MASA syndrome is a rare hereditary, X-linked recessive disorder that has specific, progressively appearing neurological and clinical signs. MASA is the acronym for the four main characteristics that delineate the syndrome (mental retardation, aphasia, shuffling gait, and adducted thumbs). MASA syndrome is often used interchangeably with CRASH syndrome (also named for its characteristics), which are corpus callosum hypoplasia (underdevelopment), mental retardation, adducted thumbs, spastic paraplegia, and hydrocephalus. Without genetic assay, MASA syndrome is difficult to diagnose in infants and young children because the characteristic symptoms are not apparent until a later age.