MASA syndrome (Mental retardation, Aphasia, Spastic paraplegia, Adducted thumbs) is a historical term used to describe a phenotype now considered to be part of the X-linked L1 clinical spectrum (L1 syndrome). MASA is characterized by mild to moderate intellectual deficit, delayed development of speech, hypotonia progressing to spasticity or spastic paraplegia, adducted thumbs, and mild to moderate distension of the cerebral ventricles. The disease is MONDO_0010559 (MASA syndrome). Also known as: Gareis-Mason syndrome, X-linked complicated hereditary spastic paraplegia type 1, X-linked corpus callosum agenesis, X-linked spastic paraplegia 1, hereditary spastic paraplegia 1, intellectual disability-aphasia-shuffling gait-adducted thumbs syndrome, masa syndrome, X-linked recessive, spastic paraplegia, X-linked.