Relationship between Rh-o(D) zygosity and red cell Rh-o(D) antigen content in family members

The red cells of 63 members of 11 families were tested with (125)I-labeled anti-Rh(0)(D). Families with a history of hemolytic disease of the newborn due to fetomaternal Rh incompatibility were selected for study. In such families it was possible to determine the antibody binding to the Rh(0)(D) heterozygous red cells of the children and to compare within each family this value with the antibody bound to the father's Rh(0)(D)-positive red cells and the mother's Rh(0)(D)-negative red cells. The fathers in all the families studied could be assigned to two classes on the basis of the quantity of antibody bound to their red cells. One group bound about the same quantity of antibody to their cells as did their children, indicating that they were heterozygous for the Rh(0)(D) antigen. The other bound about twice as much antibody to their cells as did their children, indicating that they were homozygous for the antigen. The Rh genotype of the father in all 11 families could be ascertained by using the children in each family as a reference point. The members of two families showed a poor correspondence between antibody binding and zygosity. In one family an Rh heterozygous child (R(1)r) took up 85% of the antibody bound to the father's homozygous cells (R(1)R(1)), and in the other family an Rh heterozygous child (R(1)r) took up 20% more antibody than did the cells of her father, which were of the same Rh phenotype (Rh(1)) and zygosity.The quantity of antibody bound to the red cells of unrelated Rh(0)(D) homozygous individuals of the same Rh phenotype (Rh(1)) showed an almost sixfold variation. A consequence of this observation was that the cells of Rh(0)(D) heterozygous children of high antibody uptake fathers took up more antibody than did the cells of low antibody uptake Rh(0)(D) homozygous fathers. The gene dosage effect for the Rh(0)(D) antigen demonstrable within a family does not appear to apply when unrelated individuals are tested, even though they may be of the same Rh phenotype.