X-linked hydrocephalus: a novel missense mutation in the L1CAM gene.

X-linked hydrocephalus is associated with mutations in the L1 neuronal cell adhesion molecule gene. L1 protein plays a key role in neurite outgrowth, axonal guidance, and pathfinding during the development of the nervous system. A male is described with X-linked hydrocephalus who had multiple small gyri, hypoplasia of the white matter, agenesis of the corpus callosum, and lack of cleavage of the thalami. Scanning the L1 neuronal cell adhesion molecule gene in Xq28 revealed a novel missense mutation: transition of a guanine to cytosine at position 1,243, which led to conversion of alanine to proline at position 415 in the Ig 4 domain of the L1 protein. It is likely that the X-linked hydrocephalus and cerebral dysgenesis are a result of the abnormal structure and function of the mutant L1 protein.

Occurrence of deletion of a COL2A1 allele as the mutation in Stickler syndrome shows that a collagen type II dosage effect underlies this syndrome.

We describe a novel type of mutation in the COL2A1 gene in a family with Stickler syndrome, namely a deletion of an entire COL2A1 allele. Until now, almost all COL2A1 mutations found in this syndrome are nucleotide substitutions, small deletions, or insertions, resulting in premature translation termination. Since the phenotype in this family is not different from cases with a truncated alpha-chain, our finding supports the suggestion that a dosage effect is underlying Stickler syndrome. Moreover, in mutation screening protocols for COL2A1 one should be aware of the possibility of large deletions, which are not detected by generally used PCR-based methods.