Genetic aspects of "uncomplicated" hydrocephalus and its relationship to neural tube defect.

Congenital hydrocephalus is a relatively uncommon abnormality in population malformation surveys accounting for between four and ten out of every 10,000 births. In 30%, it is caused by aqueduct stenosis. The majority of cases have a multifactorial aetiology, the genetic component, which is polygenic, rendering the developing foetus susceptible to largely unidentified environmental factors in early development. Some cases are caused by single gene defects. Family studies suggest that the risk to siblings of a child with uncomplicated congenital hydrocephalus, where the anatomical site is not specified, is about 1 in 50 (1 in 40 for males, 1 in 80 for females). With aqueduct stenosis, the risk to brothers of affected boys is 1 in 22, to sisters only 1 in 50. The risks to siblings of sisters is less. Probably less than 2% of uncomplicated hydrocephalus has an X-linked basis and such an aetiology should be suspected if the special clinical features are present, there is more than one male sibling affected, or there are affected male relatives on the mother's side. Dandy-Walker's syndrome may be recessively inherited and there are some other, but very rare, monogenic causes for hydrocephalus. There is not obvious additional risk for neural tube defect. Non-directive genetic counselling should be given either at the genetic clinic or at a specially arranged clinic appointment and should include not only the risk to the family members, but also the options for avoiding recurrences, and any prenatal diagnostic tests available, such as high precision ultrasonography and a serum alphafetoprotein estimation at about sixteen weeks gestation.(ABSTRACT TRUNCATED AT 250 WORDS)