What is the typical age of onset for ALS?

The average age of onset for ALS is 55 years. However, the disease is very rare before the age of 18 and after the age of 80. Early-onset ALS (before the age of 18) is particularly rare. Onset after age 80 is unusual, but not as rare as the juvenile forms of ALS. Onset before age 25 is referred to as “juvenile ALS” (JALS) (“juvenile” can be translated as “youthful”). Onset between the ages of 25 and 40 is called “early adult ALS” (“adult” can be translated as “grown-up”). This term is used to emphasize that, in this case, ALS occurs before the typical middle adult years.

Juvenile and early-onset adult ALS are characterized by specific clinical features. In early-onset adult ALS, flaccid paralysis (paresis) and muscle wasting (myopathy) of the arms, combined with stiffness (spasticity) of the legs, are particularly common. This course of the disease is also seen in juvenile ALS (JALS). However, the variability in the course of JALS is very high. For example, a chronic form of JALS is known, with a typical disease duration of 20–30 years. The most well-known patient with chronic JALS was the astrophysicist Stephen Hawking. In contrast to chronic JALS, an acute form of the disease is also known, which progresses at a particularly rapid rate. In acute JALS, flaccid paralysis and pronounced muscle atrophy occur in rapid succession, along with involvement of the respiratory muscles. Acute JALS can lead to death within a few months—or necessitate mechanical ventilation.