Cindy Boer

Hand Osteoarthritis Phenotypes | 103 2.2 Since no chromatin conformation capture data were available for chondrogenic or bone cells, we examined data from hu-man mesenchymal stem cells (hMSC), which are stem cell progenitors for chondrocytes and osteoblasts ( Figure 3g )[28]. The genomic location of rs1158850 ( Figure 3g, zone 2 ) appears to come into close proximity with the promoter region of WNT9A ( Figure 3g, zone 3 ). In addition, CTCF binding peaks in osteoblasts also intersect with the WN-T9A promoter region ( Figure 3f, zone 3 ), and are located near rs11588850 ( Figure 3f, zone 2 ). Next, differential expression analysis between OA lesioned and preserved carti- lage (hip/knee joints) identified WNT9A as the most significant result, with increased expression in OA lesioned cartilage (n=21, fold change=2.42, p-value=9.4x10 -08 , online S upplementary Table S2 ). Lastly, we examined whether rs11588850 may significantly affect (p-value<4.0x10 -08 ) the regulatory transcription factor (TF) binding motifs (37) located within the WNT9A promoter[35]. The minor allele (G) of rs11588850 is in high linkage disequilibrium (r 2 >0.8) with the OA risk increasing allele (G) of rs10916199, which significantly increases the binding affinity of the TF binding motif for RAD21 (G-allele LOD=11.2, A-allele LOD=9.8). The RAD21 protein has been previously shown to bind to the WNT9A promoter region ( online S upplementary Table S3). Thus, our results indicate WNT9A as novel OA associated gene, where rs1158850 is a potential regulatory variant for WNT9A ( Figure 3, zone 2-3 ). Additional hand osteoarthritis associated loci Osteoarthritis is highly heritable and co-occurrence of OA in multiple joint sites is well recognized[43]. As the hand joints are non-weight bearing, causes of OA in these joints may reflect effects of systemic risk factors, unlike the hip and knee joint where me- chanical loading is a dominant risk factor[7]. Thus, we examined whether other known OA loci may also confer risk for hand OA ( Figure 4 ). For 29 of the previously reported OA associated SNVs[13, 14], nominally significant associations (p-value<0.05) were ob- served for one or more hand OA phenotypes. Strong associations were seen for known- hand OA loci: ALDH1A2 -locus (rs3204689), MGP- locus (rs4767133)( Figure 4a and 4b ) and COG5 (rs3815148)[44], an SNV identified from a candidate gene study for hand OA. Interestingly, the MGP- and ALDH1A2 -loci, were only associated with finger and/or hand OA phenotypes, but not with thumb OA. In contrast, the BCL7A -locus (rs11059094), was only associated with thumb OA. Strikingly, several reported knee and hip OA loci were also associated with hand OA phenotypes in our study (Bonferroni, p-value<5.8x10-04): RUNX2 -locus (rs12154055), COL27A1 -locus (rs919642), ASTN2 -locus (rs13253416), IL11 -locus (rs4252548), TGFa -locus (rs3771501) and GDF5 -locus (rs143384)( Figure 4b ). Since some of these known loci