To evaluate the contribution of polymorphisms in the vitamin D receptor (VDR) gene to ethnic variations in bone mass in mother and children from different ethnic origins.
VDR genotypes and bone mass in 43 African-American and white women, mean age 38.2 years, and 41 of their children were studied. All children had a whole body bone mass measurement at age 9, and 39 had follow up measurements at age 11, while all the mothers had a single measurement. DNA was extracted from peripheral blood samples, subjected to polymerase chain reactions using primers specific for the VDR gene, and the Bsm1 restriction fragment length polymorphism defined.
There was a significant ethnic difference in the VDR genotype frequencies among the adults and the children. No African-American subjects had the genotype "BB". In contrast, there was a 25% frequency of the "BB" genotype in the white adults and 24% in the white children. After pooling the ethnic groups, the mean bone mass in the "bb" genotype was significantly higher than in the "BB" genotype among the mothers, but this was not found in the children at baseline. However, by age 11, those with the "Bb" or "bb" genotypes had a larger gain in bone mass than those with "BB".
These data support the suggestion that the ethnic difference in VDR genotype frequencies, together with the association between the genotypes and bone mass, may help to explain the well known ethnic differences in bone mass. Further, our observations suggest that VDR polymorphism may have an effect on bone mass during puberty as peak bone mass is accumulated.