Advances in X-linked mental retardation

PURPOSE OF REVIEW: Mutations in genes on the X chromosome rival chromosome aberrations as a cause of mental retardation. Progress in the clinical and molecular delineation of X-linked mental retardation has outpaced progress in understanding autosomal mental retardation. This is a result in large part of the identification of large families in which mental retardation has segregated in an X-linked pattern and the greater ease with which molecular technologies can be applied to hemizygosity in males. RECENT FINDINGS: About one-third of the estimated 165 genes associated with syndromal mutations of genes on the X chromosome and one-fourth of the estimated 100 genes associated with nonsyndromal mutations of genes on the X chromosome have been identified. In a number of instances, the same gene is responsible for syndromal and nonsyndromal mutations of genes on the X chromosome. The molecular delineation of mutations of genes on the X chromosome has allowed certain conditions to be lumped together on the basis of allelism and has caused others that appear clinical similar to remain separate. SUMMARY: The clinical and molecular advances have allowed X-linked mental retardation to be more clearly delineated, have provided the means of confirmatory laboratory testing, and have ushered in an era of carrier testing, prenatal diagnosis, and prevention strategies.