Extended report Figure 1 Inﬂuence of interleukin 1 receptor antagonist (IL1RN) haplotypes on the age relationship to severity of knee osteoarthritis (OA). (A) The ﬁgure stratiﬁes patients with knee OA into thirds by age (<59, n=42; 59–68, n=40; >68, n=47). The numbers in each group are not exactly equal owing to the distribution of patients at the intersection of the groups. Patients within each age group were then stratiﬁed by carriage (dot-ﬁlled bars) or no carriage (grey-ﬁlled bars) of the IL1RN haplotype CTA of the single nucleotide polymorphisms (SNPs) rs419598/rs315952/rs9005. For each age strata and haplotype status, the frequency of severe radiographic knee OA (Kellgren–Lawrence (K–L) score >2) is plotted. (B, C) The joint space width (JSW) of each knee in patients with knee OA who do not (B) or do carry (C) the IL1RN CTA haplotype (rs419598/rs315952/rs9005) is plotted relative to age, and the regression line is shown for JSW relative to age. The JSW is signiﬁcantly associated with age (p=0.0059) in patients with knee OA who do not carry the IL1RN CTA haplotype, but not associated with age (p=0.56) in patients who carried one or two copies of the CTA haplotype. IL6 levels both in patients without the CTA haplotype (p=0.002 with exclusion of one outlier; mixed model considering two knees from an individual: p=0.04) and in patients with the CTA haplotype (p=0.029; mixed model: p=0.078). There was a pos- itive correlation between levels of IL10 and IL1ra levels only in samples from patients without the IL1RN CTA haplotype (p=0.0048; mixed model: p=0.056). No association was seen between levels of IL10 and IL1ra levels in patients who carry the IL1RN CTA haplotype (p=0.37; mixed model: p=0.55) This effect appears to be due in part to the fact that in the lower Ann Rheum Dis 2010;69:856–861. doi:10.1136/ard.2009.113043 859