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Genetic Factors in ALS (Lou Gehrig's Disease) Explained

Amyotrophic lateral sclerosis (ALS), often called Lou Gehrig’s disease, is a progressive neurodegenerative disorder that destroys the motor neurons controlling voluntary muscle movement. About 90% of cases are sporadic, with no clear family history, while roughly 10% are familial and inherited. Even in sporadic cases, genetics contributes to risk. Decades of research have identified specific genes that, when mutated, drive motor-neuron degeneration — reshaping how scientists understand the disease.

Familial versus sporadic ALS

Roughly one in ten people with ALS have a family history, usually inherited in an autosomal-dominant pattern, meaning a single altered copy of a gene can be enough to raise risk. The remaining cases are sporadic. The line between the two is blurry: some people with “sporadic” ALS carry known risk variants, and the same genes appear in both groups. Understanding the genetics helps explain a disease that otherwise seems to strike at random.

C9orf72: the most common genetic cause

The single most common genetic cause of ALS is a repeat expansion in C9orf72. Healthy individuals carry a short hexanucleotide (GGGGCC) repeat; affected individuals can carry hundreds to thousands. This expansion accounts for a large share of familial ALS and a meaningful portion of sporadic cases, and it also links ALS to frontotemporal dementia — the two conditions can appear in the same families, part of an ALS-FTD spectrum.

SOD1: the first ALS gene discovered

The first gene tied to ALS was SOD1, which encodes superoxide dismutase 1, an antioxidant enzyme. Mutations were identified in 1993 and remain a major cause of familial ALS. SOD1 mutations are thought to make the protein toxic through a gain of function rather than simply losing its antioxidant role. SOD1 has become central to research, including therapies designed to lower the mutant protein in carriers.

TARDBP, FUS, and the RNA-processing story

TARDBP encodes TDP-43, a protein that clumps abnormally in the motor neurons of the great majority of ALS cases regardless of cause — making it a unifying hallmark of the disease. FUS encodes a related RNA-binding protein, and its mutations tend to cause earlier-onset disease. Together, C9orf72, SOD1, TARDBP, and FUS point to disrupted RNA processing and protein handling as core drivers of motor-neuron death.

What genetic knowledge does and does not offer

Genetic testing in ALS is done through neurology and genetic-counseling channels, and it carries weight: results affect family members, eligibility for gene-targeted clinical trials, and difficult personal decisions. Carrying a variant does not guarantee disease, and most people with a family variant will want formal counseling before testing. Consumer pathway-level insight is not a substitute for this specialized clinical process.

What pathway-level genetic insight adds

The PlexusDx Precision Peptide Genetic Test analyzes 14 pathways, 49 peptides, 150+ genetic insights across biological pathways relevant to general wellness. It is an educational tool that describes your biology at the pathway level — it does not test for ALS-causing mutations, diagnose neurodegenerative disease, or predict who will develop ALS. PlexusDx tells you about your biology; it does not tell you what to put in your body. Anyone concerned about inherited ALS risk should work with a neurologist and a certified genetic counselor.

Frequently Asked Questions

Is ALS inherited?

About 10% of ALS is familial and inherited, usually in an autosomal-dominant pattern, while roughly 90% is sporadic with no clear family history. Even sporadic cases can involve genetic risk variants. Inheriting a known ALS gene raises risk but does not guarantee the disease will develop.

What is the most common ALS gene?

A repeat expansion in C9orf72 is the most common genetic cause of ALS, accounting for a large share of familial cases and some sporadic ones. Other major genes include SOD1, the first discovered, plus TARDBP (TDP-43) and FUS, which affect RNA processing in motor neurons.

Can a genetic test predict whether I will get ALS?

No. Even carrying a known ALS variant does not guarantee disease, and testing is complex. ALS genetic testing is done through neurology and genetic counseling, never as a stand-alone prediction. A pathway-level wellness test cannot diagnose ALS or forecast who will develop it.

Should I get genetic counseling for ALS?

If you have a family history of ALS or frontotemporal dementia, yes. Certified genetic counselors and neurologists help you weigh whether testing is right for you, interpret results, and consider effects on relatives. Because results carry deep personal implications, professional counseling should always come first.

Curious how your own biology maps to these pathways? Take the Precision Peptide Genetic Test to see the pathway-level genetic context behind your results, then bring it to a qualified provider who knows your full picture.

This article is part of the PlexusDx Education Hub. Browse all Brain & Cognitive Health education

The Precision Peptide Genetic Test analyzes how your genes influence peptide-related biological pathways. It does not recommend, prescribe, or determine which peptides you should use. Consult a qualified healthcare provider before beginning any peptide protocol.