Fragile X syndrome. Improving understanding and diagnosis

Fragile X syndrome (Martin-Bell syndrome)1is the most common cause (one in 1500 males) of mental retardation from a single gene defect. The discovery of the fragile X mental retardation—1 (FMR1) gene and its mutation (CGG triplet repeat enlargement) in 19911-4has prompted intensive molecular studies of both the gene function and the mechanism by which the triplet repeat further expands from generation to generation.5-8In this issue, the article by Warren and Nelson9summarizes the rapid increase in our molecular knowledge of the disease. In another article, Taylor et al10have retrospectively investigated female carriers of fragile X mutations for correlation of mental retardation syndrome with DNA-based methods of measuring the triplet repeat mutation. There is a great deal to be learned from both articles. See also pp 507 and 536. The physician is at a disadvantage in making a clinical diagnosis of fragile