Genetic epidemiology of osteoporosis across four microsatellite markers near the VDR gene

Abstract

The large amount of positive genetic association data in a number of bone diseases suggests functional consequences of Vitamin D receptor (VDR) gene polymorphism. In the present study, four microsatellite markers viz., D12S1633, D12S1635, D12S347, and D12S96, that lie in the vicinity of the VDR gene on chromosome 12 were selected to assess the allele distribution pattern and diversity among three groups of individuals - normal, osteopenia and osteoporosis. Genetic association study was performed using allele frequency data. Total genomic DNA was isolated from the whole blood of 226 individuals, after recording their bone mineral density (BMD) using Dual X-ray absorptiometry (DXA). All DNA samples were subjected to multiplex Polymerase Chain Reaction (PCR) - genotyping. Allele frequencies and genetic diversity parameters like - number of alleles, average variance and average heterozygosity across all the four markers among three groups were computed. Effect of population stratification was excluded by investigating population structure. A trend of decreasing genetic diversity across four loci from normal to pre- and post-disease condition has been observed. Lesser recombination rate (θ) indicates linkage between studied microsatellite markers and VDR gene. Statistically significant linkage disequilibrium was detected for the allele - 22 of locus D12S96 with osteoporosis. A positive association of allele - 22 suggests susceptibility to disease whereas predominance of allele - 27 among non - diseased group implicates its association with normal bone health.

Keywords: Genetic diversity; VDR; microsatellites; osteopenia; osteoporosis.

Figure 1

Agarose gel image (2%) of multiplex PCR. Lane - 1, ladder 100 base - pair; Lane - 2 and 3 multiplex PCR products.

Figure 2

Triangle plot showing estimates of membership coefficient (Q) for each individual of sampled groups, analyzed under admixture model, assuming correlated allele frequencies.

Figure 3

Frequency distribution of alleles - 22 and 27 at the microsatellite locus D12S96, among normal, osteopenia and osteoporosis individuals.