Genotyping of PCR-based polymorphisms and linkage-disequilibrium analysis at the NF1 locus

Six polymorphisms across the NF1 gene have been adapted for genotyping through application of PCR-based assays. Three exon-based polymorphisms--at positions 702, 2034, and 10647 in the NF1 cDNA--were genotyped by mutagenically separated PCR (MS-PCR). A fourth polymorphism, DV1.9, is an L1 insertion element in intron 30, and the other two polymorphisms, GXAlu and EVI-20, are short tandem repeats in intron 27b. All the polymorphisms were evaluated in a cohort of 110 CEPH individuals who previously had been analyzed by use of eight RFLPs at the NF1 locus. Pairwise linkage-disequilibrium analyses with the six PCR-based polymorphisms and their flanking markers demonstrated disequilibrium between all tested loci. Genotypes of the four diallelic polymorphisms (702, 2034, 10647, and DV1.9) were also evaluated in cohorts from the CEPH, African, and Japanese populations. The CEPH and Japanese cohorts showed similar heterozygosities and linkage-disequilibrium coefficients. The African cohort showed a higher degree of heterozygosity and lower linkage-disequilibrium values, compared with the CEPH and Japanese cohorts.