The greeting behavior of fragile X males.

Mentally retarded males with a fragile site on the X chromosome (Xq27) were observed to exhibit a highly idiosyncratic but well-coordinated, stereotypic form of gaze avoidance during greeting ceremonies that involved the whole upper body. A comparison group of persons with other etiologically defined syndromes of mental retardation did not. Results suggest that the aberrant greeting behavior may be uniquely associated with one syndrome of mental retardation with a defined genetic etiology. The behavior pattern does not appear until middle childhood, however, and its developmental induction remains to be explained.