Neurology / neurodegenerative disease · BEGINNER LESSON
Amyotrophic lateral sclerosis
Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease with loss of upper and lower motor neurons, causing weakness, spasticity, and muscle wasting. It was first defined from clinic and pathology together, and is now understood to affect more than the motor system in many patients.
What ALS is and what is measured
Amyotrophic lateral sclerosis (ALS) is a disease in which upper motor neurons and lower motor neurons degenerate. Upper motor neurons begin in the motor cortex of the brain and help control movement; lower motor neurons connect the brainstem and spinal cord to muscles. Doctors and researchers measure clinical signs such as muscle weakness, muscle wasting or atrophy, spasticity, fasciculations, swallowing problems, speech problems, and breathing failure, because these show how the nervous system and muscles are being affected. In its original description, ALS was recognized by the combination of weakness, atrophy, spasticity, and degeneration of the lateral corticospinal tracts. [0,1,2]
[1] Amyotrophic lateral sclerosis (ALS): new insights 156 years ... [2] pmc.ncbi.nlm.nih.gov › articles › PMC12941290Amyotrophic Lateral Sclerosis (ALS) Genetics and Microbiota ... [3] Introduction to the Supplement - PMC - NIH
How the disease develops
The excerpts describe ALS as a progressive disorder driven by more than one biological process. Reported mechanisms include oxidative stress, which means harmful imbalance from reactive oxygen species; glutamate-mediated excitotoxicity, which means damage from excessive excitatory signaling; mitochondrial dysfunction, which means failure of the cell structures that help make energy; protein aggregation, including TDP-43 proteinopathy; axonal transport defects; RNA metabolism problems; and neuroinflammation. Genetic changes mentioned in the sources include C9orf72, TARDBP, FUS, SOD1, NEK1, and ATXN2. These processes help explain why motor neurons are especially vulnerable. [0,1,2]
[1] Amyotrophic lateral sclerosis (ALS): new insights 156 years ... [2] pmc.ncbi.nlm.nih.gov › articles › PMC12941290Amyotrophic Lateral Sclerosis (ALS) Genetics and Microbiota ... [3] Introduction to the Supplement - PMC - NIH
Why ALS is now seen as broader than a motor disease
Early work focused on the motor system because that was what could be seen clinically and anatomically. Newer evidence shows that ALS can also involve cognition, behavior, autonomic function, and sometimes sensory or affective symptoms. The sources report cognitive changes in about half of patients and frontotemporal dementia in a smaller subset, so ALS is now described as a multisystem neurodegenerative disorder rather than a purely motor one. [0,1]
[1] Amyotrophic lateral sclerosis (ALS): new insights 156 years ... [2] pmc.ncbi.nlm.nih.gov › articles › PMC12941290Amyotrophic Lateral Sclerosis (ALS) Genetics and Microbiota ...
Limitations of current understanding and treatment
The exact cause of ALS is not fully understood, and the disease is heterogeneous, meaning it does not look the same in every person. The excerpts also note that approved medicines do not halt or reverse progression, and that some evidence comes from limited models such as one patient-derived cell study. This means the biology is still being worked out, and findings from one mutation, one cell line, or one subgroup may not apply to all patients with ALS. [1,2]
[2] pmc.ncbi.nlm.nih.gov › articles › PMC12941290Amyotrophic Lateral Sclerosis (ALS) Genetics and Microbiota ... [3] Introduction to the Supplement - PMC - NIH
SEE THE IDEA
How ALS is described in the sources
These neurons degenerate in the brain and spinal cord.
Oxidative stress, excitotoxicity, mitochondrial problems, and mutations such as SOD1 or TARDBP contribute.
Weakness, atrophy, spasticity, fasciculations, and later swallowing or breathing problems appear.
Some patients also show cognitive, behavioral, or autonomic changes.
The disease starts with neuronal degeneration and interacting cellular problems, which produces movement symptoms and, in many patients, broader nervous system involvement.
ALS links cell-level injury to progressive movement loss, and in many cases to more than motor symptoms.
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Sources and further reading
This general lesson was generated from public source material. It explains a concept; it does not interpret a private paper or provide medical advice.