegenerative disorder caused by mutations in the huntingtin gene (HTT) . HD is characterized by loss of medium spiny neurons and astrogliosis . The first brain region to be substantially affected

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6342-406: Is a symptom experienced by most people with ALS caused by reduced mobility. Symptoms of lower motor neuron degeneration include muscle weakness and atrophy, muscle cramps, and fleeting twitches of muscles that can be seen under the skin ( fasciculations ). Although the initial site of symptoms and subsequent rate of disability progression vary from person to person, the initially affected body region

6493-461: Is age. Mutations in genes such as α-synuclein (SNCA), leucine-rich repeat kinase 2 (LRRK2), glucocerebrosidase (GBA), and tau protein (MAPT) can also cause hereditary PD or increase PD risk. While PD is the second most common neurodegenerative disorder, problems with diagnoses still persist. Problems with the sense of smell is a widespread symptom of Parkinson's disease (PD), however, some neurologists question its efficacy. This assessment method

6644-425: Is characterized by motor impairment, epilepsy , dementia , vision loss, and shortened lifespan. A loss of vision is common first sign of Batten disease. Loss of vision is typically preceded by cognitive and behavioral changes, seizures, and loss of the ability to walk. It is common for people to establish cardiac arrhythmias and difficulties eating food as the disease progresses. Batten disease diagnosis depends on

6795-400: Is deleterious to the cell and would eventually lead to cell death. Apart from tubular structures, alpha-synuclein can also form lipoprotein nanoparticles similar to apolipoproteins. The most common form of cell death in neurodegeneration is through the intrinsic mitochondrial apoptotic pathway. This pathway controls the activation of caspase-9 by regulating the release of cytochrome c from

6946-456: Is hypothesized that defects in autophagy could be a common mechanism of neurodegeneration. PCD can also occur via non-apoptotic processes, also known as Type III or cytoplasmic cell death. For example, type III PCD might be caused by trophotoxicity, or hyperactivation of trophic factor receptors. Cytotoxins that induce PCD can cause necrosis at low concentrations, or aponecrosis (combination of apoptosis and necrosis) at higher concentrations. It

7097-569: Is more likely to be genetic in origin than adult-onset ALS; the most common genes associated with juvenile ALS are FUS , ALS2 , and SETX . Although most people with juvenile ALS live longer than those with adult-onset ALS, some of them have specific mutations in FUS and SOD1 that are associated with a poor prognosis. Late onset (after age 65) is generally associated with a more rapid functional decline and shorter survival. The disorder causes muscle weakness, atrophy , and muscle spasms throughout

7248-653: Is not known what causes sporadic ALS, hence it is described as an idiopathic disease . Though its exact cause is unknown, genetic and environmental factors are thought to be of roughly equal importance. The genetic factors are better understood than the environmental factors; no specific environmental factor has been definitively shown to cause ALS. A multi-step liability threshold model for ALS proposes that cellular damage accumulates over time due to genetic factors present at birth and exposure to environmental risks throughout life. ALS can strike at any age, but its likelihood increases with age. Most people who develop ALS are between

7399-629: Is now a licensed gene therapy ( tofersen ) specifically targeted to carriers of SOD-1 ALS. A shortage of genetic counselors and limited clinical capacity to see such at-risk individuals makes this challenging in practice, as does the unequal access to genetic testing around the world. More than 40 genes have been associated with ALS, of which four account for nearly half of familial cases, and around 5% of sporadic cases: C9orf72 (40% of familial cases, 7% sporadic), SOD1 (12% of familial cases, 1–2% sporadic), FUS (4% of familial cases, 1% sporadic), and TARDBP (4% of familial cases, 1% sporadic), with

7550-409: Is often feasible, albeit slow, and needs may change over time. Despite these challenges, many people in an advanced state of disease report satisfactory wellbeing and quality of life. Although respiratory support using non-invasive ventilation can ease problems with breathing and prolong survival, it does not affect the progression rate of ALS. Most people with ALS die between two and four years after

7701-531: Is often marked by walking with a " dropped foot " that drags gently on the ground. If the arms are affected first, they may experience difficulty with tasks requiring manual dexterity, such as buttoning a shirt, writing, or turning a key in a lock. In bulbar-onset ALS, the first symptoms are difficulty speaking or swallowing. Speech may become slurred, nasal in character, or quieter. There may be difficulty with swallowing and loss of tongue mobility. A smaller proportion of people experience "respiratory-onset" ALS, where

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7852-445: Is primarily characterized by death of dopaminergic neurons in the substantia nigra , a region of the midbrain . The cause of this selective cell death is unknown. Notably, alpha-synuclein - ubiquitin complexes and aggregates are observed to accumulate in Lewy bodies within affected neurons. It is thought that defects in protein transport machinery and regulation, such as RAB1 , may play

8003-502: Is proposed to be due to the release of antigens such as myelin oligodendrocyte glycoprotein , myelin basic protein , and proteolipid protein , causing an autoimmune response. This sets off a cascade of signaling molecules that result in T cells, B cells, and macrophages to cross the blood-brain barrier and attack myelin on neuronal axons leading to inflammation. Further release of antigens drives subsequent degeneration causing increased inflammation. Multiple sclerosis presents itself as

8154-448: Is research being done regarding the diagnosis of ALS through upper motor neuron tests. The Penn Upper Motor Neuron Score (PUMNS) consists of 28 criteria with a score range of 0–32. A higher score indicates a higher level of burden present on the upper motor neurons. The PUMNS has proven quite effective in determining the burden that exists on upper motor neurons in affected patients. Independent research provided in vitro evidence that

8305-492: Is respiratory-onset, in which the initial symptoms are difficulty breathing ( dyspnea ) upon exertion, at rest, or while lying flat ( orthopnea ). Primary lateral sclerosis (PLS) is a subtype of the overall ALS category which accounts for about 5% of all cases and only affects the upper motor neurons in the arms, legs, and bulbar region. However, more than 75% of people with apparent PLS go on to later develop lower motor neuron signs within four years of symptom onset, meaning that

8456-401: Is still unclear exactly what combination of apoptosis, non-apoptosis, and necrosis causes different kinds of aponecrosis. Transglutaminases are human enzymes ubiquitously present in the human body and in the brain in particular. The main function of transglutaminases is bind proteins and peptides intra- and intermolecularly, by a type of covalent bonds termed isopeptide bonds , in

8607-620: Is strengthened as the action of the transmitter is prolonged. For example, Prozac is an antidepressant medication that works by preventing the absorption of serotonin neurotransmitter. Also, other antidepressants operate by inhibiting the reabsorption of both serotonin and norepinephrine. In nerve terminals, synaptic vesicles are produced quickly to compensate for their rapid depletion during neurotransmitter release. Their biogenesis involves segregating synaptic vesicle membrane proteins from other cellular proteins and packaging those distinct proteins into vesicles of appropriate size. Besides, it entails

8758-400: Is subpar, and better methods need to be utilized for various aspects of clinical diagnoses. Alzheimer's has a 20% misdiagnosis rate. AD pathology is primarily characterized by the presence of amyloid plaques and neurofibrillary tangles . Plaques are made up of small peptides , typically 39–43 amino acids in length, called amyloid beta (also written as A-beta or Aβ). Amyloid beta is

8909-449: Is the striatum , followed by degeneration of the frontal and temporal cortices. The striatum's subthalamic nuclei send control signals to the globus pallidus , which initiates and modulates motion. The weaker signals from subthalamic nuclei thus cause reduced initiation and modulation of movement, resulting in the characteristic movements of the disorder, notably chorea . Huntington's disease presents itself later in life even though

9060-400: Is the common name for a group of lysosomal storage disorders known as neuronal ceroid lipofuscinoses (NCLs) – each caused by a specific gene mutation, of which there are thirteen. Since Batten disease is quite rare, its worldwide prevalence is about 1 in every 100,000 live births. In North America, NCL3 disease (juvenile NCL) typically manifests between the ages of 4 and 7. Batten disease

9211-445: Is the main transporter that removes glutamate from the synapse; this leads to increased synaptic glutamate levels and excitotoxicity. Riluzole , a drug that modestly prolongs survival in ALS, inhibits glutamate release from pre-synaptic neurons; however, it is unclear if this mechanism is responsible for its therapeutic effect. No single test can provide a definite diagnosis of ALS. Instead,

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9362-466: Is the most common neurodegenerative disease. Even with billions of dollars being used to find a treatment for Alzheimer's disease, no effective treatments have been found. Within clinical trials stable and effective AD therapeutic strategies have a 99.5% failure rate. Reasons for this failure rate include inappropriate drug doses, invalid target and participant selection, and inadequate knowledge of pathophysiology of AD. Currently, diagnoses of Alzheimer's

9513-534: Is the primary unit of information transfer in the nervous system, and correct synaptic contact creation during development is essential for normal brain function. In addition, several mutations have been connected to neurodevelopmental disorders, and that compromised function at different synapse locations is a hallmark of neurodegenerative diseases. Synaptic defects are causally associated with early appearing neurological diseases, including autism spectrum disorders (ASD), schizophrenia (SCZ), and bipolar disorder (BP). On

9664-420: Is thought that misfolded mutant SOD1 can cause misfolding and aggregation of wild-type SOD1 in neighboring neurons in a prion-like manner. Other protein degradation genes that can cause ALS when mutated include VCP , OPTN , TBK1 , and SQSTM1 . Three genes implicated in ALS that are important for maintaining the cytoskeleton and for axonal transport include DCTN1 , PFN1 , and TUBA4A . There are

9815-401: Is thought that mutations in TARDBP and FUS increase the binding affinity of the low-complexity domain, causing their respective proteins to aggregate in the cytoplasm. Once these mutant RNA-binding proteins are misfolded and aggregated, they may be able to misfold normal proteins both within and between cells in a prion-like manner. This also leads to decreased levels of RNA-binding protein in

9966-427: Is thought to account for 10–15% of cases overall and can include monogenic , oligogenic , and polygenic modes of inheritance. There is considerable variation among clinicians on how to approach genetic testing in ALS, and only about half discuss the possibility of genetic inheritance with their patients, particularly if there is no discernible family history of the disease. In the past, genetic counseling and testing

10117-435: Is thought to result in the storage of information, resulting in memory. This process of synaptic strengthening is known as long-term potentiation (LTP) . By altering the release of neurotransmitters, the plasticity of synapses can be controlled in the presynaptic cell. The postsynaptic cell can be regulated by altering the function and number of its receptors. Changes in postsynaptic signaling are most commonly associated with

10268-430: Is usually the most affected over time, and symptoms usually spread to a neighbouring body region. For example, symptoms starting in one arm usually spread next to either the opposite arm or to the leg on the same side. Bulbar-onset patients most typically get their next symptoms in their arms rather than legs, arm-onset patients typically spreads to the legs before the bulbar region, and leg-onset patients typically spread to

10419-472: The ALS Functional Rating Scale - Revised (ALSFRS-R), a 12-item instrument survey administered as a clinical interview or self-reported questionnaire that produces a score between 48 (normal function) and 0 (severe disability). The ALSFRS-R is the most frequently used outcome measure in clinical trials and is used by doctors to track disease progression. Though the degree of variability is high and

10570-500: The UK Biobank ) viral exposures can significantly elevate risks of neurodegenerative disease, including up to 15 years after infection. Many neurodegenerative diseases are caused by genetic mutations , most of which are located in completely unrelated genes. In many of the different diseases, the mutated gene has a common feature: a repeat of the CAG nucleotide triplet. CAG codes for the amino acid glutamine . A repeat of CAG results in

10721-454: The expression of the transglutaminase enzyme is increased. Presence of isopeptide bonds in these structures: The presence of isopeptide bonds (the result of the transglutaminase reaction) have been detected in the abnormal structures that are characteristic of these neurodegenerative diseases . Co-localization: Co-localization of transglutaminase mediated isopeptide bonds with these abnormal structures has been detected in

10872-424: The intercostal muscles that support breathing are affected first. Over time, people experience increasing difficulty moving, swallowing ( dysphagia ), and speaking or forming words ( dysarthria ). Symptoms of upper motor neuron involvement include tight and stiff muscles ( spasticity ) and exaggerated reflexes ( hyperreflexia ), including an overactive gag reflex. While the disease does not cause pain directly, pain

11023-465: The lower motor neurons in the spinal cord. Primary lateral sclerosis (PLS) involves degeneration of only the upper motor neurons, and progressive muscular atrophy (PMA) involves only the lower motor neurons. There is debate over whether PLS and PMA are separate diseases or simply variants of ALS. Classical ALS accounts for about 70% of all cases of ALS and can be subdivided into where symptoms first appear as these are usually focussed to one region of

11174-573: The mitochondrial intermembrane space . Reactive oxygen species (ROS) are normal byproducts of mitochondrial respiratory chain activity. ROS concentration is mediated by mitochondrial antioxidants such as manganese superoxide dismutase (SOD2) and glutathione peroxidase . Over production of ROS ( oxidative stress ) is a central feature of all neurodegenerative disorders. In addition to the generation of ROS, mitochondria are also involved with life-sustaining functions including calcium homeostasis, PCD, mitochondrial fission and fusion , lipid concentration of

11325-430: The neuromuscular junction , such as myasthenia gravis (MG) and Lambert–Eaton myasthenic syndrome , may also mimic ALS, although this rarely presents diagnostic difficulty over time. Benign fasciculation syndrome and cramp fasciculation syndrome may also, occasionally, mimic some of the early symptoms of ALS. Nonetheless, the absence of other neurological features that develop inexorably with ALS means that, over time,

11476-541: The pathogenesis of ALS. It is still not fully understood why neurons die in ALS, but this neurodegeneration is thought to involve many different cellular and molecular processes. The genes known to be involved in ALS can be grouped into three general categories based on their normal function: protein degradation, the cytoskeleton , and RNA processing. Mutant SOD1 protein forms intracellular aggregations that inhibit protein degradation. Cytoplasmic aggregations of wild-type (normal) SOD1 protein are common in sporadic ALS. It

11627-859: The (GPCR) CB1 receptor located at the presynaptic terminal, are involved in this modulation by a retrograde signaling process, in which these compounds are synthesized in and released from postsynaptic neuronal elements and travel back to the presynaptic terminal to act on the CB1 receptor for short-term or long-term synaptic depression, that causes a short or long lasting decrease in neurotransmitter release. Drugs have long been considered crucial targets for transmitter-gated ion channels. The majority of medications utilized to treat schizophrenia, anxiety, depression, and sleeplessness work at chemical synapses, and many of these pharmaceuticals function by binding to transmitter-gated channels. For instance, some drugs like barbiturates and tranquilizers bind to GABA receptors and enhance

11778-659: The abilities to eat, speak, move, and, lastly, breathe are all lost. While only 15% of people with ALS also fully develop frontotemporal dementia , an estimated 50% face at least some minor difficulties with thinking and behavior . Depending on which of the aforementioned symptoms develops first, ALS is classified as limb-onset (begins with weakness in the arms or legs) or bulbar-onset (begins with difficulty in speaking or swallowing ). Most cases of ALS (about 90–95%) have no known cause , and are known as sporadic ALS . However, both genetic and environmental factors are believed to be involved. The remaining 5–10% of cases have

11929-416: The ability to initiate and control all voluntary movement, known as locked-in syndrome . Bladder and bowel function are usually spared, meaning urinary and fecal incontinence are uncommon, although trouble getting to a toilet can lead to difficulties. The extraocular muscles responsible for eye movement are usually spared, meaning the use of eye tracking technology to support augmentative communication

12080-419: The above personality traits might underlie lifestyle choices which are in turn risk factors for ALS. Upon examination at autopsy, features of the disease that can be seen with the naked eye include skeletal muscle atrophy , motor cortex atrophy, sclerosis of the corticospinal and corticobulbar tracts , thinning of the hypoglossal nerves (which control the tongue), and thinning of the anterior roots of

12231-723: The accumulation of intracellular toxic proteins. Diseases caused by the aggregation of proteins are known as proteopathies , and they are primarily caused by aggregates in the following structures: There are two main avenues eukaryotic cells use to remove troublesome proteins or organelles: Damage to the membranes of organelles by monomeric or oligomeric proteins could also contribute to these diseases. Alpha-synuclein can damage membranes by inducing membrane curvature, and cause extensive tubulation and vesiculation when incubated with artificial phospholipid vesicles. The tubes formed from these lipid vesicles consist of both micellar as well as bilayer tubes. Extensive induction of membrane curvature

12382-463: The age of 60. The average survival from onset to death is two to four years, though this can vary, and about 10% of those affected survive longer than ten years. Descriptions of the disease date back to at least 1824 by Charles Bell . In 1869, the connection between the symptoms and the underlying neurological problems was first described by French neurologist Jean-Martin Charcot , who in 1874 began using

12533-422: The age of onset. While the peak age of onset is 58 to 63 for sporadic ALS and 47 to 52 for genetic ALS, about 10% of all cases of ALS begin before age 45 ("young-onset" ALS), and about 1% of all cases begin before age 25 ("juvenile" ALS). People who develop young-onset ALS are more likely to be male, less likely to have bulbar onset of symptoms, and more likely to have a slower progression of the disease. Juvenile ALS

12684-507: The ages of 40 and 70, with an average age of 55 at the time of diagnosis. ALS is 20% more common in men than women, but this difference in sex distribution is no longer present in patients with onset after age 70. While they appear identical clinically and pathologically, ALS can be classified as being either familial or sporadic, depending on whether there is a known family history of the disease and/or whether an ALS-associated genetic mutation has been identified via genetic testing. Familial ALS

12835-480: The arms rather than the bulbar region. Over time, regardless of where symptoms began, most people eventually lose the ability to walk or use their hands and arms independently. Less consistently, they may lose the ability to speak and to swallow food. It is the eventual development of weakness of the respiratory muscles, with the loss of ability to cough and to breathe without support, that is ultimately life-shortening in ALS. The rate of progression can be measured using

12986-494: The arms, legs, and bulbar region. While PMA is associated with longer survival on average than classical ALS, it is still progressive over time, eventually leading to respiratory failure and death. As with PLS developing into classical ALS, PMA can also develop into classical ALS over time if the lower motor neuron involvement progresses to include upper motor neurons, in which case the diagnosis might be changed to classic ALS. Isolated variants of ALS have symptoms that are limited to

13137-502: The autopsy of brains of patients with these diseases. The process of neurodegeneration is not well understood, so the diseases that stem from it have, as yet, no cures. In the search for effective treatments (as opposed to palliative care ), investigators employ animal models of disease to test potential therapeutic agents. Model organisms provide an inexpensive and relatively quick means to perform two main functions: target identification and target validation. Together, these help show

13288-448: The axon can synapse onto a dendrite, onto a cell body, or onto another axon or axon terminal, as well as into the bloodstream or diffusely into the adjacent nervous tissue. Neurotransmitters are tiny signal molecules stored in membrane-enclosed synaptic vesicles and released via exocytosis. Indeed, a change in electrical potential in the presynaptic cell triggers the release of these molecules. By attaching to transmitter-gated ion channels,

13439-513: The axon), and for these signals to then be received and carried on by post-synaptic neurons or received by effector cells. Nerve cells have long been used as models for cellular polarization, and of particular interest are the mechanisms underlying the polarized localization of synaptic molecules. PIP2 signaling regulated by IMPase plays an integral role in synaptic polarity. Phosphoinositides ( PIP , PIP2, and PIP3 ) are molecules that have been shown to affect neuronal polarity. A gene ( ttx-7 )

13590-460: The body at initial presentation before later spread. Limb-onset ALS (also known as spinal-onset) and bulbar-onset ALS. Limb-onset ALS begins with weakness in the hands, arms, feet, and/or legs and accounts for about two-thirds of all classical ALS cases. Bulbar-onset ALS begins with weakness in the muscles of speech, chewing, and swallowing and accounts for about 25% of classical ALS cases. A rarer type of classical ALS affecting around 3% of patients

13741-417: The body due to the degeneration of the upper motor and lower motor neurons. Sensory nerves and the autonomic nervous system are generally unaffected, meaning the majority of people with ALS maintain hearing , sight , touch , smell , and taste . The start of ALS may be so subtle that the symptoms are overlooked. The earliest symptoms of ALS are muscle weakness or muscle atrophy, typically on one side of

13892-498: The body. Other presenting symptoms include trouble swallowing or breathing, cramping, or stiffness of affected muscles; muscle weakness affecting an arm or a leg; or slurred and nasal speech. The parts of the body affected by early symptoms of ALS depend on which motor neurons in the body are damaged first. In limb-onset ALS, the first symptoms are in the arms or the legs. If the legs are affected first, people may experience awkwardness, tripping, or stumbling when walking or running; this

14043-399: The brain to muscle, causes different types of symptoms. Damage to the upper motor neuron typically causes spasticity including stiffness and increased tendon reflexes , and/or clonus , while damage to the lower motor neuron typically causes weakness , muscle atrophy , and fasciculations . Classical, or classic ALS, involves degeneration to both the upper motor neurons in the brain and

14194-429: The case of electrical synapses , neurons are coupled bidirectionally with each other through gap junctions and have a connected cytoplasmic milieu. These types of synapses are known to produce synchronous network activity in the brain, but can also result in complicated, chaotic network level dynamics. Therefore, signal directionality cannot always be defined across electrical synapses. Synapses are essential for

14345-427: The cell, even when its concentration is much higher outside than inside. The reversal potential for Cl- in many neurons is quite negative, nearly equal to the resting potential . Opening Cl- channels tends to buffer the membrane potential, but this effect is countered when the membrane starts to depolarize, allowing more negatively charged Cl- ions to enter the cell. Consequently, it becomes more difficult to depolarize

14496-479: The cleft between the two. Chemical and electrical synapses are two ways of synaptic transmission. The formation of neural circuits in nervous systems appears to heavily depend on the crucial interactions between chemical and electrical synapses. Thus these interactions govern the generation of synaptic transmission. Synaptic communication is distinct from an ephaptic coupling , in which communication between neurons occurs via indirect electric fields. An autapse

14647-462: The condition, but as of 2023 are not in general medical use. Because symptoms of ALS can be similar to those of a wide variety of other, more treatable diseases or disorders, appropriate tests must be conducted to exclude the possibility of other conditions. One of these tests is electromyography (EMG), a special recording technique that detects electrical activity in muscles. Certain EMG findings can support

14798-411: The connection between memory formation and alterations in synaptic efficacy enables the reinforcement of neuronal interactions between neurons. As neurotransmitters activate receptors across the synaptic cleft, the connection between the two neurons is strengthened when both neurons are active at the same time, as a result of the receptor's signaling mechanisms. The strength of two connected neural pathways

14949-442: The cytoplasm of motor neurons. In about 97% of people with ALS, the main component of the inclusion bodies is TDP-43 protein; however, in those with SOD1 or FUS mutations, the main component of the inclusion bodies is SOD1 protein or FUS protein, respectively. Prion -like propagation of misfolded proteins from cell to cell may explain why ALS starts in one area and spreads to others. The glymphatic system may also be involved in

15100-492: The dense extracellular amyloid plaques. Parkinson's disease (PD) is the second most common neurodegenerative disorder. It typically manifests as bradykinesia , rigidity, resting tremor and posture instability. The crude prevalence rate of PD has been reported to range from 15 per 100,000 to 12,500 per 100,000, and the incidence of PD from 15 per 100,000 to 328 per 100,000, with the disease being less common in Asian countries. PD

15251-422: The diagnosis of ALS is primarily made based on a physician's clinical assessment after ruling out other diseases. Physicians often obtain the person's full medical history and conduct neurologic examinations at regular intervals to assess whether signs and symptoms such as muscle weakness, muscle atrophy , hyperreflexia , Babinski's sign , and spasticity are worsening. A number of biomarkers are being studied for

15402-483: The diagnosis of ALS. Another common test measures nerve conduction velocity (NCV). Specific abnormalities in the NCV results may suggest, for example, that the person has a form of peripheral neuropathy (damage to peripheral nerves) or myopathy (muscle disease) rather than ALS. While a magnetic resonance imaging (MRI) is often normal in people with early-stage ALS, it can reveal evidence of other problems that may be causing

15553-420: The diagnosis. Around 50% of people with ALS die within 30 months of their symptoms beginning, about 20% live between five and ten years, and about 10% survive for 10 years or longer. The most common cause of death among people with ALS is respiratory failure , often accelerated by pneumonia . Most ALS patients die at home after a period of worsening difficulty breathing, a decline in their nutritional status, or

15704-424: The disease and should be considered. ALS must be differentiated from the "ALS mimic syndromes", which are unrelated disorders that may have a similar presentation and clinical features to ALS or its variants. Because the prognosis of ALS and closely related subtypes of motor neuron disease are generally poor, neurologists may carry out investigations to evaluate and exclude other diagnostic possibilities. Disorders of

15855-481: The disease progression, and improve symptoms. FDA approved treatments that slow the progression of ALS include riluzole and edaravone . Non-invasive ventilation may result in both improved quality, and length of life. Mechanical ventilation can prolong survival but does not stop disease progression. A feeding tube may help maintain weight and nutrition. Death is usually caused by respiratory failure. The disease can affect people of any age, but usually starts around

16006-489: The disease. Multiple sclerosis (MS) is a chronic debilitating demyelinating disease of the central nervous system , caused by an autoimmune attack resulting in the progressive loss of myelin sheath on neuronal axons. The resultant decrease in the speed of signal transduction leads to a loss of functionality that includes both cognitive and motor impairment depending on the location of the lesion. The progression of MS occurs due to episodes of increasing inflammation, which

16157-402: The distinction will not present any difficulty to the experienced neurologist; where doubt remains, EMG may be helpful. Neurodegenerative disease Within neurodegenerative diseases, it is estimated that 55 million people worldwide had dementia in 2019, and that by 2050 this figure will increase to 139 million people. The consequences of neurodegeneration can vary widely depending on

16308-428: The effectiveness of synaptic transmission. In fact, the concentration of cytoplasmic calcium is involved in regulating the release of neurotransmitters from presynaptic neurons. The chemical transmission involves several sequential processes: The function of neurons depends upon cell polarity . The distinctive structure of nerve cells allows action potentials to travel directionally (from dendrites to cell body down

16459-410: The effectors that in turn cleave other proteins resulting in apoptotic initiation. Autophagy is a form of intracellular phagocytosis in which a cell actively consumes damaged organelles or misfolded proteins by encapsulating them into an autophagosome , which fuses with a lysosome to destroy the contents of the autophagosome. Because many neurodegenerative diseases show unusual protein aggregates, it

16610-557: The endocytosis of synaptic vesicle membrane proteins from the plasma membrane. Synaptoblastic and synaptoclastic refer to synapse-producing and synapse-removing activities within the biochemical signalling chain. This terminology is associated with the Bredesen Protocol for treating Alzheimer's disease , which conceptualizes Alzheimer's as an imbalance between these processes. As of October 2023, studies concerning this protocol remain small and few results have been obtained within

16761-462: The excitatory neurotransmitter glutamate , is a mechanism thought to be common to all forms of ALS. Motor neurons are more sensitive to excitotoxicity than other types of neurons because they have a lower calcium-buffering capacity and a type of glutamate receptor (the AMPA receptor ) that is more permeable to calcium. In ALS, there are decreased levels of excitatory amino acid transporter 2 ( EAAT2 ), which

16912-434: The formation of synapses, with various types working together to achieve the remarkable specificity of synapses. In essence, SAMs function in both excitatory and inhibitory synapses , likely serving as the mediator for signal transmission. Santiago Ramón y Cajal proposed that neurons are not continuous throughout the body, yet still communicate with each other, an idea known as the neuron doctrine . The word "synapse"

17063-562: The gradual build-up of protein aggregates in neurons, the composition of which may vary based on the pathology; all have the same deleterious effects on neuronal integrity. Furthermore, the high number of mutations linked to synaptic structure and function, as well as dendritic spine alterations in post-mortem tissue, has led to the association between synaptic defects and neurodevelopmental disorders, such as ASD and SCZ, characterized by abnormal behavioral or cognitive phenotypes. Nevertheless, due to limited access to human tissue at late stages and

17214-410: The inhibitory effect of GABA neurotransmitter. Thus, reduced concentration of GABA enables the opening of Cl- channels. Furthermore, psychoactive drugs could potentially target many other synaptic signalling machinery components. In fact, numerous neurotransmitters are released by Na+-driven carriers and are subsequently removed from the synaptic cleft. By inhibiting such carriers, synaptic transmission

17365-871: The likelihood of a very rare condition by a small amount. For instance an individual's lifetime risk of developing ALS might go from "1 in 400" without an exposure to between "1 in 300" and "1 in 200" if they were exposed to heavy metals. A range of other exposures have weaker evidence supporting them and include participation in professional sports , having a lower body mass index , lower educational attainment , manual occupations, military service, exposure to Beta-N-methylamino-L-alanin (BMAA), and viral infections. Although some personality traits, such as openness , agreeableness and conscientiousness appear remarkably common among patients with ALS, it remains open whether personality can increase susceptibility to ALS directly. Instead, genetic factors giving rise to personality might simultaneously predispose people to developing ALS, or

17516-519: The loss of the grey matter, and as a result current literature devotes itself to combatting the auto-inflammatory aspect of the disease. While there are several proposed causal links between EBV and the HLA-DRB1*15:01 allele to the onset of MS – they may contribute to the degree of autoimmune attack and the resultant inflammation – they do not determine the onset of MS. Amyotrophic lateral sclerosis (ALS), commonly referred to Lou Gehrig's disease,

17667-402: The membrane and excite the cell when Cl- channels are open. Similar effects result from the opening of K+ channels. The significance of inhibitory neurotransmitters is evident from the effects of toxins that impede their activity. For instance, strychnine binds to glycine receptors, blocking the action of glycine and leading to muscle spasms, convulsions, and death. Synapses can be classified by

17818-405: The membrane of the target ( postsynaptic ) cell. Both the presynaptic and postsynaptic sites contain extensive arrays of molecular machinery that link the two membranes together and carry out the signaling process. In many synapses, the presynaptic part is located on the terminals of axons and the postsynaptic part is located on a dendrite or soma . Astrocytes also exchange information with

17969-714: The mitochondrial membranes, and the mitochondrial permeability transition. Mitochondrial disease leading to neurodegeneration is likely, at least on some level, to involve all of these functions. There is strong evidence that mitochondrial dysfunction and oxidative stress play a causal role in neurodegenerative disease pathogenesis, including in four of the more well known diseases Alzheimer's , Parkinson's , Huntington's , and amyotrophic lateral sclerosis . Neurons are particularly vulnerable to oxidative damage due to their strong metabolic activity associated with high transcription levels, high oxygen consumption, and weak antioxidant defense. The brain metabolizes as much as

18120-412: The neuronal death that is responsible for the symptoms of Alzheimer's disease. Synapse In the nervous system , a synapse is a structure that allows a neuron (or nerve cell) to pass an electrical or chemical signal to another neuron or a target effector cell. Synapses can be classified as either chemical or electrical, depending on the mechanism of signal transmission between neurons. In

18271-404: The neurotransmitter causes an electrical alteration in the postsynaptic cell and rapidly diffuses across the synaptic cleft. Once released, the neurotransmitter is swiftly eliminated, either by being absorbed by the nerve terminal that produced it, taken up by nearby glial cells, or broken down by specific enzymes in the synaptic cleft. Numerous Na+-dependent neurotransmitter carrier proteins recycle

18422-408: The neurotransmitters and enable the cells to maintain rapid rates of release. At chemical synapses, transmitter-gated ion channels play a vital role in rapidly converting extracellular chemical impulses into electrical signals. These channels are located in the postsynaptic cell's plasma membrane at the synapse region, and they temporarily open in response to neurotransmitter molecule binding, causing

18573-725: The nucleus, translation of the RNA into toxic dipeptide repeat proteins in the cytoplasm, and decreased levels of the normal C9orf72 protein. Mitochondrial bioenergetic dysfunction leading to dysfunctional motor neuron axonal homeostasis (reduced axonal length and fast axonal transport of mitochondrial cargo) has been shown to occur in C9orf72 -ALS using human induced pluripotent stem cell (iPSC) technologies coupled with CRISPR/Cas9 gene-editing, and human post-mortem spinal cord tissue examination. Excitotoxicity , or nerve cell death caused by high levels of intracellular calcium due to excessive stimulation by

18724-701: The nucleus, which may mean that their target RNA transcripts do not undergo normal processing. Other RNA metabolism genes associated with ALS include ANG , SETX , and MATR3 . C9orf72 is the most commonly mutated gene in ALS and causes motor neuron death through a number of mechanisms. The pathogenic mutation is a hexanucleotide repeat expansion (a series of six nucleotides repeated over and over); people with up to 30 repeats are considered normal, while people with hundreds or thousands of repeats can have familial ALS, frontotemporal dementia, or sometimes sporadic ALS. The three mechanisms of disease associated with these C9orf72 repeats are deposition of RNA transcripts in

18875-407: The other hand, in late-onset degenerative pathologies, such as Alzheimer's (AD), Parkinson's (PD), and Huntington's (HD) diseases, synaptopathy is thought to be the inevitable end-result of an ongoing pathophysiological cascade. These diseases are identified by a gradual loss in cognitive and behavioral function and a steady loss of brain tissue. Moreover, these deteriorations have been mostly linked to

19026-453: The patient struggle to react appropriately to what can be frequent and inappropriate outbursts in public. In addition to mild changes in cognition that may only emerge during neuropsychological testing, around 10–15% of individuals have signs of frontotemporal dementia (FTD). Repeating phrases or gestures , apathy, and loss of inhibition are the most frequently reported behavioral features of ALS. ALS and FTD are now considered to be part of

19177-705: The pivotal CONNECTION trial of patients with mild-to-moderate disease. With CONCERT, the remaining Pfizer and Medivation Phase III trial for Dimebon (latrepirdine) in Alzheimer's disease failed in 2012, effectively ending the development in this indication. In another experiment using a rat model of Alzheimer's disease, it was demonstrated that systemic administration of hypothalamic proline-rich peptide (PRP)-1 offers neuroprotective effects and can prevent neurodegeneration in hippocampus amyloid-beta 25–35. This suggests that there could be therapeutic value to PRP-1. Protein degradation offers therapeutic options both in preventing

19328-483: The presynaptic terminal, can decrease the probability of neurotransmitter release. This presynaptic depression involves activation of Gi/o -type G-proteins that mediate different inhibitory mechanisms, including inhibition of voltage-gated calcium channels , activation of potassium channels , and direct inhibition of the vesicle fusion process. Endocannabinoids , synthesized in and released from postsynaptic neuronal elements and their cognate receptors , including

19479-441: The primary cellular sites where SOD1 mutations act are located on astrocytes . Astrocytes then cause the toxic effects on the motor neurons . The specific mechanism of toxicity still needs to be investigated, but the findings are significant because they implicate cells other than neuron cells in neurodegeneration. Batten disease is a rare and fatal recessive neurodegenerative disorder that begins in childhood. Batten disease

19630-686: The proteins that cause the disease works towards manifestation from their early stages in the humans affected by the proteins. Along with being a neurodegenerative disorder, HD has links to problems with neurodevelopment. HD is caused by polyglutamine tract expansion in the huntingtin gene, resulting in the mutant huntingtin. Aggregates of mutant huntingtin form as inclusion bodies in neurons, and may be directly toxic. Additionally, they may damage molecular motors and microtubules to interfere with normal axonal transport , leading to impaired transport of important cargoes such as BDNF . Huntington's disease currently has no effective treatments that would modify

19781-586: The receptors they bind to, and the ionic circumstances they encounter, various transmitters can be either excitatory or inhibitory. For instance, acetylcholine can either excite or inhibit depending on the type of receptors it binds to. For example, glutamate serves as an excitatory neurotransmitter, in contrast to GABA, which acts as an inhibitory neurotransmitter. Additionally, dopamine is a neurotransmitter that exerts dual effects, displaying both excitatory and inhibitory impacts through binding to distinct receptors. The membrane potential prevents Cl- from entering

19932-903: The remaining genes mostly accounting for fewer than 1% of either familial or sporadic cases. ALS genes identified to date explain the cause of about 70% of familial ALS and about 15% of sporadic ALS. Overall, first-degree relatives of an individual with ALS have a ~1% risk of developing ALS themselves. The multi-step hypothesis suggests the disease is caused by some interaction between an individual's genetic risk factors and their cumulative lifetime of exposures to environmental factors, termed their exposome . The most consistent lifetime exposures associated with developing ALS (other than genetic mutations) include heavy metals (e.g. lead and mercury ), chemicals (e.g. pesticides and solvents ), electric shock , physical injury (including head injury ), and smoking (in men more than women). Overall these effects are small, with each exposure in isolation only increasing

20083-507: The research process for methods to treat Batten disease. Creutzfeldt–Jakob disease (CJD) is a prion disease that is characterized by rapidly progressive dementia. Misfolded proteins called prions aggregate in brain tissue leading to nerve cell death. Variant Creutzfeldt–Jakob disease (vCJD) is the infectious form that comes from the meat of a cow that was infected with bovine spongiform encephalopathy , also called mad cow disease. The greatest risk factor for neurodegenerative diseases

20234-416: The specific region affected, ranging from issues related to movement to the development of dementia. Alzheimer's disease (AD) is a chronic neurodegenerative disease that results in the loss of neurons and synapses in the cerebral cortex and certain subcortical structures, resulting in gross atrophy of the temporal lobe , parietal lobe , and parts of the frontal cortex and cingulate gyrus . It

20385-445: The spinal cord. The defining feature of ALS is the death of both upper motor neurons (located in the motor cortex of the brain) and lower motor neurons (located in the brainstem and spinal cord). In ALS with frontotemporal dementia, neurons throughout the frontal and temporal lobes of the brain die as well. The pathological hallmark of ALS is the presence of inclusion bodies (abnormal aggregations of protein) known as Bunina bodies in

20536-404: The symptoms, such as a spinal cord tumor, multiple sclerosis , a herniated disc in the neck, syringomyelia , or cervical spondylosis . Based on the person's symptoms and findings from the examination and from these tests, the physician may order tests on blood and urine samples to eliminate the possibility of other diseases, as well as routine laboratory tests. In some cases, for example, if

20687-411: The synapse. Recently, mechanical tension, a phenomenon never thought relevant to synapse function has been found to be required for those on hippocampal neurons to fire. Neurotransmitters bind to ionotropic receptors on postsynaptic neurons, either causing their opening or closing. The variations in the quantities of neurotransmitters released from the presynaptic neuron may play a role in regulating

20838-486: The synaptic gap remained a theoretical construct, and was sometimes reported as a discontinuity between contiguous axonal terminations and dendrites or cell bodies, histological methods using the best light microscopes of the day could not visually resolve their separation which is now known to be about 20 nm. It needed the electron microscope in the 1950s to show the finer structure of the synapse with its separate, parallel pre- and postsynaptic membranes and processes, and

20989-400: The synaptic neurons, responding to synaptic activity and, in turn, regulating neurotransmission . Synapses (at least chemical synapses) are stabilized in position by synaptic adhesion molecules (SAMs) [1] projecting from both the pre- and post-synaptic neuron and sticking together where they overlap; SAMs may also assist in the generation and functioning of synapses. Moreover, SAMs coordinate

21140-550: The synthesis and degradation of irregular proteins. There is also interest in upregulating autophagy to help clear protein aggregates implicated in neurodegeneration. Both of these options involve very complex pathways that we are only beginning to understand. The goal of immunotherapy is to enhance aspects of the immune system. Both active and passive vaccinations have been proposed for Alzheimer's disease and other conditions; however, more research must be done to prove safety and efficacy in humans. A current therapeutic target for

21291-416: The term amyotrophic lateral sclerosis . ALS is a motor neuron disease , which is a group of neurological disorders that selectively affect motor neurons , the cells that control voluntary muscles of the body. Other motor neuron diseases include primary lateral sclerosis (PLS), progressive muscular atrophy (PMA), progressive bulbar palsy , pseudobulbar palsy , and monomelic amyotrophy (MMA). As

21442-451: The transmission of neuronal impulses from one neuron to the next, playing a key role in enabling rapid and direct communication by creating circuits. In addition, a synapse serves as a junction where both the transmission and processing of information occur, making it a vital means of communication between neurons. At the synapse, the plasma membrane of the signal-passing neuron (the presynaptic neuron) comes into close apposition with

21593-416: The treatment of Alzheimer's disease is the protease β-secretase , which is involved in the amyloidogenic processing pathway that leads to the pathological accumulation of proteins in the brain. When the gene that encodes for amyloid precursor protein (APP) is spliced by α-secretase rather than β-secretase, the toxic protein β amyloid is not produced. Targeted inhibition of β-secretase can potentially prevent

21744-438: The type of cellular structures serving as the pre- and post-synaptic components. The vast majority of synapses in the mammalian nervous system are classical axo-dendritic synapses (axon synapsing upon a dendrite), however, a variety of other arrangements exist. These include but are not limited to axo-axonic , dendro-dendritic , axo-secretory, axo-ciliary, somato-dendritic, dendro-somatic, and somato-somatic synapses. In fact,

21895-403: The types of motor neurons that are affected. To successfully control any voluntary muscle in the body, a signal must be sent from the motor cortex in the brain down the upper motor neuron as it travels down the spinal cord. There, it connects via a synapse to the lower motor neuron which connects to the muscle itself. Damage to either the upper or lower motor neuron, as it makes its way from

22046-506: The upper arms symmetrically and progressing downwards to the hands. Flail leg syndrome is characterized by lower motor neuron damage leading to asymmetrical weakness and wasting in the legs starting around the feet. Isolated bulbar palsy is characterized by upper or lower motor neuron damage in the bulbar region (in the absence of limb symptoms for at least 20 months), leading to gradual onset of difficulty with speech ( dysarthria ) and swallowing ( dysphagia ). ALS can also be classified based on

22197-498: The value of any specific therapeutic strategies and drugs when attempting to ameliorate disease severity. An example is the drug Dimebon by Medivation, Inc. In 2009 this drug was in phase III clinical trials for use in Alzheimer's disease, and also phase II clinical trials for use in Huntington's disease. In March 2010, the results of a clinical trial phase III were released; the investigational Alzheimer's disease drug Dimebon failed in

22348-502: Was an unusual case. Cognitive impairment or behavioral dysfunction is present in 30–50% of individuals with ALS, and can appear more frequently in later stages of the disease. Language dysfunction , executive dysfunction , and troubles with social cognition and verbal memory are the most commonly reported cognitive symptoms in ALS. Cognitive impairment is found more frequently in patients with C9orf72 gene repeat expansions, bulbar onset, bulbar symptoms, family history of ALS, and/or

22499-502: Was identified in Caenorhabditis elegans that encodes myo -inositol monophosphatase (IMPase), an enzyme that produces inositol by dephosphorylating inositol phosphate . Organisms with mutant ttx-7 genes demonstrated behavioral and localization defects, which were rescued by expression of IMPase. This led to the conclusion that IMPase is required for the correct localization of synaptic protein components. The egl-8 gene encodes

22650-734: Was introduced in 1897 by the English neurophysiologist Charles Sherrington in Michael Foster 's Textbook of Physiology . Sherrington struggled to find a good term that emphasized a union between two separate elements, and the actual term "synapse" was suggested by the English classical scholar Arthur Woollgar Verrall , a friend of Foster. The word was derived from the Greek synapsis ( σύναψις ), meaning "conjunction", which in turn derives from synaptein ( συνάπτειν ), from syn ( σύν ) "together" and haptein ( ἅπτειν ) "to fasten". However, while

22801-494: Was only offered to those with obviously familial ALS. But it is increasingly recognized that cases of sporadic ALS may also be due to disease-causing de novo mutations in SOD1 , or C9orf72 , an incomplete family history, or incomplete penetrance , meaning that a patient's ancestors carried the gene but did not express the disease in their lifetimes. The lack of positive family history may be caused by lack of historical records, having

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