The ulcer inducing bacteria, Helicobacter pylori, adapts to the blood group of people. This is what some researchers have announced that South American Indians have so many ulcers and stomach cancers.
To infect the stomach, the bacteria attach to the stomach wall, specifically to the same antigen that defines blood groups. The current study has clarified that in populations where all blood groups are mixed, the bacteria are associated with anyone without distinction. In indigenous populations in South America, the bacteria are only associated with blood group O antigen. That is the most important blood group.
Researchers have discovered which gene is related to the blood antigen and have seen that in both cases the sequence of this gene is not exactly the same. It follows that the bacteria of the indigenous populations of South America have adapted to the predominant blood group in the area and hope that this discovery will serve to find better treatments.