Association of Vitamin D Receptor BsmI Gene Polymorphism with BMD Z-Score in Iranian Children and Adolescents (9 - 18 Years Old)

Background: The vitamin D receptor (VDR) gene variants are known as the main risk factor for low bone mass.

Objectives: In this study, the association of vitamin D receptor genetic variants, BsmI (rs1544410) and FokI (rs2228570), with bone mass in Iranian children and adolescents, was evaluated.

Methods: The study population comprised of children and adolescents aged between 9 to 18 years (FokI: 123 boys and 120 girls, BsmI: 108 boys and 110 girls). Vitamin D, calcium, phosphorus, total cholesterol (TC), High-density lipoprotein-cholesterol (HDL-C) and triglyceride (TG) concentrations were assayed. Bone mineral density and body composition parameters were measured by the Hologic system DXA. BMD Z-score ≤ -2 was considered as low bone density for chronologic age. PCR-restriction fragment length polymorphism was done for genotyping of BsmI and FokI polymorphisms. The association between VDR variants and bone mineral density was investigated using logistic regression analysis.

Results: No significant differences in body composition and biochemical parameters were detected among the evaluated VDR genotypes. For VDR BsmI, the mean values for Z-score of the lumbar spine, neck, inter and total femur was greater in the bb genotype compared to BB and Bb genotypes. Logistic regression analysis revealed a significant association between femoral neck Z-score and VDR BsmI genotypes in an additive genetic model (unadjusted model (P = 0.035; Bb vs. bb), model 1 (adjusted for age and sex, P = 0.021; Bb vs. bb), model 2 (adjusted for age, sex and BMI, P = 0.013; Bb vs. bb) and model 3 (adjusted for age, sex, BMI and puberty, P = 0.011; Bb vs. bb, P = 0.049; BB vs. bb)) and dominant genetic model ((unadjusted model, P = 0.033; BB+Bb vs. bb), model 1 (adjusted for age and sex, P = 0.023; BB+Bb vs. bb), model 2 (adjusted for age, sex and BMI, P = 0.012; BB+Bb vs. bb and model 3 (adjusted for age, sex, BMI and puberty, P = 0.012; BB+Bb vs. bb)).

Conclusions: This investigation indicated that VDR BsmI polymorphism may be associated with BMD Z-score of the femoral neck but not the lumbar spine, in Iranian children and adolescents.