Introduction

Almost 30 years ago Hanson and Gottesman (1976) published a review article entitled “The genetics, if any, of infantile autism and childhood schizophrenia.” As the title suggests, the two authors found little evidence of a genetic role in the etiology of autism. “No strong evidence exists,” they wrote, “implicating genetics in the development of childhood psychoses that begin before the age of 5.” The viewpoint expressed in this article was not idiosyncratic and was generally held to be true at the time. Currently, the general viewpoint regarding autism has reversed itself completely. Autism today is thought to be one of the most heritable of all psychiatric conditions, more so than bipolar disorder or schizophrenia, and much more so than alcoholism or antisocial behavior. The issue today is not whether autism has a genetic basis but what that basis is, the specific genes involved, and how they act.

Several developments were responsible for this reversal. The most influential was a series of twin studies, the first of which appeared a year after the Hanson and Gottesman review. Folstein and Rutter (1977) attempted “to obtain information on all school-age autistic twin pairs (same sex twins at least one of whom was autistic) in Great Britain.” This attempt was implemented in a variety of ways, including a list of autistic twin pairs collected over the years by the late Dr. M. Carter, a search of the records of all children known to the National Society for Autistic Children, and a request for cases published in the Society's newsletter.