Both genetic and environmental factors contribute to rheumatoid arthritis (RA) 
as well as osteoarthritis (OA). For RA, most of the known genetic markers are 
linked with genes from immunological pathways. Recent genome-wide association 
studies (GWAS) on RA identified known and novel susceptibility genes like 
HLA-DRB1, PTPN22, STAT4, TRAF1/C5, OLIG3/TNFAIP3, CD40, CCL21, MMEL1-TNFRSF14, 
CDK6, PRKCQ, IL2RB, and KIF5A-PIP4K2C. These association signals explain more 
than 50% of the genetic influence on RA. In contrast, less GWAS data for OA 
exist. Most OA susceptibility genes arose from classical candidate gene analyses 
and were not replicated in all study samples. Neuroendocrine factors are 
hypothesized to play an important role both in RA and OA etiology. Here, we 
discuss these findings and present an outlook for genetic association studies 
after GWAS.