Two new cases of Rh mosaicism. Selective study of red cell populations

Somatic mosaicisms of chromosome 1 at two different stages of ontogenetic development detected by Rh blood group discrepancies

Spontaneous Rh blood group changes are a striking sign, reported to occur mainly in patients with hematologic disorders. Upon routine blood grouping, 2 unrelated individuals showed unexplained mixed red cell phenotype regarding the highly immunogenic c antigen (RH4), clinically relevant for blood transfusion and fetomaternal incompatibility. About half of their red cells were c-positive, whereas the other half were c-negative. These apparently hematologically healthy females had no history of transfusion or transplantation, and they tested negative for chimerism. Genotyping of flanking chromosome 1 microsatellites in blood, finger nails, hair, leukocyte subpopulations, and erythroid progenitor cells showed partial loss of heterozygosity encompassing the RHD/RHCE loci, spanning a 1p region of 26.7 or 42.4 Mb, respectively. Remarkably, in one case this was detected in all investigated tissues, whereas in the other, exclusively myeloid cells showed loss of heterozygosity. Both carried the RhD-positive haplotypes CDe and the RhD-negative haplotype cde. RHD/RHCE genotypes of single erythroid colonies and dual-color fluorescent in situ hybridization analyses indicated loss of the cde haplotype and duplication of the CDe haplotype in the altered cell line. Accordingly, red cell C antigen (RH2) levels of both propositae were higher than those of heterozygous controls. Taken together, the Rhc phenotype splitting appeared to be caused by deletion of a part of 1p followed by duplication of homologous stretches of the sister chromosome. In one case, this phenomenon was confined to myeloid stem cells, while in the other, a pluripotent stem cell line was affected, demonstrating somatic mosaicism at different stages of ontogenesis.

Measurements of the frequency of human erythrocytes with gene expression loss phenotypes at the glycophorin A locus

An assay method is described for determining the frequency of human erythrocytes having a gene expression loss phenotype at the glycophorin A locus presumably due to in vivo somatic mutational events in erythroid precursor cells. Monoclonal antibodies specific for the M and N glycophorin A alleles are used to identify variant cells that lack the expression of one allele in blood samples from MN heterozygotes. Flow cytometry and sorting are used to enumerate and purify variant cells. Using three different antibody combinations which are sensitive to the loss of either the M or the N allele, we find that variant cells occur at a frequency of 1 X 10(-5) in normal donors. We also detect variant cells with an apparent homozygous phenotype suggesting that events leading to homozygosity may occur at similar frequencies to gene loss events. Significant increases in variant cell frequency are observed in cancer patients after exposure to mutagenic chemotherapy drugs.

Automatized hemagglutination kinetics

An automatized technique for the study of hemagglutination kinetics is described. It was used to differentiate between homozygous and heterozygous individuals in the Rh system. Other applications are proposed.

Erythrocyte membrane modification in malignant disease of myeloid and lymphoreticular tissues. II. Erythrocyte "mosaicism" in acute erythroleukaemia

A case of acute erythroleukaemia is described. The patient's RBC, which at first appeared to be a mixture of groups B and O, were shown in fact to be a mixture of normal B and very weak B.

Erythrocyte membrane modification in malignant diseases of myeloid and lymphoreticular tissues. I. Tn-polyagglutination in acute myelocytic leukaemia

Tn polyagglutination (persistent mixed-field polyagglutination) occurring in a patient with an acute myelocytic leukemia is described. The association of this RBC membrane change, thought to be due to somatic mutation at stem cell level, with a myeloproliferative disorder, has not been previously reported.