How ALS Attacks the Body—and Why It's So Hard to Stop
Amyotrophic lateral sclerosis destroys motor neurons that control voluntary movement, leaving patients progressively paralyzed. Here's how the disease works, what causes it, and where treatment stands.
What Is ALS?
Amyotrophic lateral sclerosis (ALS), also known as Lou Gehrig's disease or motor neuron disease, is a progressive neurodegenerative condition that destroys the nerve cells responsible for voluntary movement. As motor neurons in the brain and spinal cord die, muscles weaken, waste away, and eventually stop working entirely. The disease is always fatal, with an average survival of two to four years from symptom onset, though roughly 10% of patients live longer than a decade.
ALS affects an estimated 5 per 100,000 people worldwide each year. It typically strikes between ages 55 and 75 and is about 20% more common in men, according to the National Institute of Neurological Disorders and Stroke.
How Motor Neurons Die
The hallmark of ALS is the degeneration of both upper motor neurons (in the brain) and lower motor neurons (in the brainstem and spinal cord). Upper motor neurons send signals down the spinal cord; lower motor neurons relay those signals to muscles. When both types fail, patients lose the ability to walk, speak, swallow, and ultimately breathe.
No single mechanism explains why motor neurons are so vulnerable. Research points to a toxic combination of factors working simultaneously:
- Glutamate excitotoxicity — ALS patients have abnormally high levels of glutamate, a chemical messenger that overstimulates and kills nerve cells when present in excess.
- Protein misfolding — Misshapen proteins, particularly TDP-43, accumulate inside neurons, disrupting normal cell function and triggering cell death.
- Mitochondrial dysfunction — The cellular power plants that produce energy malfunction, starving motor neurons of the fuel they need.
- Neuroinflammation — Glial support cells that normally protect neurons instead become overactive and contribute to damage.
These mechanisms create a cascading failure: once one system breaks down, it accelerates the collapse of others, making the disease almost impossible to reverse once it gains momentum.
What Causes ALS?
About 90% of ALS cases are sporadic, meaning they appear without a clear family history. The remaining 10% are familial, caused by inherited genetic mutations. More than a dozen genes have been linked to ALS, but two dominate: mutations in the C9orf72 gene account for 25–40% of familial cases, while SOD1 mutations cause another 12–20%, according to the Mayo Clinic.
Environmental factors likely play a role in sporadic cases. Exposure to heavy metals, pesticides, and military service have been flagged as possible risk factors, though no single environmental trigger has been definitively proven. Recent research from Case Western Reserve University has identified gut bacteria as a potential environmental trigger—harmful sugars produced by certain microbes can spark immune responses that damage motor neurons, particularly in people carrying the C9orf72 mutation.
Why ALS Is So Difficult to Treat
ALS attacks through multiple pathways simultaneously, which means blocking one mechanism rarely slows the overall disease. The blood-brain barrier also limits which drugs can reach motor neurons. Diagnosis itself is a challenge—there is no single definitive test for ALS, and patients often wait 12 months or more from first symptoms to confirmed diagnosis, losing precious treatment time.
Only a handful of drugs have been approved. Riluzole, available since 1995, modestly reduces glutamate toxicity and extends survival by a few months. Edaravone, approved in 2017, acts as an antioxidant but shows limited benefit in later-stage patients. More recently, gene therapies targeting specific mutations—such as tofersen for SOD1-ALS—have shown promise, with some patients experiencing stabilized symptoms over three years of treatment, according to University of Utah Health.
Where Research Stands
The treatment landscape is shifting. Gene therapies and vectorized antibodies targeting TDP-43 protein aggregation are entering clinical trials. Over 160 randomized clinical trials for ALS are currently ongoing or planned worldwide. The HEALEY ALS Platform Trial, running across 80 U.S. sites, tests multiple experimental drugs simultaneously to accelerate the search for effective treatments.
The gut-brain connection adds another potential avenue: if specific bacterial triggers can be identified and neutralized, it might be possible to prevent ALS in genetically at-risk individuals before symptoms ever appear. For a disease that has resisted treatment for over a century, that prospect—stopping ALS before it starts—represents a fundamentally new strategy.
