Studies on blood from the original Rhnull proposita and relatives

A relative of the original Rh proposita, of group R1R2, shows weak expression of his Rh antigens, and is thought to be an Rhnull heterozygote. His wife and 3 of their 4 children show normal Rh antigen expression, but one daughter showed weak Rh antigen expression, as determined by quantitative haemagglutination. The observations support the proposition that the father is heterozygous for an unlinked modifier of Rh antigen expression. Stomatocytosis, observed in the Rhnull proposita and other Rhnull individuals, was also observed, but to a lesser degree, in the blood of an other individual thought to be an Rhnull heterozygote. This observation also supports the earlier conclusion that the Rhnull phenotype of the proposita is due to homozygosity for inactive alleles at a locus which controls the biosynthesis of precursor for Rh and LW antigens. Osmotic fragility tests showed that the Rhnull cells were more fragile than cells with normal Rh antigen expression, and cells from Rhnull heterozygotes had intermediate fragility. This is consistent with the proposition that Rh antigens are normal structural components of the red cell membrane, and the Rhnull heterozygotes show a deficiency of the Rh antigenic structures.