TY - JOUR T1 - The role of genetic polymorphisms regulating vitamin D levels in rheumatoid arthritis outcome: a Mendelian randomisation approach JF - Annals of the Rheumatic Diseases JO - Ann Rheum Dis SP - 1430 LP - 1433 DO - 10.1136/annrheumdis-2013-204972 VL - 73 IS - 7 AU - Sebastien Viatte AU - Annie Yarwood AU - Kate McAllister AU - Shibeb Al-Mudhaffer AU - Bo Fu AU - Edward Flynn AU - Deborah P M Symmons AU - Adam Young AU - Anne Barton Y1 - 2014/07/01 UR - http://ard.bmj.com/content/73/7/1430.abstract N2 - Vitamin D has an important immunoregulatory function,1 ,2 and there is suggestive evidence for its role in the aetiology of autoimmune diseases, including rheumatoid arthritis (RA).3 Vitamin D levels are reduced in individuals with severe RA,4 ,5 but it is difficult to determine whether this reduction is cause or effect. The onset of arthritis during winter is associated with greater radiographic progression at 6 months, which would be compatible with a causative role.6 Single nucleotide polymorphisms (SNPs) in four vitamin D metabolism genes (GC, DHCR7/NADSYN1, CYP2R1 and CYP24A1) are associated at genome-wide significance with circulating vitamin D levels.7 ,8 Since vitamin D level is associated with RA severity, an association between those SNPs and RA severity would establish causality. Testing the association of genetic variants in genes that control circulating vitamin D levels provides, therefore, an instrument to obtain an unbiased test of the hypothesis that vitamin D levels are aetiologically linked to RA outcome by controlling unmeasured confounding (Mendelian randomisation9). Hence, we tested SNPs previously associated with vitamin D metabolism,7 ,8 and SNPs in these … ER -