Risk factors for osteoporosis after renal transplantation and effect of vitamin D receptor Bsm I polymorphism

Objective

Rapid loss of vertebral or hip mineral density after renal transplantation is a major complication which occurs within 6-12 months. The aim of this study was to evaluate risk factors contributing to bone disease in the early stage after renal transplantation and the effect of vitamin D receptor (VDR) gene polymorphisms.

Methods

We prospectively followed for up to 12 months 44 patients (29 men and 15 women) with end-stage renal disease who underwent kidney transplantation. All patients received prednisone with either cyclosporine (CsA)/mycophenolate mofetil (MMF) or tacrolimus (Tac)/MMF therapy. Spine, hip, and whole body bone mineral density (BMD) was measured at 12 months after transplantation. According to World Health Organization recommendations, our patients were categorized as normal, osteopenic, or osteoporotic BMD levels. VDR alleles were genotyped as BB, Bb, or bb by polymerase chain reactions based on polymorphism at the Bsm I restriction site.

Results

Forty-six percent of patients were normal, 43% osteopenic, and 11% osteoporotic. Significant risk factors for osteoporosis among renal transplant recipients were younger age and pretransplant high intact parathyroid hormone (iPTH) levels. (P values .045 and .027, respectively). According to polymorphic group categorization, posttransplant serum Ca was significantly higher in patients with BB or Bb genotype than in those with bb genotype (P = .012). Although there was no statistical significance regarding iPTH levels, it was higher among Bb+BB than the bb genotype group. Also, first-year BMD analysis after transplantation according to Bsm I polymorphism showed significant differences in femur BMD levels according to the dual classification of polymorphism (P < .05). The BMD levels in the bb group was higher than in the Bb+BB group.

Conclusions

Although high pretransplant iPTH levels and younger age enhanced posttransplant bone loss, functionally different alleles of the VDR gene may modulate bone turnover during the first year after renal transplantation.