The purpose of this study is to test the hypothesis that major affective and/or anxiety disorders are increased among relatives of autistic probands compared with controls. Among 36 families with an autistic child, 23 (64%) have a first degree relative diagnosed with major depressive disorder and 14 (39%) have a first degree relative diagnosed with social phobia. These rates are significantly greater than the 19% and 5%, respectively, found among 21 families with a child having a genetic condition, tuberous sclerosis complex, or a seizure disorder but no autism. The frequency of major depression among the 96 first degree relatives of autistic probands is 37.5% compared with 11.1% found among 45 relatives of control probands. The frequency of social phobia, 20.2%, is approximately 10 times more common than that found among the relatives of the control probands (2.4%). Elevated rates of both major depression and social phobia are found among parents and siblings in the families with an autistic child. Furthermore, 64% of parents affected with a major depression had the onset of the first depressive episode prior to the birth of the autistic child and all parents with social phobia had the onset of condition prior to the birth of the autistic child.
Family patterns differ depending on the intellectual level of the autistic child; specifically, social phobia is significantly greater among the first degree relatives of nonretarded autistic probands than among relatives of individuals with autism and comorbid mental retardation. Whether this familial association of autism, major mood disorders, and social phobia reflects shared genetic underpinnings requires further research. © 1995 Wiley-Liss, Inc.