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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| ALS | 6/11 | https://en.wikipedia.org/wiki/ALS | reference | science, encyclopedia | 2026-05-05T11:04:10.701513+00:00 | kb-cron |
Neurodegeneration in ALS 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 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 cytoskeletal maintenance and axonal transport include DCTN1, PFN1, and TUBA4A. Several ALS genes encode 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 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 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 several 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 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 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 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 presynaptic neurons. However, it is unclear if this mechanism is responsible for its therapeutic effect.
== Diagnosis ==
No single test can provide a definite diagnosis of ALS. Instead, 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. Many biomarkers are being studied for the condition, but as of 2023 are not in general medical use. In the U.S., average time from first symptom to ALS diagnosis confirmation ranges from 11.5 to 15 months. Even though people with ALS may see 3-4 clinicians prior to referral to an ALS specialist for diagnosis confirmation, the bulk of the diagnostic delay in the U.S. may be while under the care of neurologist(s), particularly non-neuromuscular trained neurologists. The ALS Association assembled a "Time to Diagnosis" (T2D) workgroup composed of ALS specialists, pharmaceutical industry experts, and people with ALS to focus on developing solutions to reduce diagnostic delays. The T2D group developed and published the thinkALS tool, a clinical and referral instrument to increase confidence of early recognition of common ALS clinical features and streamlining referral processes to specialty ALS centers.