X-linked mental retardation, macro-orchidism, and the Xq27 fragile site.

Twenty-three families with X-linked mental retardation were examined for the presence of a fragil site on the long arm of the X chromosome (Xq27 fra). Specific culture media were necessary to demonstrate this site. In only seven of the families was the Xq fragile site observed; in these, all of the affected males had both the fragile X and macro-orchidism. Macro-orchidism was not observed in the remaining 16 families. In the families with Xq27 fra segregating the fraes. This correlated with the age of the carrier. The 25 affected males with macro-orchidism and Xq27 fra had some minor clinical features in common: there was an increase in birth weight, high forehead, prognathism, pale irides, big ears, and an increased head circumference in infancy and childhood which did not persist into adult life. The majority of the affected individuals were moderately retarded.