Familial autism and the fragile-X chromosome.

This report presents two male siblings in whom the diagnosis of infantile autism was found in association with a fragile site on the X chromosome. In addition to their marked autistic characteristics, formal examinations indicated that both boys were severely mentally retarded and had several physical features commonly observed in association with the fragile-X syndrome. The mother of these two siblings also gave birth to identical twin boys, who were developmentally delayed and showed several autistic features prior to their untimely death in a house fire. The possible role of the fragile-X chromosome as an etiological factor in families where there is a clustering of autism and related developmental disturbances is discussed.