The first example of anti-Diego(b) found in a Polish woman with the Di(a+b-) phenotype and haemolytic disease of the newborn not requiring treatment.

All pregnant women with anti-Diegob (anti-Dib) described so far were non-Caucasians. We present the case of a Polish Di(a+b-) woman with anti-Dib, which did not bind complement, was immunoglobulin G3 (IgG3) alone and had very low functional activity. She delivered a Di(a+b+) infant with a positive direct antiglobulin test and the antibody in his serum but very mild haemolytic disease. Both parents of the pregnant woman were Di(a+b+), so were all her three children. The whole family have been living in a small village in southeastern Poland for a long time. The rare Diego phenotypes, found now and previously in Poland, suggest gene admixture introduced as a result of Poland being invaded by Mongolian-background Tatars during the past centuries.