Vitamin-D receptor genotype and renal disorder in Japanese patients with systemic lupus erythematosus

Background/aims: It is known that allelic variants of the gene encoding the vitamin-D receptor (VDR) detected by BsmI increase the risk of some advanced malignant tumors, suggesting that such variants may cause functional differences in 1,25(OH)(2) vitamin D(3). We examined the VDR genes of Japanese systemic lupus erythematosus (SLE) patients, to determine whether different genotypes are correlated with SLE or its criteria.

Methods: VDR genotyping of 58 unrelated Japanese SLE patients was performed based on polymerase chain reaction-restriction fragment length polymorphism (RFLP). Following amplification, products were digested with BsmI. The RFLPs were coded as Bb, where the uppercase letter signifies the absence of the digested site and the lowercase letter signifies the presence of the site.

Results: The frequency of the VDR BB genotype was significantly higher in SLE patients (15.5%, n = 9/58, p < 0.0001) than in controls (5.7%, n = 5/87). Furthermore, a larger proportion of bb individuals was observed among patients with nephrotic syndrome (61.5%, n = 8/13) than among SLE patients without renal dysfunction (35.7%, n = 10/28). There was a significant tendency for the population of patients with the bb genotype to be correlated with that of patients with renal dysfunction (p = 0.0304).

Conclusion: These findings suggest that the BB genotype might trigger the development of SLE, and that the bb genotype is associated with lupus nephritis.