100 to 200 servings of any sweetener is a lot!
Those people are phenylketonuronics; they are born with a metabolic disorder that prevents their bodies from completely metabolizing phenylalanine (a component of Aspartame). Metabolites of phenylalanine build up and cause damage to the nervous system. These people must eat a very restrictive diet; if the disease is not caught and treatment begun early (i.e. in babyhood), mental retardation will result. Very often, by the time the disease is diagnosed, brain damage has already resulted.