What is ALS?

ALS Defined: The Direct Answer to Your Question

ALS is a progressive neurodegenerative disease affecting motor neurons

ALS (amyotrophic lateral sclerosis) is a disease of the nervous system that attacks motor neurons -- the nerve cells in your brain and spinal cord responsible for controlling how your muscles move. [1] These neurons govern every voluntary movement, from walking and breathing to speaking and swallowing, so when they break down, the muscles they control gradually weaken and waste away. [2] ALS is fatal and currently has no cure, though research into new therapies is ongoing. [1] Also known as Lou Gehrig's disease, ALS progresses at different speeds for different people, but understanding [what ALS does to the body](https://alsunited.org/blog/what-is-als-and-how-als-affects-your-body) always starts in the same place: the slow, irreversible loss of motor neuron function. [1]

How ALS differs from other neurological conditions

ALS is often confused with other neurological conditions, but the differences in how each affects the nervous system are significant. Parkinson's disease targets dopamine-producing cells in the basal ganglia -- the brain region that coordinates movement -- causing tremors, rigidity, and balance problems that are distinct from ALS's progressive muscle weakness and wasting.[3] Both conditions worsen over time and have no cure, but ALS progresses faster and is always fatal, typically within three to five years, whereas Parkinson's disease does not directly cause death and many people maintain a near-typical life expectancy with treatment.[4] Our [ALS vs. MS overview](https://alsunited.org/blog/als-vs-ms-key-differences-and-similarities/) covers how ALS compares to additional neurological diseases for anyone seeking a broader picture.

Why early understanding matters for diagnosis and support

ALS patients wait an average of 10 to 16 months from first symptoms to a confirmed diagnosis, and that delay directly postpones access to multidisciplinary care shown to improve survival and quality of life. [5] Several factors drive this gap: early symptoms like hand weakness or foot drop closely mimic more common conditions, most primary care providers see only one or two ALS cases in their entire careers, and misdiagnosis occurs in 13 to 68% of cases before the correct diagnosis is reached. [5] Knowing what ALS is -- and recognizing its first warning signs -- gives patients and families more time for specialized care, informed planning, and decisions about treatment and daily life. [6]

What Happens in the Body: The Progression of Motor Neuron Damage

How upper and lower motor neurons break down over time

In ALS, two types of motor neurons break down at the same time: upper motor neurons in the brain's motor cortex, and lower motor neurons in the brainstem and spinal cord. [7] Upper motor neuron damage produces spasticity and heightened reflexes, while lower motor neuron loss causes the muscle weakness and wasting most closely associated with ALS. [7] Both sets of neurons degenerate progressively, cutting off the electrical signals that tell muscles when and how to move -- a process that cannot currently be stopped or reversed. [8] This dual breakdown helps explain why ALS symptoms can vary from person to person depending on which neurons are affected first. [7]

What happens to muscles as ALS progresses

As motor neurons lose function, the muscles they control begin to weaken, shrink, and eventually waste away -- a process called denervation atrophy. [9] Weakness typically starts in one area, such as a hand or foot, then spreads to adjacent muscles over time, often creating visible asymmetry in the arms or legs. [10] Muscle twitches called fasciculations are common as nerves deteriorate, and affected limbs may feel cold or achy, though ALS does not cause numbness or sensory loss. [9] As [the disease moves through its stages](https://alsunited.org/blog/the-7-stages-of-als-how-they-could-be-broken-down), this progressive weakness eventually leads to paralysis, and most people with ALS lose the ability to move, speak, swallow, and breathe independently. [9]

Why muscle weakness and paralysis occur in ALS

The connection between motor neurons and muscles depends on a constant flow of electrical signals -- when motor neurons degenerate, that signal chain breaks down entirely, leaving muscles with no instructions to contract or move. [11] Without those signals, muscles cannot respond on command, which is the direct cause of the progressive weakness and eventual paralysis that define ALS. [11] Cellular defects involving protein recycling, gene regulation, and structural damage within motor neurons are among the mechanisms researchers believe drive this degeneration, though the exact trigger remains unclear in most cases. [11] As more neurons are lost and the signal interruption spreads, voluntary movement becomes increasingly impossible -- a process that ultimately affects breathing, since the muscles controlling the diaphragm rely on the same motor neuron pathways. [12]

Types of ALS: Sporadic, Familial, and Regional Variants

Sporadic ALS accounts for 90% of cases with no family history

Sporadic ALS accounts for roughly 90% of all ALS cases and occurs in people with no known family history of the disease. [13] Genetics still appear to play a role, however: about 10% of sporadic cases carry a known disease-associated mutation, with C9ORF72 and SOD1 being the most commonly identified genes. [13] In most cases, no specific mutation is found, and the leading hypothesis is that a combination of genetic variations and environmental exposures -- including smoking, pesticide exposure, and traumatic injury -- interact to increase disease risk. [14] People with sporadic ALS typically develop first symptoms between ages 58 and 63, slightly later than the 40-to-60 range seen in [familial ALS](https://alsunited.org/blog/does-als-run-in-families/). [13]

Familial ALS: genetic inheritance patterns and risk factors

Familial ALS is confirmed when the disease affects more than one person in the same biological family; a specific disease-associated mutation can be found in roughly two-thirds of those cases, spanning more than 40 known genes. [16] The vast majority of these mutations follow an autosomal dominant inheritance pattern -- one altered gene copy is enough to trigger disease, giving each biological child of a carrier a 50% chance of inheriting it. [17] Many of these mutations also carry reduced penetrance, meaning not everyone who inherits a mutation will develop ALS during their lifetime, a complexity explored in our overview of the [familial ALS inheritance pattern](https://alsunited.org/blog/familial-als-inheritance-pattern). [15] First symptoms in familial ALS typically appear between ages 40 and 60, roughly a decade earlier than the late-50s onset seen in sporadic cases. [16]

Regional variants including bulbar and limb-onset ALS

Where ALS begins determines how it progresses and how long someone typically lives with it. About 70% of people develop limb-onset ALS, with first symptoms appearing in the hands, arms, or legs, while roughly 25% develop bulbar-onset ALS, which affects the motor neurons controlling speech and swallowing. [18] Bulbar-onset ALS progresses faster than limb-onset: patients typically survive less than two years from diagnosis, partly because bulbar weakness raises the risk of aspiration and makes breathing support harder to tolerate. [6] Our overview of [bulbar ALS](https://alsunited.org/blog/understanding-bulbar-als) covers what those early speech and swallowing changes look like and how care teams respond as the disease advances.

First Warning Signs and Getting a Diagnosis

Early ALS symptoms: muscle twitches, weakness, and speech changes

The first warning signs of ALS are typically painless -- gradual muscle weakness in one hand, foot, or leg, sometimes accompanied by visible muscle twitching called fasciculations. [12] Weakness usually appears on one side of the body first and shows up as difficulty gripping objects, dropping things, or catching a toe when walking, which doctors call foot drop. [10] For a smaller share of people, early symptoms involve the muscles controlling speech and swallowing instead, producing slurred speech or difficulty swallowing before any limb weakness appears. [10] Because these signs closely mimic carpal tunnel syndrome or a pinched nerve, many people won't suspect ALS until symptoms spread to an adjacent muscle group -- our overview of [very early ALS symptoms](https://alsunited.org/blog/very-early-als-symptoms-what-to-look-out-for) covers what to watch for before a diagnosis is confirmed. [10]

How doctors diagnose ALS using clinical tests and imaging

Diagnosing ALS requires ruling out other conditions first, since no single test confirms the disease on its own.[19] The two most important tools are an EMG (electromyography) -- which detects abnormal electrical activity in muscles through nerve conduction studies and a fine-needle examination -- and an MRI of the neck and spine, which rules out structural causes like herniated discs, tumors, or spinal cord compression.[20][21] Blood tests screen for conditions that mimic ALS, including thyroid disease, vitamin B12 deficiency, and autoimmune disorders, while genetic testing is typically reserved for people with a family history of the disease.[21] Neurologists apply the El Escorial criteria to classify diagnostic certainty, requiring evidence of both upper and lower motor neuron damage across multiple body regions before confirming a diagnosis -- a process explored further in our overview of [ALS diagnosis steps](https://alsunited.org/blog/als-diagnosis-steps-to-confirming-the-condition/).[20]

Why connecting with ALS United support begins at diagnosis

The first year after an ALS diagnosis is the most consequential for treatment access: patients survive an average of 30 months after diagnosis, and most clinical trials restrict enrollment to people diagnosed within the past two years. [23] Multidisciplinary care -- combining neurologists, physical therapists, respiratory specialists, and social workers -- has been shown to extend survival and quality of life, but existing therapies cannot restore function already lost, which is why early connection matters. [22] Our [care services](https://alsunited.org/blog/our-care-services) are built to link newly diagnosed patients with specialized clinics and support networks from day one -- because we are here for you, and the earlier that connection happens, the more options stay open. [23]