Probable inverted tandem duplication of Xp in a 46,Xp+Y boy

A mentally retarded 16-month-old boy with subnormal stature, strabismus, anteverted nares and deformed ears was found to have ade novo structural rearrangement of the X chromosome (46,Xp+Y). The banding patterns of the abnormal X chromosome were interpreted to be an inverted tandem duplication of the segment Xp22.1→Xp22.3. Several other possibilities were considered but thought less likely. DNA replication studies with BrdU incorporation revealed the replication pattern of the duplicated segment to be similar to the equivalent portion of the X chromosome.