Amyotrophic lateral sclerosis, or ALS, is a progressive neurodegenerative disease that destroys motor neurons, the nerve cells responsible for voluntary movement. As these neurons deteriorate, muscles weaken, waste away, and eventually stop working, leading to paralysis and, in most cases, death within a few years of diagnosis. The disease is sometimes called Lou Gehrig’s disease in the United States, after the baseball player who brought it to public attention in the 1930s. What makes ALS especially challenging is that the causes remain only partially understood, the diagnosis is still largely clinical, and available treatments extend survival by months rather than years.
How Symptoms Typically Begin
ALS does not look the same in everyone. Where symptoms first appear matters, because it affects how the disease is experienced, how quickly it is recognized, and how fast it progresses. In a study of 500 patients, roughly two-thirds first noticed problems in their limbs, about 29% started with difficulties in speech or swallowing, and a small fraction presented with breathing trouble as their first symptom.1PubMed Central. Clinical Course of Amyotrophic Lateral Sclerosis according to Initial Symptoms: An Analysis of 500 Cases
People with limb-onset ALS usually notice weakness or clumsiness in a hand or foot. Dropping things, stumbling, or having difficulty with fine motor tasks like buttoning a shirt are common early complaints. The weakness tends to start on one side and gradually spread. Muscle twitching and cramping often accompany the weakness, though twitching alone is extremely common in healthy people and is not a reliable sign of ALS.
Bulbar-onset ALS, which affects the muscles controlling speech and swallowing, tends to appear at a slightly older age. Slurred speech, a hoarse or nasal voice, difficulty chewing, and choking on food or liquids are typical early signs. This form is associated with a distinct pattern of brain involvement, including changes in regions linked to speech and language processing that are not seen in limb-onset cases.2PubMed Central. The neuropathological signature of bulbar-onset ALS: A systematic review
Respiratory-onset ALS is the rarest and most dangerous initial presentation. In the same study of 500 patients, all 21 people with respiratory-dominant onset were male, and over 70% required emergency intubation before they were even diagnosed with ALS.1PubMed Central. Clinical Course of Amyotrophic Lateral Sclerosis according to Initial Symptoms: An Analysis of 500 Cases Shortness of breath, especially when lying flat, and frequent respiratory infections may be the first clue. Because breathing problems have so many other possible explanations, the diagnosis is often delayed.
Cognitive and Behavioral Changes
ALS has historically been described as a disease that spares the mind while destroying the body. That picture turns out to be incomplete. More than half of people with ALS show some degree of cognitive or behavioral change, ranging from mild impairment in attention or word-finding to a full frontotemporal dementia syndrome.3PubMed Central. Amyotrophic lateral sclerosis – frontotemporal spectrum disorder (ALS-FTSD): Revised diagnostic criteria The deficits are heterogeneous and can include problems with social cognition, language, executive function, or personality.
This overlap between ALS and frontotemporal dementia is now recognized as a spectrum rather than two separate diseases. ALS and FTD share a common genetic cause in many families, and the same protein abnormalities show up in both conditions. For caregivers, the behavioral changes can be especially difficult to manage. A person with ALS may become apathetic, impulsive, or emotionally flat, and these shifts are caused by the disease, not by a change in attitude or effort.
What Goes Wrong Inside Motor Neurons
The hallmark of ALS at the cellular level is the death of both upper motor neurons in the brain and lower motor neurons in the spinal cord and brainstem. In the vast majority of cases, a protein called TDP-43 ends up in the wrong place inside the cell. Normally TDP-43 works in the nucleus helping manage RNA, but in ALS it clumps together in the surrounding cell body instead. This mislocation is found in about 97% of ALS cases and is considered one of the most consistent pathological features of the disease.4PubMed. Pathologically mislocalised TDP-43 in upper motor neurons causes a die-forward spread of ALS-like pathogenic changes throughout the mouse corticomotor system
Another process that contributes to motor neuron death is excitotoxicity. Glutamate is the main excitatory signaling molecule in the nervous system, and after a nerve impulse, it needs to be quickly cleared away by surrounding support cells called astrocytes. In ALS, this cleanup system breaks down: astrocyte glutamate transporters lose function, and the resulting buildup of glutamate overstimulates and damages motor neurons.5PubMed Central. Glutamate transporters and the excitotoxic path to motor neuron degeneration in amyotrophic lateral sclerosis This is the mechanism that riluzole, the first approved ALS drug, was designed to target.
The support cells themselves also become part of the problem. Astrocytes and microglia, which normally protect and nourish neurons, can shift into a toxic state as the disease progresses. Research in ALS mouse models has shown that knocking out three specific inflammatory factors released by microglia, which trigger toxic astrocyte conversion, markedly extended survival.6Nature Communications. Knockout of reactive astrocyte activating factors slows disease progression in an ALS mouse model The interaction between neurons and these supporting cells is now a major focus for developing future therapies.
Genetic and Environmental Risk Factors
About 5 to 10% of ALS cases run in families, a form called familial ALS. The remaining 90 to 95% are classified as sporadic, meaning no clear family history exists. But even sporadic ALS has a genetic component: dozens of genes have been linked to increased susceptibility, and the line between familial and sporadic cases is blurrier than it once seemed.
The single most common genetic cause of ALS in people of European ancestry is a repeat expansion in the C9orf72 gene, discovered in 2011. This same mutation is also the leading genetic cause of frontotemporal dementia, which helps explain the clinical overlap between the two diseases.7PubMed Central. Expanding Clinical Spectrum of C9ORF72-Related Disorders and Promising Therapeutic Strategies: A Review What complicates matters is that the mutation’s penetrance is variable: some carriers develop ALS in middle age, others much later, and some never develop symptoms at all.8PubMed Central. Amyotrophic lateral sclerosis caused by hexanucleotide repeat expansions in C9orf72: from genetics to therapeutics
Mutations in the SOD1 gene were the first identified genetic cause of ALS and remain among the most studied. Other genes implicated in familial ALS include TARDBP (the gene encoding TDP-43), FUS, and ANG. In one study of familial ALS patients, SOD1 mutations were found in 20%, FUS mutations in about 13%, and TARDBP mutations were rare.9PubMed. SOD1, ANG, VAPB, TARDBP, and FUS mutations in familial amyotrophic lateral sclerosis: genotype-phenotype correlations The specific gene involved can affect how the disease presents, at what age symptoms start, and how quickly it progresses.
On the environmental side, the evidence is more suggestive than conclusive. Military service is one of the most consistently studied risk factors. Veterans, particularly those deployed in the Gulf War and World War II, appear to have elevated ALS risk. Exposure to pesticides (including Agent Orange), heavy metals, exhaust fumes, and head trauma have all been linked to higher odds of developing ALS among military personnel.10PubMed Central. Military service, deployments, and exposures in relation to amyotrophic lateral sclerosis etiology Smoking, vigorous physical activity, and agricultural chemical exposure have been explored as possible risk factors in the general population, though proving causation remains difficult.11PubMed Central. Potential Environmental Factors in Amyotrophic Lateral Sclerosis
How ALS Is Diagnosed
There is no single blood test or imaging scan that definitively diagnoses ALS. The diagnosis remains clinical, based on a pattern of progressive weakness affecting both upper and lower motor neurons with no better explanation. For years the diagnostic criteria were complex, requiring evidence of disease spread across multiple body regions and the exclusion of a long list of mimics. The newer Gold Coast criteria simplify the process: they define ALS as progressive motor impairment with signs of both upper and lower motor neuron dysfunction in at least one body region, supported by electrophysiology findings and the absence of another disease that explains the symptoms.12PubMed Central. Diagnosing ALS: the Gold Coast criteria and the role of EMG
One of the most consequential mimics is multifocal motor neuropathy, or MMN, a rare immune-mediated condition that can look strikingly similar to ALS. Both cause progressive limb weakness and muscle wasting, but MMN is treatable with immune therapy, while ALS is not. Distinguishing between the two is critical, but the overlap in symptoms makes it challenging.13PubMed Central. The Potential Misdiagnosis of Multifocal Motor Neuropathy as Amyotrophic Lateral Sclerosis-A Case Series Newer blood-based biomarkers, particularly neurofilament light chain (NfL), are showing promise in separating the two. In one study, serum NfL levels were nearly three times higher in ALS patients compared to those with MMN, and the test distinguished the two groups with very high accuracy.14PubMed. Multifocal motor neuropathy as a mimic of amyotrophic lateral sclerosis: Serum neurofilament light chain as a reliable diagnostic biomarker
Diagnostic delay remains a real problem. The average time from first symptoms to a confirmed ALS diagnosis is roughly a year, and many people see multiple specialists before arriving at the answer. Part of the delay is inherent in the nature of the disease: early symptoms are nonspecific, and the diagnosis depends on observing progression over time. Part of it is that doctors must first rule out treatable conditions that can present similarly.
Blood Biomarkers and Prognosis
Beyond helping with diagnosis, NfL has emerged as a useful prognostic marker. Neurofilaments are structural proteins inside nerve cells, and when neurons are damaged, neurofilament fragments spill into the cerebrospinal fluid and blood. People with ALS have blood NfL levels roughly four times higher than healthy individuals, and these levels tend to remain elevated throughout the disease.15PubMed Central. Neurofilament light chain: A prognostic biomarker in amyotrophic lateral sclerosis Higher NfL levels at the time of diagnosis are independently linked to shorter survival. Patients in the highest third of baseline NfL had nearly four times the mortality risk compared to those in the lowest third.15PubMed Central. Neurofilament light chain: A prognostic biomarker in amyotrophic lateral sclerosis
Another protein being studied alongside NfL is glial fibrillary acidic protein (GFAP), a marker of astrocyte activation. Serum levels of both NfL and GFAP are significantly elevated in ALS patients and appear to correlate with how long someone has been living with the disease.16Scientific Reports. Correlation analysis of serum neurofilament light chain and glial fibrillary acidic protein levels with amyotrophic lateral sclerosis These biomarkers are not yet standard in routine clinical practice for all patients, but they are increasingly used in clinical trials to measure whether a therapy is reducing nerve damage, which gives researchers a faster signal than waiting for clinical decline.
Approved Treatments
Three drugs have been approved for ALS, and it is worth being honest about what they can and cannot do. None of them cures the disease. Two are broadly applicable, and the third targets a small genetic subset.
Riluzole, approved in the mid-1990s, works by reducing glutamate signaling, addressing the excitotoxicity mechanism described above. It was the only approved ALS drug for over two decades. Clinical trials initially showed a survival benefit of roughly two to three months, though more recent real-world analyses suggest the benefit may be larger.17PubMed. Riluzole and edaravone: A tale of two amyotrophic lateral sclerosis drugs Riluzole does not reverse symptoms or halt progression, but it is the backbone of ALS pharmacotherapy and is well tolerated by most people.
Edaravone, an antioxidant, was approved in 2017 after a trial showed it slowed the rate of functional decline in a selected group of early-stage ALS patients.17PubMed. Riluzole and edaravone: A tale of two amyotrophic lateral sclerosis drugs The benefit was modest, and the drug is most likely to help people who are still in the early stages of disease. It is now available as an oral formulation, which is far more practical than the original intravenous version that required frequent infusion sessions.
Tofersen, the most recently approved treatment, represents a fundamentally different approach. It is an antisense oligonucleotide, a synthetic strand of genetic material designed to attach to the messenger RNA produced by the SOD1 gene and trigger its destruction, thereby reducing the production of the toxic SOD1 protein.18PubMed. Phase 1-2 Trial of Antisense Oligonucleotide Tofersen for SOD1 ALS Tofersen is only indicated for patients with confirmed SOD1 mutations, which account for a small percentage of all ALS cases. In the phase III trial, tofersen reduced levels of SOD1 protein in cerebrospinal fluid and lowered blood neurofilament levels, a sign that neuronal damage was slowing. Clinical differences were modest during the initial 28-week trial period, but patients who started treatment earlier fared measurably better than those who began later in the open-label extension, with a difference of about 3.5 points on the ALS functional rating scale at one year.19PubMed. Trial of Antisense Oligonucleotide Tofersen for SOD1 ALS The drug is administered by lumbar puncture, and spinal-tap-related side effects are common.
Multidisciplinary Care and Symptom Management
While drug treatments for ALS are limited, the overall management of the disease has a measurable impact on how long and how well people live with it. Multidisciplinary clinics that bring together neurologists, respiratory therapists, speech pathologists, nutritionists, physical therapists, and social workers in coordinated visits have been shown to extend survival. One study found that patients managed in a multidisciplinary setting gained roughly six additional months of survival, with the benefit largely driven by earlier and more consistent use of noninvasive ventilation and feeding tube placement.20PubMed Central. Survival benefit of multidisciplinary care in amyotrophic lateral sclerosis in Spain: association with noninvasive mechanical ventilation
Noninvasive ventilation, typically a bilevel positive airway pressure (BiPAP) device, is one of the most impactful interventions available. It supports breathing without requiring a surgical procedure, improves sleep quality, reduces fatigue, and extends life. Getting the timing right matters: studies consistently find that multidisciplinary teams improve access to ventilation and increase the likelihood that patients accept and stick with it.21European Respiratory Journal. The optimisation of noninvasive ventilation in amyotrophic lateral sclerosis: a systematic review
Nutrition is another area where early planning pays off. As bulbar muscles weaken, swallowing becomes unsafe, and people lose weight rapidly. Gastrostomy tubes, placed through the abdominal wall directly into the stomach, maintain caloric intake and reduce the risk of aspiration pneumonia. Bulbar impairment can lead to choking, laryngospasm, and malnutrition, all of which drive emergency room visits that could be reduced with earlier intervention.22PubMed. Emergencies in Amyotrophic Lateral Sclerosis
Other supportive measures include medications for excessive saliva production, muscle cramps, and emotional lability (a condition where people laugh or cry uncontrollably and inappropriately, common in ALS). Communication devices become essential as speech deteriorates, and many people now use eye-tracking technology to operate computers and communicate with their families.
Stem Cells and Experimental Approaches
Stem cell therapy is one of the most frequently asked-about experimental approaches in ALS. The concept is appealing: replace or protect dying motor neurons using transplanted cells. But the reality is that clinical trials remain in early stages. Reviews of these trials have found that while several approaches have shown acceptable safety, the field has not yet determined the right type of cell, the right dose, the best delivery method, or the ideal treatment window.23PubMed Central. Stem cell treatments for amyotrophic lateral sclerosis: a critical overview of early phase trials Some trials involve invasive procedures like spinal cord injections, raising ethical questions about how to design appropriate sham controls for patients in the comparison group.
Beyond stem cells, the antisense oligonucleotide approach used in tofersen has inspired similar strategies targeting other ALS genes. Researchers are also investigating treatments that address the TDP-43 protein buildup seen in the vast majority of cases, which would be relevant to a far larger share of patients than the SOD1-focused tofersen. Gene therapy, immunotherapy, and drugs aimed at the toxic astrocyte and microglia pathways are all active areas of investigation. The biomarker progress covered earlier is accelerating these efforts, because measuring NfL levels gives clinical trialists a way to detect whether a drug is protecting neurons long before enough time has passed to observe clinical differences.
People with ALS are sometimes approached with offers of unproven treatments, particularly stem cell procedures marketed overseas. These can be expensive, carry real risks, and operate outside the regulatory framework that protects patients in clinical trials. Anyone considering an experimental therapy should discuss it with their neurologist and check whether a legitimate clinical trial exists through registries like ClinicalTrials.gov.