PERSPECTIVES AND MOLECULAR DIAGNOSIS OF THE FRAGILE-X SYNDROME

The fragile X syndrome is the most common mendelianly inherited form o f mental retardation. The underlying mutation is usually a triplet rep eat (CGG) that is variable in length and undergoes a tremendous length amplification in affected individuals. The mutation leads to absence expression of a gene, which apparently functions as an RNA binding pro tein. Molecular diagnostic testing for the mutation is conducted using direct genomic Southern blot analysis and polymerase chain reaction. Because the mutation is so common and a single type of mutation accoun ts for most individuals with the disease, widespread genetic screening can be considered.