MASA syndrome, also called CRASH syndrome and Gareis-Mason syndrome, is a rare X-linked recessive neurological disorder.
The acronym "MASA" describes the four major symptoms - Mental retardation, Aphasia, Shuffling gait, and Adductedthumbs. A more suitable name for this syndrome is "L1 syndrome". The disorder has been associated with mutations in the L1CAM gene. This syndrome has severe symptoms in males, while females are carriers because only one X-chromosome is affected. Affected males can't reproduce so their X-Chromosome isn't inherited. (The term "CRASH", for "corpus callosumhypoplasia, retardation, adductedthumbs, spastic paraplegia, and hydrocephalus" has also been used to describe L1CAM-related disorders.) A prenatal diagnostic is possible and very reliable when mother is carrier of the syndrome. First, it's necessary to determine the fetus' sex and then study X-chromosomes. In both cases, the probability to transfer the X-chromosome affected to the descendants is 50%. Male descendants who inherit the affected chromosome will express the symptoms of the syndrome, but females who do will be carriers. 
^Winter RM, D. K.; Davies, K. E.; Bell, M. V.; Huson, S. M.; Patterson, M. N. (July 1989). "MASA syndrome: further clinical delineation and chromosomal localisation". Human Genetics82 (4): 367–370. doi:10.1007/bf00273999. PMID2737668.edit
^Fransen E, Lemmon V, Van Camp G, Vits L, Coucke P, Willems PJ (1995). "CRASH syndrome: clinical spectrum of corpus callosum hypoplasia, retardation, adducted thumbs, spastic paraparesis and hydrocephalus due to mutations in one single gene, L1". European Journal of Human Genetics3 (5): 273–84. PMID8556302.