Clasped thumbs and mental retardation: A syndrome with the following characteristic features: (1) neurologically: mental retardation and aphasia (lack of speech); (2) limbs: adducted (clasped) thumbs, absent extensor pollicis longus and/or brevis muscles to the thumb, shuffling gait, and leg spasticity; (3) growth: small body size; (4) skeleton: lumbar lordosis (sway back). The syndrome is inherited as an X-linked trait and so affects mainly boys. Alternative names 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.