Concordance and discordance of congenital hydrocephalus in 107 twin pairs in Japan

During the period from 1969 to 1985, 107 pairs of twins, of which at least one in each pair had congenital hydrocephalus, were ascertained in Japan. The rate of concordance for hydrocephalus among these twins was 15%, with a slightly higher rate in like-sex male twins (28%) than in like-sex female twins (14%). The rates were 21% in like-sex and 0% in unlike-sex pairs. Two twin pairs had one anencephalic twin and one hydrocephalic twin.