Mutations in the gene encoding the neuronal cell adhesion molecule L1 are responsible for several syndromes with clinical overlap, including X-linked hydrocephalus (XLH, HSAS), MASA (mental retardation, aphasias, shuffling gait, adducted thumbs) syndrome, complicated X-linked spastic paraplegia (SP 1), X-linked mental retardation-clasped thumb (MR-CT) syndrome, and some forms of X-linked agenesis of the corpus callosum (ACC).
The L1CAM gene, which is located in Xq28 and codes for a neuronal cell adhesion molecule, is involved in three distinct conditions: HSAS (hydrocephalus-stenosis of the aqueduct of Sylvius), MASA (mental retardation, aphasia, shuffling gait, adductus thumbs), and SPG1 (spastic paraplegia).