NONRADIOACTIVE DNA DIAGNOSIS FOR THE FRAGILE-X SYNDROME IN MENTALLY-RETARDED JAPANESE MALES

A rapid screening test was developed to detect CGG repeat expansion of the FMR-1 gene causing the fragile X syndrome by a non-radioisotope P CR technique. A biotin-labeled primer was initially used and the bioti n-labeled PCR product was detected by means of chemiluminescence. The normal PCR product of around 300 bp was not created in the abnormal FM R-1 gene sample with this method. Four positive samples were found amo ng those from 226 mentally retarded males, but the CGG repeat expansio n was shown on Southern blot analysis in only one sample. To eliminate false-positive samples, a hybridization method involving a biotin-lab eled (CGG)(5) oligonucleotide was developed for the PCR product and th e CGG repeat expansion could be detected. Finally, 256 mentally retard ed males in Japan were examined and only 2 abnormal samples were detec ted. The prevalence of this abnormality was less than 1%, which is rel atively lower than those reported previously.