A missense mutation, p
V132G, in the X-linked spermine synthase gene (SMS) causes Snyder-Robinson syndrome. Snyder-Robinson syndrome (SRS, OMIM 309583) is a rare X-linked syndrome characterized by mental retardation, marfanoid habitus, skeletal defects, osteoporosis, and facial asymmetry. Linkage analysis localized the related gene to Xp21.3-p22.12, and a G-to-A transition at point +5 of intron 4 of the spermine synthase gene, which caused truncation of the SMS protein and loss of enzyme activity, was identified in the original family. Here we describe another family with Snyder-Robinson syndrome in two Mexican brothers and a novel mutation (c.496T>G) in the exon 5 of the SMS gene confirming its involvement in this rare X-linked mental retardation syndrome.