Lastly, GCH1 rs3783637(C), associated at p = 2 × 10−6 (OR = 1.10) in a GWAS conducted in a Japanese population of RA (Okada et al., 2012), was associated (p < 0.05) with CD in this study for the opposite allele “T.” This evidence concerns the gene GCH1 and rheumatoid arthritis.