Etablissement Français du Sang Île-de-France, Paris, France, Ile-de-France, France
Background/Case Studies: The RH locus consists of 2 homologous genes, RHD and RHCE, encoding the D and C, E, c, e antigens, respectively. The molecular basis of the C/c polymorphism is due to 4 amino-acid substitutions, with c.307T >C (p.Ser103Pro) being considered the critical change. Some variant RHD alleles, e.g. RHDIIIa-CE(4-7)-D and RHD*DIVa, paradoxically demonstrate a weak C reactivity. Some RHCE*ce variant alleles also unexpectedly express a C reactivity. A rare RHCE variant, RHCE*01.39, corresponding to the c.308C >Tchange (p.Pro103Leu), was described in people of South-East Asia and found to be associated with an abolished c expression and unexpected C reactivity (Stegmann et al. Transfusion 2016). We describe here a novel allele, RHCE*ce308A, which also causes the loss of c expression and a weak C expression.
Study
Design/Methods: Rh typing was carried out by gel-test (monoclonal/polyclonal reagents). Genomic DNA was amplified by RHCE exon specific primers and sequenced.
Results/Findings: A 36-year-old male patient of African ancestry, with no particular medical history, was admitted to hospital for surgery. The serologic tests performed in the local laboratory revealed a negative antibody screen and a D+C+E-c-e+ phenotype, with a major discrepancy for C typing: 4+ with the Ortho column agglutination test (CAT) device (MS24 clone), but no reactivity with the Diagast microplate device (EM Technology, P3X255-13G8 + MS24 clones). The e reactivity was slightly weakened: 4+ with Ortho CAT device, 3+ with Diagast EM Technology. Samples were sent to our national reference laboratory. Sequencing of RHCE exons 1 to 10 showed a RHCE*CeRN allele and a RHCE*ce308A allele. A serologic study confirmed the weakening of the C antigen, potentially due to both RHCE*CeRN and RHCE*ce308A alleles. We found no weakening of e expression, and absence of E and c expression. The use of a panel of monoclonal anti-C reagents available from our collection showed, in gel-test (Bio-Rad), a 2+ and 1S+ reaction with the DGC02 and P3X255-13G8 clones, respectively (positive controls 4+). However, these 2 clones were nonreactive in a RNRN individual. Therefore, we can deduce that the RHCE*ce308A allele expresses C epitopes. In addition, the MS273 anti-C clone was nonreactive both in our patient and a RNRN individual. As a result, since the RN haplotype is known to encode a partial C antigen, RHCE*ce308A may also encode a partial C antigen. Conclusions: The RHCE*ce308A allele is not currently reported in genomic databases. The c.308C >A change (p.Pro103His), affecting the same amino-acid position than that considered critical for the C/c expression, appears to abolish the c antigen expression and to generate C epitopes, as was previously reported for the RHCE*ce308T allele. Besides, the RHCE*ce308A allele likely encodes a partial C antigen. However, we would recommend R1R1 RBC units as a first-line transfusion policy in this D+CpartialE-c-e+ patient.
