CARD9 and inflammatory bowel disease: Genome-wide association studies (GWASs) in IgAN support that galactose-deficient IgA1 (Gd-IgA1) is heritable (3, 4), and they also suggest that some GWAS loci, such as CARD9, TNFSF13, and PSMB8, are shared among IgAN, inflammatory bowel disease (IBD), and bacterial infections (5).