Cindy Boer

Cartilage Thickness and Hip Osteoarthritis | 81 2.1 ▲ Figure 3: mJSW and OA associated variants are co-localized with potential gene regulatory mark- ers . We examined the epigenetic histone marks in Chondrogenic cells, osteoblasts, hMSC, K562, HUVEC, HeLA and NHEK cells. This heatmap of the percentage of variants in gene regulatory regions (enhancer/ promoter associated regions) in high LD (r2 >0.8) with lead GWAS SNP. Enrichment was calculated according [25]. To the best of our knowledge, we are the first to scrutinize exome variants in relation to OA identified by large scale re-sequencing. We did not find low frequency exonic variants in any of the prioritized genes that could explain the observed associa- tions with mJSW. We do have to keep in mind that the power of the exome sequencing effort is smaller than the original discovery analysis. We were unable to examine vari- ants with allele frequencies below 0,07%. In addition, for rare or low allele frequen- cies, we only had power to detect relatively large effect sizes. For example, we had 80% power to detect a beta of 0,7 mm (almost 1SD) difference for a variant with 1% allele frequency. However, we tested all of the discovered exome variants in a multivariate analysis, and found that the novel identified rare exome variants did not affect the as- sociation between the GWAS-identified variants and mJSW in the same sample. This suggests that the associations between mJSW and the identified SNPs are not explained by rare exonic variants and likely exert their effects through regulation of expression. Indeed, supporting this hypothesis, we found that many these variants (or SNPs in LD) were annotated in regions that were annotated as regulatory active in chondroblastic and/or osteoblastic cells. However, more work is needed to examine the exact biological mechanism underlying the identified genetic loci. TGFA (Transforming Growth Factor Alpha, rs2862851) was the strongest novel locus associated with cartilage thickness and hip OA. TGFA has been suggested to be