Verbal skills in relatives of autistic females.

First-degree relatives of 26 autistic females and 26 Down's syndrome females were tested on a battery of verbal tasks designed to detect subtle anomalies. No differences were found when comparing parents of the two groups, but there was a significant difference between siblings. This result was accounted for by a lower performance of the brothers of autistic subjects. The verbal scores of the relatives, either parents or siblings, were not related to the IQ of the proband. Findings are discussed in relation to the hypothesis of genetic and/or environmental factors in autism.