Understand ALS

The CDC ALS Dashboard currently projects 34,720 adults living with ALS in the United States in 2026. This is a population-level surveillance estimate, not an individual forecast, and estimates can change as data and methods are updated.

Amyotrophic lateral sclerosis, or ALS, is a neurodegenerative disease that affects nerve cells involved in voluntary muscle movement. As motor neurons become damaged, muscles can become weaker.

ALS can affect movement, speaking, swallowing, and breathing. The pattern of symptoms and the pace of change can differ from person to person.

ALS affects motor neurons in the brain and spinal cord that send signals to muscles used for voluntary movement. When these nerve cells are damaged, the muscles they control may become weak and may not work as they did before.

The effects can involve different parts of the body at different times. A clinical team looks at the person’s symptoms, examination, function, and changing needs rather than relying on one general pattern.

Motor neurons are nerve cells that carry movement signals from the brain and spinal cord to muscles. Upper motor neurons and lower motor neurons work together to support voluntary movement.

ALS affects motor-neuron systems. The terms used to describe those systems help clinicians describe findings, but a term by itself is not a diagnosis.

Possible symptoms include muscle weakness, muscle stiffness, cramps, or twitching. Weakness may begin in a limb or may first affect muscles used for speaking or swallowing.

Some people also experience changes involving breathing, thinking, behavior, or language. Symptoms are not identical for everyone, and other conditions can cause similar symptoms.

There is not one single test that confirms ALS in every person. A clinician considers the history, neurological examination, pattern of findings, and the results of tests used to evaluate the nervous system and rule out other conditions.

Diagnosis can take time because several conditions may resemble ALS. A qualified clinician, often with experience in neuromuscular disease, interprets the full clinical picture.

Some neurological, neuromuscular, spinal, metabolic, infectious, and other conditions can cause symptoms that overlap with ALS. This is one reason evaluation uses a medical history, examination, and appropriate testing.

A general list cannot determine what is happening for one person. Symptoms that are concerning or changing should be discussed with a qualified healthcare professional.

ALS is generally described as progressive, meaning that motor-neuron disease can lead to increasing weakness over time. Progression does not look exactly the same for every person.

The body region where symptoms begin, the functions affected, the pace of change, and the person’s goals all matter in care. A general description cannot predict an individual timeline.

Sporadic ALS usually describes ALS occurring without a known family history of ALS. It does not prove that genetics are not involved, and it does not mean that a person or family caused the disease.

Family histories can be incomplete or may not show the same condition across generations. Genetic information and family history are different kinds of information and should not be treated as interchangeable.

Familial ALS describes ALS occurring in a family pattern suggesting that more than one biological relative has been affected. A family pattern can be important context for genetic counseling and clinical care.

Familial does not mean that every person in a family will develop ALS, and a family history is not itself a genetic test result.

Genetic ALS describes ALS caused by a disease-causing genetic variant. Some genetic forms can be inherited, and several genes have been associated with ALS and with an ALS–frontotemporal dementia spectrum.

The meaning of a result depends on the specific variant, the evidence used to classify it, family history, and the person’s clinical context. Sporadic ALS, familial ALS, and genetic ALS are related terms but are not interchangeable.

Yes. A person can have ALS associated with a disease-causing genetic variant even when no family history is known. Family histories may be incomplete, relatives may have been undiagnosed, or a variant may be present without an obvious pattern in the family.

A genetic test result should be interpreted with appropriate counseling and clinical context. A result does not by itself predict when symptoms will begin, whether they will develop, or what an individual course will be.

Limb-onset ALS means that the first noticeable weakness begins in an arm, hand, leg, or foot. Someone may notice changes such as dropping objects, tripping, or difficulty with a movement they used to make easily.

A limb-onset description refers to where symptoms began. It does not, on its own, establish a diagnosis or predict how ALS will affect a person.

Bulbar-onset ALS means that early symptoms involve muscles used for speaking or swallowing. Changes may include speech that becomes less clear or difficulty managing food or liquids.

Speech or swallowing changes can have many causes. A qualified clinician evaluates the full set of symptoms and can help identify appropriate support.

Respiratory-onset ALS refers to ALS in which breathing-related symptoms are among the earliest recognized features. Breathing symptoms can also develop later as motor-neuron weakness changes.

Breathing concerns require prompt clinical attention. Respiratory testing and assessment by an experienced care team can help clarify what is happening and what support may be appropriate.

Some people with ALS experience changes in thinking, behavior, language, or executive functions. These changes can be subtle, can vary in type and severity, and may affect communication, decision-making, or daily support needs.

Cognitive or behavioral concerns should be discussed with the care team. They are part of the clinical picture, not a reason to make assumptions about a person’s abilities or wishes.

ALS and frontotemporal dementia, or FTD, can overlap in some people and families. The overlap may involve motor symptoms together with changes in behavior, personality, language, or other cognitive functions.

ALS–FTD is a spectrum description, not a statement that every person with ALS has dementia. Assessment and support should be individualized.

Sporadic ALS usually means ALS without a known family history. Familial ALS describes a family pattern. Genetic ALS describes ALS caused by a disease-causing genetic variant. These terms should not be used as if they mean the same thing.

A gene carrier is a person who has a particular genetic variant; the implications depend on the variant and the context. Presymptomatic means before observable symptoms relevant to the condition are present. Penetrance describes the proportion of people with a genetic variant who develop the associated trait or condition.

Can this page diagnose ALS? No. It provides educational information and source links; diagnosis requires individualized evaluation by qualified healthcare professionals.

Can a family history prove that ALS is genetic? No. Family history is important information, but it is not the same as a genetic test result.

Can a genetic result predict an individual future? A result may provide important information, but it does not by itself establish when symptoms will begin, whether symptoms will develop, or what care a person will need.

Myth: Sporadic ALS proves that genetics are not involved. Fact: “Sporadic” usually refers to the absence of a known family history; it does not prove that genetics are irrelevant.

Myth: Familial ALS and genetic ALS mean exactly the same thing. Fact: Familial describes a family pattern, while genetic describes disease caused by a disease-causing genetic variant.

Myth: A genetic result gives a personal timeline. Fact: A result needs professional interpretation and does not by itself predict an individual course.

Myth: One symptom or one test can confirm ALS. Fact: Diagnosis involves the full clinical picture and evaluation for other conditions.