L1 syndrome is a mild to severe congenital disorder with hydrocephalus of varying degrees of severity, intellectual disability, spasticity of the legs, and adducted thumbs. It includes several conditions, some more severe than others: X-linked hydrocephalus with stenosis of the aqueduct of Sylvius (HSAS) – the most severe of all; MASA syndrome (intellectual disability, aphasia (delayed speech), spastic paraplegia (shuffling gait), adducted thumbs); SPG1 (X-linked complicated hereditary spastic paraplegia type 1) X-linked complicated corpus callosum agenesis. It is inherited in an X-linked manner; therefore, it only affects males. It is caused by alterations (mutations) in L1CAM gene. The diagnosis is made in males who have the clinical and neurologic findings and a family history consistent with X-linked inheritance and is confirmed by a genetic test showing the L1CAM gene mutation. The treatment involves doing a surgery for the hydrocephalus.
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