Fragile X syndrome. Molecular and clinical insights and treatment issues.

The fragile X syndrome is the most common inherited cause of mental retardation that is known. The prevalence of mental retardation from this syndrome ranges from 1 in 1,250 to 1 in 4,000 in the general population, although the prevalence of female carriers has been reported to be as high as 1 in 259. The discovery of the FMR1 gene mutation in 1991 has simplified diagnosis, enhanced our understanding of the spectrum of involvement in the fragile X syndrome, and stimulated research regarding the normal function of the FMR1 protein in brain development. Advances have also occurred in the treatment of the fragile X syndrome, and psychopharmacologic and educational interventions are reviewed here.