The L1 syndrome may manifest itself as one of several phenotypes. One of these is the MASA syndrome.
Genetic defect: L1CAM (L1 cell adhesion molecule)
Location: Xq28
Inheritance: X-linked (affected males, carrier females)
Features of the MASA syndrome:
(1) mental retardation (M) – mild to moderate intellectual impairment
(2) aphasia or delayed onset of speech (A)
(3) hypotonia progressing to spastic paraplegia (S), typically with a shuffling gait
(4) adducted thumbs (A)
Additional findings:
(1) variable dilatation of the third ventricle.
where:
• The adducted thumb is due to a developmental defect in the extensor pollicis longis and/or brevis muscles.
