MASA syndrome is a rare neurological disorder with an X-linked recessive mode of inheritance. It is characterized by mental retardation, adducted thumbs, shuffling gait, and aphasia. Other symptoms and physical findings include abnormal widening of cavities within the brain and accumulation of excessive cerebrospinal fluid in the hydrocephalus, mild short stature, abnormally increased inward curvature of the lower spine (exaggerated lumbar lordosis), and other skeletal abnormalities. Brain imaging provides evidence of dilated cerebral ventricles, hypoplasia or agenesis of the corticospinal tract, stenosis of the aqueduct of Sylvius, and agenesis of the corpus callosum.