Congenital hydrocephalus: nosology and guidelines for clinical approach and genetic counselling

Congenital hydrocephalus is a serious condition that can arise from multiple causes. It comprises a diverse group of conditions which result in impaired circulation and absorption of cerebrospinal fluid. Congenital malformations of the central nervous system, infections, haemorrhage, trauma, teratogens and, occasionally, tumours can all give rise to hydrocephalus. In this paper we focus on the genetic aspects of hydrocephalus, excluding neural tube defects. The incidence is 0.4-0.8 per 1000 liveborns and stillbirths. X-linked hydrocephalus comprises approximately 5% of all cases. This condition is caused by mutations in the gene at Xq28 encoding for L1, a neural cell adhesion molecule. Carrier detection and prenatal diagnosis can be offered to affected families by means of chorionic villus biopsy and linkage analysis or L1 mutation analysis. In general, recurrence risk for congenital hydrocephalus excluding X-linked hydrocephalus, is low; empiric risk figures found in various studies range from <1% to 4%. Unfortunately, prenatal diagnosis based on an early ultrasound scan is not always reliable as ventriculomegaly usually starts after 20 weeks of gestation. We stress the importance of additional clinical investigations. Prognosis in the prenatally diagnosed patients depends on additional malformations but in general, is not very good.

Congenital hydrocephalus may be non-syndromic and syndromic. Prognosis depends primarily on the underlying cause and/or associated malformations, which have to be delineated on the basis of clinical, cytogenetic and molecular analysis.