Association between vitamin D receptor polymorphisms and systemic lupus erythematosus in an Indian cohort

Systemic lupus erythematosus (SLE) is an autoimmune disorder with various clinical manifestations. Susceptibility to development of SLE has been linked to several factors, such as genetic, environmental and hormonal. Vitamin D appears to have a regulatory role on disease manifestation and activity. Vitamin D exerts its effect through vitamin D receptors (VDR). Several studies have demonstrated an association between VDR polymorphisms and susceptibility to SLE in different populations, although the results are still inconclusive. In the present study, we investigated the association of VDR polymorphisms with SLE in a cohort of patients from Odisha, India.

Female SLE patients (n = 331) who fulfilled the revised American College of Rheumatology classification criteria were enrolled along with 282 healthy controls from similar geographical areas. VDR polymorphisms (BsmI, ApaI, TaqI and FokI) were typed by polymerase chain reaction followed by restriction fragment length polymorphism. Plasma level of 25-OH vitamin D was quantified by enzyme-linked immunosorbent assay.

Prevalence of FokI (Ff) and TaqI (Tt) heterozygotes were significantly higher in SLE patients compared to healthy controls (Ff: P < 0.0001, odds ratio [OR] = 2.80, 95%CI = 1.99-3.95; Tt: P < 0.0001, OR = 2.07, 95%CI = 1.49-2.89). Furthermore, the minor alleles of FokI (f) and TaqI (t) polymorphisms were also more frequent in SLE patients than healthy controls (f: P < 0.0001, OR = 1.96, 95%CI = 1.52-2.52; t: P = 0.0002, OR = 1.60, 95%CI = 1.25-2.09).

FokI and TaqI variants are significantly associated with SLE in an eastern Indian cohort. The cause-effect relationship can be assessed from the combined analyses of VDR polymorphism, plasma vitamin D levels and clinical manifestations.