Characterization of a novel human X-linked gene RBMX, a candidate for X-linked mental retardation

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We recently discovered a novel gene (which we have called RBMX for RNA-binding protein, X chromosome) on the human X chromosome. Its function is quite unknown, but it is active in all tissues, and it has changed very little in evolution, so we think it must have an important function in human development. Genes with a similar sequence bind to RNA and convert it to its final active form, so RBMX may have a similar role. Other RNA-binding proteins are active in the brain, so we suspect that RBMX may be involved in brain development and learning. The RBMX gene is also interesting because it has a copy called RBMY on the human Y chromosome, which is thought to have a critical (unknown) function in sperm production. Of particular note is our finding that RBMX maps to the long arm of the human X chromosome at Xq26. This is a region that contains several inherited mental retardation syndromes called X linked mental retardation (XLMR) which are carried by females and manifest in males. At least eight XLMR syndromes have been mapped to human Xq26. Several of the syndromes have characteristic skeletal and facial abnormalities, as well as a range of other anomalies.. We will completely characterise the human RBMX gene. As well as giving us fresh clues to its function, this will allow us to make a mouse strain that lacks the gene (knockout) so we can see whether it is critical for life, and if it is involved in brain development and learning. Identification of an XLMR gene coding for an RNA binding protein will shed light on the role of RNA metabolism in the brain, and the effect of disruptions of RNA processing on mental function. We will then screen the RBMX gene in families with XLMR syndromes, to look for RBMX mutations in patients which may cause XLMR. If mutations in RBMX cause one or more XMLR phenotypes, it will be possible to use this knowledge to diagnose the condition and detect carriers.