Detection of full fragile X mutation.

In fragile X syndrome, the most common inherited cause of mental deficiency, the underlying mutation is a large increase in the number of CGG repeats in a gene on chromosome X. We have developed a polymerase chain reaction (PCR) method to amplify across the full mutation in affected individuals. In this report, a fragile X family including a positive prenatally diagnosed fetus was analysed by PCR, and the results are consistent with direct genomic Southern blot analysis. Genetic screening of at-risk populations for fragile X can now be achieved by PCR rapidly, inexpensively, and on small samples.