Monozygotic twins of different sex.

A pair of monozygotic twins of different apparent sex are described.We consider the discordance as to sex to be due to the loss of a Y chromosome at one of the cell divisions preceding the formation of the germinal discs derived from a single zygote.Case Reports Case 1. J. P. (female) presented with amenorrhoea at the age of I5 and was diagnosed as a case of Turner's syndrome.She was included in a sex chromatin survey of endocrinological cases, and noted to be a twin at this investigation.On examination her height was 4 ft.7 in.(I40 cm.); span 4 ft.9 in.(I46 cm.); height to symphysis 2 ft.3j in.(70 cm.); and weight 6 st.6 lb.(29 kg.).There was no webbing, no breast development, and no axillary hair, but there was scanty pubic hair.There were no other abnormalities apart from shortness and immaturity.She was treated by cyclic medication with oestrogen and progesterone (stilboestrol 3 mg./24hr. for 20 days; ethisterone i8o mg./24 hr. for io days.Menstruation became established and the breasts developed.During the next five years she grew 4.5 in.(iI cm.) and put on 28 lb.(I2-7 kg.).