Child and Adolescent Psychiatry Viewpoint: Study Confirms that Siblings of Autistic Children Often Have Autistic Traits

Randall F. White, MD, FRCPC; Andro Giorgadze, MD


April 05, 2006

Autistic Social Impairment in the Siblings of Children With Pervasive Developmental Disorders

Constantino JN, Lajonchere C, Lutz M, et al.
Am J Psychiatry. 2006;163:294-296

Using the Social Responsiveness Scale, the investigators assessed autistic characteristics of 100 boys with autistic disorder, Asperger's disorder, or pervasive developmental disorder (PDD) not otherwise specified. All subjects were 4 to 18 years of age and had a brother without any PDD who underwent the same assessment. Some of the subjects came from families with more than 1 PDD-diagnosed child. About half as many boys with non-PDD psychiatric diagnoses, each with a brother without mental illness, were drawn from the same clinic to serve as control subjects. The Social Responsiveness Scale relies on parent and teacher reports and provides a numerical score; higher scores indicate more autistic impairment.

The brothers of boys with any PDD had higher scores than the brothers of children with other psychiatric diagnoses. In addition, the brothers of children from families with multiple PDD diagnoses had the highest scores (P < .000001 compared with controls).

Nonquantitative observations have suggested that siblings of autistic children often have autistic traits. This study provides firmer evidence for the concept of an autistic spectrum in families. The familial nature of autistic disorder and Asperger's disorder is established, which is sometimes due to predisposing genetic disorders such as fragile X syndrome[1] and tuberous sclerosis.[2] Those diseases, however, account for a minority of PDDs and therefore probably account for few occurrences of autistic traits. In any event, this study had insufficient subjects and scope to establish pedigrees and confirm genetic transmission; furthermore, it included no girls.

The heritability of autism resembles that of schizophrenia, in which schizotypal personality disorder and specific endophenotypes exist in the relatives of probands.[3] Only rarely, such as in 22q deletion syndrome,[3] is schizophrenia due to an identifiable genetic defect. Quantifying subsyndromal phenotypes and endophenotypes is an important approach to elucidating the genetics of these complex disorders.



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