Definition of Mental retardation and clasped thumbs

Reviewed on 3/29/2021

Mental retardation and clasped thumbs: A syndrome with the following characteristic features:
(1) Neurological: Mental retardation and aphasia (lack of speech);
(2) Limbs: Clasped (adducted) thumbs, absent extensor pollicis longus and/or brevis muscles to the thumb, shuffling gait, and leg spasticity;
(3) Skeleton: Lumbar lordosis (swayback);
(4) Growth: Small body size.

The syndrome is inherited as an X-linked recessive trait and so affects almost exclusively boys. Alternative names for the syndrome include MASA syndrome (MASA stands for mental retardation, aphasia, shuffling gait, and adducted thumbs), adducted thumb with mental retardation, congenital clasped thumb with mental retardation, and the Gareis-Mason syndrome.

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