ALS is classified as a rare disease, designated by the FDA as an "orphan" disease (affecting fewer than 200,000 people in the United States), but is the most common motor neuron disease.
Reports have been made of several "clusters" including three American football players from the San Francisco 49ers, more than 50 association football players in Italy,[REF] three association football-playing friends in the south of England,[REF] and conjugal (husband and wife) cases in the south of France [REF].