Marker X syndrome in an oriental family with probable transmission by a normal male.

We report an oriental family with sex-linked mental retardation, macroorchidism, and a marker or fragile site on the X chromosome--mar(X)(q28). The three affected males resemble clinically most previously reported affected Caucasians. The marker was present in four female 40-70 years old, including one with normal intelligence. Transmission of the disorder appears to have taken place through a clinically normal male to his grandson.