Decode scientists have found one such instance. They report in Friday’s Nature that a DNA variant increases a person’s risk of Type 2 diabetes by 30 percent if inherited from the father, but reduces the risk by 10 percent if comes from the mother.
Because the two effects tend to cancel each other out, they have not been picked up by the standard tests that do not identify the parental origin of each section of DNA.
DeCode found that five of seven variants tested made different contributions to disease depending on the parent of origin. In most cases the effect was of differing degrees of severity, depending on the parent involved.
How odd! I can't imagine why this is the case.