Altered blood group expression in a patient with congenital rubella infection.

An infant with probable congenital rubella infection developed altered blood group expression. This was noted at 4 months of age. The child's blood was typed on seven separate occasions during the first 8 weeks of life as type A, but on repeat testing, her cells failed to agglutinate with anti-A and anti-A,B typing serum. The A antigen was present, however, because an eluate made after incubating her red cells with anti-A contained anti-A, and A antigen was demonstrated on buccal mucosa cells. Altered expression of blood group A (loss of agglutinability) has occurred previously only in association with hematologic malignancy.