Cindy Boer

Vitamin K Antagonist Anticoagulants and Osteoarthritis | 137 3.2 professionals for OA severity using Kellgren and Lawrence Grade (KLG)[15, 16] ( Sup- plementary Figure S1 ). Individuals which had at baseline locomotor disability were excluded from out study population[17] ( Supplementary Figure 1 ). We evaluated any OA progression, defined as an increase of KLG between baseline and follow-up of ≥1 and/or joint replacement; if baseline KLG was 0, progression was defined as increase of KLG ≥2 (incidence) [18]. Joints with a baseline KLG of 4 or baseline joint replacement were excluded from analysis ( Supplementary Figure S1 ). OA progression was defined in a joint- and side-specific manner (knee, hip; left and right). Joints with no progression of OA comprised the referent group. Joints with missing data were excluded ( Supple- mentary Figure S1 ), with the exception of joints with missing baseline data and a KLG of ≤1 at follow-up, which were included in the referent group ( Supplementary Figure S1 ). Vitamin K antagonists For each participant, we extracted the usage of VKAs (acenocoumarol) for the peri- od between baseline visit (RS-I-1, RS-II-1) and follow-up visits (RS-I-3, RS-II-2), from computerized pharmacy data ( supplementary text ). Acenocoumarol is the main pre- scribed VKA in the Netherlands as warfarin is not registered for use as a drug. All partic- ipants taking VKAs attended an anticoagulation clinic, which is standard practice in the Netherlands[19]. We excluded participants who were taking VKA (n=148) during the baseline visit to avoid prevalent user bias. We defined VKA usage as any acenocoumarol or usage during the period between the baseline (RS-I, RS-II) and follow-up visit (RS-I 3, RS-II 2), regardless of duration or dosage. To examine the effects of increasing duration of use, we defined duration of use by tertiles: ≤180 days, >180 days and ≤556 days, and, >556 days of use. Genetic data and haplotype analysis Methods for DNA-isolation, genotyping, quality control and data processing have been described elsewhere[10]. Data from 11 SNVs were extracted from the GWAS dataset: the MGP SNV previously found associated with OA[10] and ten SNVs needed for the VKORC1 H-haplotypes as described on the PharmGKB database[20] (Supplementa- ry Table S1). Haplotypes were inferred from all available genotypes(N=8,448), using genotype dosage data (HRC panel v.1.1[21]) and R-package haplo.stats[22]. Haplotypes were grouped based on VKA maintenance dose/ VKORC1 expression association; A: low dose VKA requirement/low VKORC1 expression and B: high dose VKA requirement/ high VKORC1 expression[23]. Study participants were further stratified into: low ex- pression/dose (AA), intermediate expression/dose (AB) and high expression/dose (BB) groups ( Table 1, Supplementary Table S1 ).