Pichechero notes that PANDAS has not been validated as a disease classification, for several reasons. Its proposed age of onset and clinical features reflect a particular group of patients chosen for research studies, with no systematic studies of the possible relationship of GAS to other neurologic symptoms. There is controversy over whether its symptom of choreiform movements is distinct from the similar movements of Sydenham's. It is not known whether the pattern of abrupt onset is specific to PANDAS. Finally, there is controversy over whether there is a temporal relationship between GAS infections and PANDAS symptoms.