Cytogenetic survey for autistic fragile X carriers in a mental retardation center.

A cytogenetic survey of 67 individuals previously identified as having mental retardation and autistic behaviors revealed 1 person (1.5%) with the fragile X chromosome (fra[X]) and 3 (4.5%) with autosome abnormalities. This low prevalence of fra(X) indicates that most persons with fra(X) in this mental retardation center did not have autistic behaviors severe enough to be identified as a secondary psychiatric diagnosis. The presence of other chromosomal abnormalities is consistent with the known causal heterogeneity of autism in mental retardation populations.