Congenital hydrocephalus internus and aqueduct stenosis: aetiology and implications for genetic counselling

Genetic counselling in families with congenital hydrocephalus internus (CHI ) in combination with aqueduct stenosis (AS) is often difficult due to an u ncertain aetiology. We present a series of 35 patients with CHI and AS focu sing on the aetiology and presumed recurrence risk for siblings. In 13 pati ents (37.1%) a genetic aetiology was identified with an increased recurrenc e risk for siblings. The relative frequency of patients with X-linked hydro cephalus in our sample was in accordance with the literature (2/35), but wa s more frequent in other diseases with Mendelian inheritance. Conclusion In addition to the well-known X-linked and autosomal recessive f orms of aqueduct stenosis with hydrocephalus, this malformation can occur i n other diseases with Mendelian inheritance. This finding is of considerabl e importance fur genetic counselling and prognosis.