Although the precise etiological nature of autism—the most common development disorder—remains elusive, two main biological factors have been suggested. One is related to a possible neurochemical dysfunction at the level of the serotonergic system; the other underlines the presence of neuroanatomical abnormalities in different areas, in particular, in the cerebellum.

The authors propose a unifying hypothesis linking serotonin (5-hydroxytryptamine, or 5-HT) to the cerebellum on the basis of the observation of a specific 5-HT receptor subtype, 5-HT5A, in this area. The 5-HT5A receptors may be involved in the pathophysiology of autism, and perhaps, in autism-related disorders, since they are mainly expressed in Purkinje's cells. Future studies with specific drugs that interact with 5-HT5A receptors should permit the testing of this hypothesis through the evaluation of the receptors themselves in autopsied brain samples or in vivo by positron emission tomography. Theoretically, such compounds might prove effective in the treatment of autism.