Are there regions with a particularly high incidence of ALS?

In Germany and Europe, a similar incidence rate can be assumed. Nevertheless, regional differences are possible, and the causes of these differences have not yet been clarified. Information on the extent of these regional differences is expected to come from “ALS registries,” which are currently being established in the Swabia region and other federal states. There have been repeated reports of small towns where several people have developed ALS at the same time. This also applies to companies where coworkers have developed ALS within a short period of time.

For decades, these patterns have given rise to hypotheses about environmental factors that might cause regional or collective clusters of ALS. These external factors have not yet been identified. It also remains unclear whether the reports actually reflect regional clusters or are rather statistical phenomena. This means that there is no statistical “uniform distribution” in the occurrence of diseases.

This phenomenon can be observed in dice games—for example, a particular number may come up especially frequently or even consecutively over several rolls, even though that number appears only once on the die. This explains why ALS is diagnosed multiple times in a row within the same group. Unlike statistical effects (an apparent clustering of ALS cases), it is likely that genetic factors contribute to a genuine clustering of ALS in certain regions. Thus, in regions with low genetic “mixing” (e.g., due to the isolation of populations on islands), there may be an increased genetic risk for ALS.

The island of Guam is a rare example of a genuine regional cluster of ALS. From the 1940s to the 1960s, a complex neurological disorder with similarities to ALS was the leading cause of death in some villages on the island of Guam. The condition was a combination of ALS, Parkinson’s syndrome, and dementia. It was termed the Guam ALS-Parkinson’s-Dementia Complex. The cause of the regional cluster was originally suspected to be certain toxins consumed by the local population through their diet (products of cycads).

In his book *The Island of the Cycads*, New York-based neurologist and author Oliver Sacks reported on the high incidence of ALS on Guam and the hypotheses surrounding it. Oliver Sacks gained widespread fame through his book *Awakenings* (which was adapted into a highly successful film). The toxin hypothesis regarding the high incidence of ALS on Guam has not yet been proven.

An alternative hypothesis is that genetic factors have accumulated within the isolated population on Guam. In fact, the prevalence of the ALS-Parkinson’s-dementia complex on Guam has decreased dramatically. This effect could be explained both by genetic mixing (increased immigration to Guam from populations with different genetic backgrounds) and by changes in dietary habits (reduction in toxin exposure). The high prevalence of ALS-like disease on Guam is a medical-historical phenomenon whose cause has not yet been fully elucidated. No comparable regional clusters are known in Germany or Europe.