What are variants and “phenotypes” of ALS?

ALS is a complex and individual disease in which the symptoms
and their progression over time vary greatly. This “heterogeneity” (diversity) is a central feature of the disease and manifests itself in different variants and particular courses, which are referred to as “phenotypes”. “Phenotype” is a medical word from the Greek, which can be described as follows: Appearance of a disease, symptom pattern or disease expression.

In ALS, the phenotype is determined by three factors: 1) location of symptom onset – ALS can begin in different parts of the body, in the speech and swallowing muscles, arms, legs or respiratory muscles; 2) propagation – the speed and direction in which motor symptoms spread from the initial location to other parts of the body; and 3) the extent of motor neuron symptoms – ALS can affect the first motor neuron and/or the second motor neuron to varying degrees.

These differences in phenotype influence the sequence of symptoms as well as progression and survival time. Some forms of ALS progress more slowly, while others show more rapid progression. Therefore, the exact determination of the clinical phenotype is of great importance for the individual prognosis, the planning of therapies and participation in clinical trials.