Background Low bone mineral density (BMD) is highly prevalent in patients with systemic lupus erythematosus (SLE). In different studies, lower vitamin D levels were associated with BMD loss [1, 2]. Also, serum vitamin D levels are lower in patients carrying the FF genotype of FOK-I vitamin D receptor (VDR) polymorphism [3]. Therefore, the VDR FOK-I polymorphism could be a possible determinant of BMD loss in SLE. However, the relationship between FOK-I VDR polymorphisms and BMD has not yet been studied in SLE patients.

Objectives To assess the relationship between FOK-I VDR polymorphisms and BMD in patients with SLE.

Methods Demographic and clinical data of 123 SLE patients were collected. Genotyping was performed by restriction fragment length polymorphism analysis of polymerase chain reaction amplified fragments (PCR-RFLP) [3], BMD measurements of the total hip and the lumbar spine were performed using dual energy x-ray absorptiometry at baseline and at follow-up. Statistical analyses were performed using χ-square test, independent samples t-test and ANOVA test for parametric measurements.

Results Of the 123 patients, (mean ± SD age 42.5±12.3 years, mean ± SD disease duration 8.9±7.8 years, 89% female, 72% Caucasian ethnicity), 47% carried the FF genotype, 39% carried the Ff genotype and 14% carried the ff genotype. Compared to patients with the FF and Ff genotypes, patients with the ff genotype had significantly higher mean BMD values (p=0.042), T-scores (p=0.007) and Z-scores (p =0.033) in the lumbar spine, but not in the hip. Mean ± SD follow-up duration since inclusion was 5.3±2.9 years. Mean BMD changes during follow-up were not significantly different between the three genotypic groups. In the subgroup of patients not taking vitamin D supplements (n=56), 25(OH)D serum levels were higher in patients with the ff genotype (mean 84.83 nmol/l, SD 26.2) compared to patients with the FF/Ff genotype (mean 58.90 nmol/l, SD 29.16) (p =0.043).

Conclusions BMD of the lumbar spine was significantly higher in SLE patients carrying the FOK-I VDR ff genotype compared to the other two genotypes. This association could in part be mediated by higher mean 25(OH)D levels in the FOK-I ff patients. The possible involvement of VDR gene polymorphisms in the development of osteoporosis in SLE needs further elucidation.

References

1. Bultink IE, Lems WF, Kostense PJ, Dijkmans BA, Voskuyl AE (2005) Prevalence of and risk factors for low bone mineral density and vertebral fractures in patients with systemic lupus erythematosus. Arthritis Rheum 52:2044-50

2. Jacobs J, Korswagen LA, Schilder AM, van Tuyl LH, Dijkmans BA, Lems WF, Voskuyl AE, Bultink IE (2013) Six-year follow-up study of bone mineral density in patients with systemic lupus erythematosus. Osteoporos Int 24:1827-33

3. Smolders J, Damoiseaux J, Menheere P, Tervaert JW, Hupperts R (2009) Fok-I vitamin D receptor gene polymorphism (rs10735810) and vitamin D metabolism in multiple sclerosis. J Neuroimmunol 207:117-21

Disclosure of Interest None declared

DOI 10.1136/annrheumdis-2014-eular.3553