The molecular basis of intellectual disability: novel genes with naturally occurring mutations causing altered gene expression in the brain.

This review on the genes implicated in mental retardation, and its X-chromosome linked forms, we presented at the symposium 'The Regulation of Gene Expression in the Brain' (January 23-26, 2003, Heron Island Australia). The main purpose of the review was to highlight the current knowledge of the spectrum of the genes causing mental retardation, provide an insight in to their function(s), where known, and to speculate about the evolutionary processes which shaped such an unexpected concentration of these genes on the human sex chromosome X. Such genes with naturally occurring mutations provide an invaluable opportunity for identifying the pathways essential for the normal function of the brain. Once identified, cellular and animal models can then be used for experimentation