DISTRIBUTION OF FMR-1 AND ASSOCIATED MICROSATELLITE ALLELES IN A NORMAL CHINESE POPULATION

The CGG repeat size distribution of the fragile X mental retardation g ene (FMR-1) was studied in a population of normal Chinese X chromosome s along with that of two proximal microsatellite polymorphic markers: FRAXAC1 and DXS548. The most common CGG repeat allele was 29 (47.2%) w ith 30 being second most common (26%). This distribution was different from that seen in Caucasian controls, where the most common allele wa s 30 repeats. Other differences with Caucasian controls included a sec ondary modal peak at 36 repeats and the absence of peaks at 20 or 23 r epeats. There were only two FRAXAC1 and five DXS548 alleles found in t he Chinese sample. A striking linkage disequilibrium of FMR-1 alleles with FRAXAC1 alleles was observed, in that 90% of the 29 CGG repeat al leles but only 41% of the 30 CGG repeat alleles had the FRAXAC1 152 bp allele (18 AC repeats). This disequilibrium suggests that slippage be tween the closely spaced normal CGG repeat alleles, 29 and 30, and bet ween 152 and 154 FRAXAC1 alleles is very rare. This study lays the gro undwork for an understanding of founder chromosome effects in comparin g Asian and Caucasian populations. (C) 1994 Wiley-Liss, Inc.