DXS548/FRAXAC1 haplotypes in fragile X chromosomes in the Brazilian population

In order to investigate the origin of the fragile X mutation in the Brazili an population, we assessed the size of the microsatellite markers DXS548, F RAXAC1 and FRAXAC2 in 72 X chromosomes from unrelated affected males and 64 control chromosomes. We found a significantly different distribution of al leles between fragile X and controls for loci DXS548 and FRAXAC1, but no ap parent linkage disequilibrium was detected for the sequence FRAXAC2, The mo st frequent DXS548/FRAXAC1 haplotypes in affected males were haplotypes 204 /158 bp (2-1) and 196/152 bp (6-4), These findings are in accordance with t he proposed two main mutational pathways for the generation of FMR-1 allele s that predispose to instability and hyperexpansion. (C) 1999 Wiley-Liss, I nc.