A new X-linked mental retardation syndrome.

We have studied a three-generation family with 11 moderately to severely retarded males and three mildly retarded females (presumably manifesting carriers). The patients have a phenotype different from that of all other previously described types of X-linked MR (XLMR). These include short stature, macrocephaly, "coarse" facial appearance including prominent forehead and supraorbital ridges, hypertelorism, broad nasal tip with anteverted nostrils, and thick lips. All postpubertal males had macroorchidism (volume greater than 25 ml). Chromosomes were normal including fragile X analysis. X-ray findings of skull, spine, and hands were normal. The intellectually normal relatives do not resemble their affected relatives except for increased head size and testicular size. These findings suggest a new variant of XLMR different from fragile X-linked MR, the Coffin-Lowry syndrome, and other XLMR conditions.