Genotypes compared GG vs GT/TT CC vs CT/TT GG vs GC/CC CC vs CT/TT CC vs CT/TT GG vs GA/AA TT vs CT/CC CC/CT vs TT GG vs GA/AA Haplotype C,T,A (1 or 2 copies) vs no copies GG vs GA/AA CC vs CT/TT CC vs CT/TT CC vs CA/AA TT vs CT/CC AA vs AG/GG NYUHJD population (n=80*) Kellgren–Lawrence score >2 (odds ratio (CI)) 1.26 (0.48 to 3.28); p=0.63 0.89 (0.32 to 2.47); p=0.82 1.96 (0.75 to 5.11); p=0.17 1.25 (0.45 to 3.48); p=0.68 1.36 (0.53 to 3.47); p=0.52 1.12 (0.43 to 2.91); p=0.81 0.49 (0.175 to 1.37); p=0.174 0.46 (0.15 to 1.20); p=0.113 0.25 (0.091 to 0.680); p=0.0067‡ 0.29 (0.09 to 0.93); p=0.037† 1.37 (0.040 to 4.70); p=0.62 3.00 (0.87 to 10.34); p=0.081 3.32 (1.08 to 10.28); p=0.037 3.32 (1.08 to 10.28)§; p=0.037 0.57 (0.22 to 1.49); p=0.25 0.48 (0.18 to 1.25); p=0.13 Duke POP study (n=50) Kellgren–Lawrence score >2 (odds ratio (CI)) 0.031 (0.004 to 0.27); p=0.0016† 0.32 (0.090 to 1.00); p=0.071 0.084 (0.02 to 0.343); p=0.0006† 0.031 (0.004 to 0.270); p=0.0016† Table 2 Genotype association with radiographic severity of knee osteoarthritis (OA) in two populations Extended report Gene IL1A(+4845) IL1B(−511) IL1B(−1464) IL1B(−3737) IL1B(+3954) IL1B(+3877) IL1RN(+2018) IL1RN IL1RN IL1RN haplotype TNFA(−308) IL10(−1082) IL10(−819) IL10(−592) ESR1_PvuII ESR1_Xbal rs Number rs17561 rs16944 rs1143623 rs4848306 rs1143634 rs1143633 rs419598 rs315952 rs9005 rs419598/rs315952/ rs9005 rs1800629 rs1800896 rs1800871 rs1800872 rs2234693 rs9340799 Genotype or haplotype IL1RN rs419598 0.35 CC/TC IL1RN rs315952 0.53 TT IL1RN rs9005 0.45 AA/GA IL1RN rs419598/ rs315952/rs9005 0.32 Carriage of Haplotype C,T,A Results in bold indicate signiﬁcant association with decreased risk for severe OA. *Number of Caucasian patients with knee osteoarthritis who met inclusion criteria and had complete genotype data. †IL1RN single nucleotide polymorphisms (SNPs) of interest from the NYUHJD population were then tested in the Duke POP population, and common haplotypes in the IL1RN gene were tested in both populations. p Values <0.05 were considered statistically signiﬁcant. All other SNPs tested in the NYUHJD population were subsequently evaluated in the POP patients, and none were signiﬁcant (data not shown). ‡For each single SNP, p values <0.027 were considered statistically signiﬁcant to account for multiple comparisons in the discovery population (NYUHJD) involving 15 SNPs. §IL10(−819) and IL10(−592) alleles were completely concordant in this population. NYUHJD, New York University Hospital for Joint Diseases; POP, Prediction of Osteoarthritis Progression study. Table 3 Interleukin 1 receptor antagonist (IL1RN) genotype association with two radiographic parameters of severity in the combined populations Frequency of indicated genotype or haplotype* Kellgren–Lawrence score >2 (odds ratio (CI))† (N=130) 0.22 (0.091 to 0.508); p=0.0005 3.83±1.91 (n=89) 0.44 (0.21 to 0.92); p=0.0297 3.69±1.80 (n=132) 3.11±2.01 (n=117) 0.15 (0.065 to 0.349); p<0.0001 3.86±1.71 (n=114) 3.04±2.01 (n=135) 0.14 (0.053 to 0.368); p< 0.0001 3.99±1.77 (n=80) 3.14±1.93 (n=169) Joint space width (JSW in mm)‡ (mean±SD) Test genotype Reference genotype 3.19±1.88 (n=162) p Value§ 0.036 0.069 0.0063 0.0008 *Frequency within the total patients (n=130 with complete genetic data) with knee osteoarthritis (OA) from two separate populations (NYUHJD; Duke POP Study). †Odds ratio for severe OA, as measured by Kellgren–Lawrence (KL) score, comparing the indicated genotype or haplotype with all other genotypes for that single nucleotide polymorphism. Patients were classiﬁed by radiographic severity of knee OA by stratifying the KL scores to compare KL=1 or 2 vs KL=3 or 4. Similar signiﬁcant associations were found when patients were stratiﬁed so that KL=1 was compared with KL=2–4 (data not shown). ‡The smaller JSW in millimetres for each knee was included in the knee-based analysis (n=251 knees with complete data in 126 patients from the NYUHJD and Duke POP populations). Statistical analysis was adjusted for age, gender and body mass index in a mixed model analysis of variance for intercorrelated data to adjust for the subject effect on two knees. §Wilcoxon test. NYUHJD, New York University Hospital for Joint Diseases; POP, Prediction of Osteoarthritis Progression study. CTA haplotype=2.74 mm±2.21, vs reference haplotypes=2.23 mm±1.67; p=0.53). Since age has strong epidemiological associations with prevalence and severity of knee OA and was associated with severity in the combined studies, we evaluated the interac- tion between age and IL1RN genotype relative to severity. In regression models, there was a signiﬁcant interaction between genotype and age (p<0.0001) relative to KL scores, with the effect of genotype being stronger at greater ages. The addi- tion of the IL1RN haplotype to regression models that included age provided a better ﬁt than with age alone (p<0.0001). To examine the effect of genotype at different ages, we divided the population into age tertiles. Carriers of the CTA IL1RN haplotype were at signiﬁcantly lower risk for severe KL scores in each age group (ﬁgure 1A). In regression models, age was 858 associated with KL>2 in patients without the CTA haplotype (p=0.032) but not in those carrying the haplotype. Similarly, age was associated with JSW narrowing only in patients with knee OA who do not carry the CTA haplotype (ﬁgure 1B vs ﬁgure 1C). Given that IL1RN alleles have been associated with different expression levels of inﬂammatory mediators, we evaluated the inﬂuence of the IL1RN CTA haplotype on inﬂammatory media- tors in SF from the POP study (n=50). Patients carrying the IL1RN CTA haplotype had signiﬁcantly lower SF mean levels of IL10 (p=0.034), and showed a trend towards lower levels of IL1β and IL6 (table 4). No differences by IL1RN haplotype were seen for IL1Ra protein, monocyte chemotactic protein-1, mac- rophage inﬂammatory protein-1β, C-reactive protein or COMP (table 4). IL1Ra protein levels were positively correlated with Ann Rheum Dis 2010;69:856–861. doi:10.1136/ard.2009.113043