Mechanism 1: C in trans to RHD

Originally described as position effect or gene interaction effect, it is now known that in this mechanism the allele carrying RHD is in the trans (opposite haplotype) position to the allele carrying C. An example of the haplotype is Dce/dCe. The Rh antigen is normal but the arrangement is said to interfere with the expression of the D antigen on the cell membrane. This interference is not seen in the haplotype arrangement when the C gene is inherited in cis (same haplotype) position to RHD, as in the haplotype DCe/dce. Serologically the difference in the two haplotypes cannot be determined, however this is not needed because the D antigen is structurally complete. Therefore, these individuals may receive D-positive RBCs with no adverse effects.