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.



• The adducted thumb is due to a developmental defect in the extensor pollicis longis and/or brevis muscles.

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