Another example of haemopoietic (twin) chimaerism in a subject unaware of being a twin.

A fourth human blood group chimaera studies in Birmingham is an example of haemopoietic (twin) chimaerism in which the subject was unaware of being a twin. Chimaerism was discovered during routine antenatal serological investigation in which it was shown that the proposita has two red cell populations, one of the rhesus genotype rr, and the other R1r. Further studies showed that she has two populations of lymphocytes, one with the female karyotype, 46XX, and the other with the male karyotype, 46XY. Skin fibroblasts were all 46XX.

Sibship asymmetries of rhesus blood groups in the presence of maternal antibodies.

The genotypes of the children of R1r, R2r, and R1R2 fathers, and Rh-immunized rr mothers, were examined. R1r fathers had an excess of R1r over rr children, and R1R2 fathers had an excess of R1 r over R2r children. These asymmetries confirm the findings of a previous study. The possibilities of artefactual self-selection, of genotyping errors, and of errors in assigning paternity, were examined and excluded. Alternative models of genetic transmission and of antigenic structure were studied, but no basis for explaining the findings was found or formulated. Three possible biological explanations were formulated including (a) asymmetric segregation of the rhesus genes, (b) selective early fetal loss, and (c) a selective effect upon the performance of sperms bearing different haplotypes. The first of these three appeared unlikely. The data did not provide a basis for supporting or rejecting or differentiating the other two.

Computerization of a large antenatal serology service.

A computer scheme for a large antenatal serology service is described. A primary request form (for mother, father or child) has been developed. Standard reports are produced by the computer and are issued with a tear-off slip which should accompany subsequent specimens. Complicated reports are made by special letter. An instruction booklet is issued to all users. Information on patients and clinically significant antibodies is held in a special computer file and is regularly updated. The system provides an efficient and reliable day-to-day service and readily accessible data for retrospective research. A brief note on the computer elements of the system is provided.

Further observations on the Birmingham chimaera.

The appropriate ABH-gene specified glycosyltransferases in the plasma of the Birmingham chimaera were estimated. These observatiions and the demonstration of A1Leb blood group specific glycosphingolipid in the plasma indicate that the minority population of red blood cells probably represents the true blood groups of the patient.