THE IDENTIFICATION OF A (CGG)(6)AGG INSERTION WITHIN THE CGG REPEAT OF THE FMR1 GENE IN ASIANS

We have evaluated the structure of the CGG repeat within the FMR1 gene of an Asian population and found the most common size of the repeat t o be 29 and 30 with a minor population of 36 repeats. We have isolated and sequenced DNA containing the 36 repeats and found the basis seque nce to be (CGG)(9)AGG(CGG)(9)AGG-(CGG)(6)AGG(CGG)(9); with a (CGG)(6)) AGG insertion, designated as 9A9A6A9. Of 144 Asian chromosomes, 11 (8% ) had sequences with this insertion. Six different variations of the b asic sequence were observed in the population: 9A9A6A2A9, 9A9A6A11, 9A 9A16, 9A9A15, 8A9A6A6A9, and 11A6A6A9. All but one of the chromosomes with the insertion had the haplotype of DXS548/FRAXAC1: 194/D suggesti ng that the sequences with the 6A insertion arose from a single ancest ral allele. We have not observed the insertion in the FMR1 gene of Cau casians or Native Americans. The (CGG)(6)AGG insertion may be unique t o Asians.