MOLECULAR-BIOLOGY OF FRAGILE-X SYNDROME - APPLICATIONS TO GENETIC-COUNSELING AND MOLECULAR DIAGNOSIS

Fragile X syndrome is the most common cause of inherited mental retard ation. Since the identification of the mutation, a Cytosine-Guanine-Gu anine repeat in the Fragile X Mental Retardation (FMR1) gene, the gene tic counselling and the diagnosis of the disease have been dramaticall y improved. The nature of the mutation and its size must be integrated in the calculation of the risk of transmission of mental retardation and in the genetic counselling in the family. Out of 245 patients affe cted with mental retardation referred to our laboratory, we found 37 ( 15 %) fragile X patients, allowing to screen for the mutation in the f amily and to propose prenatal diagnosis in carrier females.