[From gene to disease; X-linked hydrocephalus and LiCAM].

X-linked hydrocephalus (hydrocephalus due to congenital stenosis of aqueduct of Sylvius; MIM number 307000) has a variable clinical expression. About 5% of cases of non-syndromal hydrocephalus are affected by this condition. The severe clinical phenotype is characterized by hydrocephalus and adducted thumbs in a newborn boy, the milder phenotype by mental retardation and spastic paraplegia. Female carriers may show mild features. Mutations in the LiCAM gene have been demonstrated to cause the condition. The gene is located at Xq28 and encodes for a cell surface glycoprotein that consists of an extracellular part with 6 immunoglobulin and 5 fibronectin type III-like domains, a single pass transmembrane domain and a short cytoplasmic domain. Mutations are documented in about 75% of classical cases. Reliable prenatal diagnosis is possible when a mutation has been documented.