Family study of congenital hydrocephalus.

This study concerned 74 patients with uncomplicated congenital hydrocephalus who were born in Northern Ireland between 1974 and 1977. Three of their 159 sibs (1.89 per cent) were also themselves hydrocephalic, which represents a recurrence risk of 26 times the population incidence. There was a smaller but significant increase of congenital hydrocephalus among first-cousins; three of 846 (0.35 per cent) first-cousins were affected, five times the population frequency. The occurrence of neural-tube defects among sibs and cousins was similar to that for the general population. For the purpose of genetic counselling, this study indicates that once X-linked inheritance has been excluded in uncomplicated congenital hydrocephalus, the over-all empirical risk of recurrence is approximately one in 50; or one in 40 after an affected male and one in 80 after a female index patient.