BsmI vitamin D receptor's polymorphism and bone mineral density in men and premenopausal women on long-term antiepileptic therapy

Background: Utilization of antiepileptic drugs (AEDs) has long been associated with bone deleterious effects. Furthermore, the BsmI restriction fragment polymorphism of the vitamin D receptor (VDR) has been associated with reduced bone mineral density (BMD), mostly in postmenopausal women. This study evaluates the association between bone metabolism of patients with epilepsy and the BsmI VDR's polymorphism in chronic users of AEDs. Methods: This study evaluated 73 long-term users of antiepileptic drug monotherapy, in a cross-sectional design. Fasting blood samples were obtained to estimate the circulating serum levels of calcium, magnesium, phosphorus, parathormone, 25hydroxyvitamin D as well as the VDR's genotype. Bone mineral density at the lumbar spine was measured with Dual Energy X-Ray Absorptiometry. Results: Bone mineral density was significantly associated with the genotype of VDR (mean BMD: Bb genotype 1.056 +/- 0.126 g/cm2; BB genotype 1.059 +/- 0.113 g/cm2; bb genotype 1.179 +/- 0.120 g/cm2; P < 0.05). Additionally, the presence of at least one B allele was significantly associated with lower bone mineral density (B allele present: BMD = 1.057 +/- 0.12 g/cm2, B allele absent: BMD = 1.179 +/- 0.119 g/cm2; P < 0.01). Patients with at least one B allele had lower serum levels of 25hydroxyvitamin D when compared with bb patients (22.61 ng/ml vs. 33.27 ng/ml, P < 0.05), whilst they tended to have higher levels of parathyroid hormone. Discussion: Vitamin D receptor polymorphism is associated with lower bone mass in patients with epilepsy. This effect might be mediated through the vitamin D-parathormone pathway.