L1 syndrome is an inherited, X-linked disorder occurring in males that primarily affects the nervous system. The disease is mainly characterized by hydrocephalus (increased fluid in the center of the brain), spasticity of the lower limbs (muscle stiffness), adducted thumbs (clasped towards the palm), aphasia (difficulty with speaking), seizures, and agenesis of the corpus callosum (underdeveloped or absent connecting tissue between the left and right hemispheres of the brain). Affected individuals have intellectual disability in the mild to moderate range. L1 syndrome is caused by abnormalities (mutations) in the L1CAM gene, which affects about 1 in 30,000 males.
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