Clinicopathological conference: a newborn monozygotic twin with abnormal facial appearance and respiratory insufficiency.

The second of twins males expired of respiratory insufficiency shortly after birth. Unusual facial appearance included prominent forehead, flat nasal bridge, widely separated inner canthi, downward slanting eyes with narrow palpebral fissures, epicanthic folds, small mouth and micrognathia, and apparently low-set ears; there was also cryptorchidism bilaterally and a simian crease bilaterally. The pregnancy of the 19-year-old black woman was not unusual, but polyhydramnios accompanied the delivery of this twin. The twin placentae were diamniotic and monochorionic, one being slightly immature with a two-vessel cord. We interpreted the karyotype as 46,XY,del(10) (p11-15): The brother and parents were normal. The dysmorphic features of this and three previously reported cases of 10p- do not permit definition of a syndrome. These are apparently the first monozygous twins presenting discordance of chromosomal structure; previously reported chromosomal discordance in monozygous twins involved numerical abnormality. Considering that the mechanism monozygous twinning is not understood, we note that the occurrence of both twinning and a structural aberration in one of the twins suggests the possibility of a common cause.