Vitamin D Receptor Gene Polymorphism and Bone Mineral Density in Hypercalciuric Calcium-Stone-Forming Patients

Abstract

Reduced bone mineral density (BMD) and an increased risk of vertebral fracture have been reported in calcium-stone-forming (CSF) patients presenting with idiopathic hypercalciuria. We investigated the association between BsmI vitamin D receptor (VDR) polymorphism and BMD in 68 hypercalciuric CSF patients (35 males and 33 premenopausal females, mean age ± SD = 39 ± 10 years). BMD was measured at lumbar spine (L₂–L₄) and femur neck sites using dual energy X-ray absorptiometry. A 72-hour dietary record and a 24-hour urine sample were obtained from each patient to determine calcium intake and excretion. The allelic frequency found for the sample as a whole was 16% BB, 44% Bb and 40% bb. Mean BMD values did not significantly differ among BB, Bb and bb patients at L₂–L₄ (1.162 ± 0.10, 1.133 ± 0.11 and 1.194 ± 0.19 g/cm², mean ± SD, respectively) or at neck sites (0.920 ± 0.11, 0.931 ± 0.15 and 0.982 ± 0.15 g/cm², respectively). Calcium intake and excretion were also not significantly different among the three genotypes. Patients were then divided into two groups, normal BMD, T-score ≧–1 (n = 34) and low BMD, T-score <–1 (n = 34), to further evaluate the allele influence on previous bone loss. Despite a trend for a higher mean BMD at spine or neck sites for patients with one or two b alleles when compared to BB patients, the difference did not reach statistical significance. The distribution of BB, Bb and bb genotypes in the low-bone-mass group (15, 47 and 38%, respectively) was similar to that in the normal-bone-mass group (18, 41 and 14%, respectively). These data suggest that BsmI VDR polymorphism does not play an important role in the bone loss seen in hypercalciuric CSF patients.