Amyotrophic lateral sclerosis (ALS) affects the nerve cells in the brain and spinal cord that control muscle movement. Different types of ALS cause symptoms to begin in a certain part of the body and eventually progress to other areas.

Amyotrophic lateral sclerosis (ALS) is a group of progressive neurological diseases also known as Lou Gehrig’s disease. It affects the motor neurons, the nerve cells in the brain and spinal cord that control voluntary muscle movement and breathing.

ALS leads to muscle weakness, loss of mobility, and eventually, respiratory failure. Understanding the different types of ALS, their prevalence, and their causes is important for early diagnosis and treatment.

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Sporadic ALS accounts for approximately 90% to 95% of all cases worldwide, making it the most common type. It occurs without any known family history and can affect anyone, regardless of age or background, though it is more common in individuals ages 40 to 70 years.

The precise causes of sporadic ALS remain unclear however, doctors believe a combination of genetic, environmental, and lifestyle factors may contribute. Approximately 1% of sporadic ALS cases are due to a genetic mutation in the SOD1 gene. Other potential risk factors include:

Familial ALS (FALS) is a genetic form of ALS, meaning individuals inherit it. It accounts for approximately 10% of ALS cases, making it less common than sporadic ALS.

Genetic mutations cause FALS, producing toxic proteins or impairing cellular processes that damage motor neurons. Most cases follow an autosomal dominant pattern, meaning a child of an affected parent has a 50% chance of inheriting the mutation; however, inheriting a mutation does not always result in ALS. The most common mutations linked to FALS are in the C9ORF72 and SOD1 genes.

FALS often occurs at a younger age than sporadic ALS. Symptoms and progression can vary, and those who do not inherit the mutation cannot pass it to any children they may have.

ALS-Parkinsonism dementia complex (ALS-PDC) is a rare type of ALS involving an abnormal buildup of tau tangles and protein clusters, distinguishing it from other neurodegenerative diseases such as Alzheimer’s disease.

Researchers first identified ALS-PDC in the Chamorro population of Guam. Though they have not determined the exact cause, they suspect exposure to toxins in cycads, a traditional food, may play a role, as cases have decreased due to dietary and lifestyle changes.

Juvenile ALS (JALS) is a rare form of the disease that begins before the age of 25. About 40% of cases are linked to specific gene mutations, with the most common being:

  • FUS
  • SETX
  • ALS2

Doctors should check for genetic mutations in young people with motor neuron problems, as hereditary patterns and other symptoms can help predict how the disease will progress.

FTD refers to a group of disorders that cause a change to the frontal lobes of the brain, which are associated with personality, language, and behavior. When FTD and ALS occur together, a subtype of ALS called ALS-FTD results.

Although FTD and ALS are separate conditions, a 2024 article notes that ALS is closely related to FTD. Up to 50% of those with a motor neuron disease, like ALS, develop behavioral symptoms, and 10% to 15% meet the criteria for FTD.

The most common genetic cause associated with both conditions affects the C9orf72 gene.

The following outlines the types of ALS based on the classification of clinical onset.

Limb onset ALS

Limb onset ALS begins with symptoms such as muscle weakness in the arms or legs. Other symptoms may include:

  • difficulty walking
  • tripping
  • having difficulty with fine motor tasks

Symptoms often start in one limb and then spread to the opposite limb, followed by the other limb on the same side, and finally, the last limb. Over time, the disease affects the muscles used for speech, swallowing, and breathing.

Bulbar-Onset ALS

Bulbar-onset ALS symptoms begin in the neck or face. The name comes from the “bulbar” region of the brain that controls the muscles in the face and neck and processes such as swallowing and speech. Symptoms of bulbar-onset ALS include:

  • slurred speech
  • difficulty chewing and swallowing
  • choking
  • weakness or twitching in the face and neck

Bulbar onset ALS occurs more often in older adults and people with cognitive impairment. Symptoms often progress more rapidly than other types, affecting other parts of the body and eventually leading to paralysis.

Doctors consider bulbar-onset ALS to be one of the most aggressive forms of ALS due to its rapid progression and early impact on critical functions like swallowing and speaking.

The average life expectancy for someone with ALS is 3 to 5 years from when the symptoms first appear. However, some individuals can live significantly longer, with 10% surviving 10 years or more.

The most common first symptom of ALS is gradual progression on muscle weakness or stiffness. Limb-onset ALS frequently begins with difficulty walking or performing fine motor tasks whereas bulbar onset ALS symptoms may include difficulty swallowing.

Sporadic ALS is the most common type of ALS, accounting for approximately 90% to 95% of all cases.

The classification of ALS remains consistent throughout the disease course. However, symptoms and affected areas may evolve as the disease progresses.

ALS is a group of progressive neurodegenerative disorders that affect motor neurons in the brain and spinal cord, leading to muscle weakness, loss of mobility, and eventually respiratory failure. ALS is categorized into several types based on genetic and environmental factors, as well as the location of initial symptoms.

Sporadic ALS is the most common type and occurs without a known family history, while individuals inherit familial ALS (FALS), which is linked to specific genetic mutations. ALS can also be classified by clinical onset, with limb-onset ALS starting in the arms or legs and bulbar-onset ALS affecting the face and neck.