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Mike Mitka

JAMA. 2009;301(21):2202.

	Since this article does not have an abstract, we have provided the first 150 words of the full text and any section headings.

A 5-year international collaboration of 70 scientists has led to the identification of 9 genes that, when mutated, are associated with X-linked mental retardation (XLMR) [Tarpey PS et al. Nature Genet. 2009;41(5):535-543].

The researchers sequenced 720 of the about 800 known genes on the X chromosome in 208 families affected by the condition. The 9 new genes can now be added to the approximately 80 previously identified genes involved in this group of intellectual disabilities, allowing for more comprehensive genetic counseling. The researchers cautioned, however, that most of the mutated genes responsible for XLMR have not been identified.

An interesting added discovery by the researchers is that for some (about 1%-2%) of the X chromosome genes, when they do not function, no ill effects appear to occur in the affected person. The researchers said this finding should warn geneticists to be cautious when drawing a direct link . . . [Full Text of this Article]

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