Tanikawa et al. conducted a genome-wide association analysis in 7,035 individuals with duodenal ulcers and 25,323 controls from Japan. Two susceptibility loci were identified, one in the PSCA gene (which encodes prostate stem cell antigen) and one in the ABO blood group locus. Helicobacter pylori infection is a major cause of duodenal ulcers; these findings demonstrate that genetic variation might also have a role in their pathogenesis.