Hemolytic disease of the newborn due to anti-PP1 P k (anti-Tj a).

A newborn infant of genotype P2p suffering from ABO-like hemolytic disease was born to a mother of the very rare genotype pp. The disease was severe enough to require exchange transfusions with pp blood. The mother and other members of the family with the same rare pp blood provided compatible donor blood for transfusions of the mother herself and for replacement transfusion of her affected infant. The mothers serum contained IgM molecules and also IgG molecules capable of crossing the placenta to induce a hemolytic process on the infant's red blood cells. The genotype of the P1 negative father was very likely P2P2 so that the genotype of the affected infant had to be P2p. A search of the literature revealed an earlier report from Japan in which the genotype of the P1 positive father was P1P2. As was to be expected the genotype of this affected infant was P2p.