Clinically relevant RHD-CE genotypes in patients with sickle cell disease and in African Brazilian donors.

BACKGROUND: As a consequence of the homology and opposite orientation of RHD and RHCE, numerous gene rearrangements have occurred in Africans and resulted in altered RH alleles that predict partial antigens, contributing to the high rate of Rh alloimmunisation among patients with sickle cell disease (SCD). In this study, we characterised variant RH alleles encoding partial antigens and/or lacking high prevalence antigens in patients with SCD and in African Brazilian donors, in order to support antigen-matched blood for transfusion. MATERIAL AND METHODS: RH genotypes were determined in 168 DNA samples from SCD patients and 280 DNA samples from African Brazilian donors. Laboratory developed tests, RHD BeadChip(TM), RHCE BeadChip(TM), cloning and sequencing were used to determine RHD-CE genotypes among patients and African Brazilian blood donors. RESULTS: The distributions of RHD and RHCE alleles in donors and patients were similar. We found RHCE variant alleles inherited with altered RHD alleles in 25 out of 168 patients (15%) and in 22 out of 280 (7.8%) African Brazilian donors. The RHD and RHCE allele combinations found in the population studied were: RHD*DAR with RHCE*ceAR; RHD*weak D type 4.2.2 with RHCE*ceAR, RHD*weak D type 4.0 with RHCE*ceVS.01 and RHCE*ceVS.02; RHD*DIIIa with RHCE*ceVS.02. Thirteen patients and six donors had RHD-CE genotypes with homozygous or compound heterozygous alleles predicting partial antigens and/or lacking high prevalence antigens. Eleven patients were alloimmunised to Rh antigens. For six patients with RHD-CE genotypes predicting partial antigens, no donors with similar genotypes were found. DISCUSSION: Knowledge of the distribution and prevalence of RH alleles in patients with SCD and donors of African origin may be important for implementing a programme for RH genotype matching in SCD patients with RH variant alleles and clinically significant Rh antibodies.

Variant RH alleles and Rh immunisation in patients with sickle cell disease.

BACKGROUND: Alloimmunisation is a major complication in patients with sickle cell disease (SCD) receiving red blood cell (RBC) transfusions and despite provision of Rh phenotyped RBC units, Rh antibodies still occur. These antibodies in patients positive for the corresponding Rh antigen are considered autoantibodies in many cases but variant RH alleles found in SCD patients can also contribute to Rh alloimmunisation. In this study, we characterised variant RH alleles in 31 SCD patients who made antibodies to Rh antigens despite antigen-positive status and evaluated the clinical significance of the antibodies produced. MATERIALS AND METHODS: RHD and RHCE BeadChip™ from BioArray Solutions and/or amplification and sequencing of exons were used to identify the RH variants. The serological features of all Rh antibodies in antigen-positive patients were analysed and the clinical significance of the antibodies was evaluated by retrospective analysis of the haemoglobin (Hb) levels before and after transfusion; the change from baseline pre-transfusion Hb and the percentage of HbS were also determined. RESULTS: We identified variant RH alleles in 31/48 (65%) of SCD patients with Rh antibodies. Molecular analyses revealed the presence of partial RHD alleles and variant RHCE alleles associated with altered C and e antigens. Five patients were compound heterozygotes for RHD and RHCE variants. Retrospective analysis showed that 42% of antibodies produced by the patients with RH variants were involved in delayed haemolytic transfusion reactions or decreased survival of transfused RBC. DISCUSSION: In this study, we found that Rh antibodies in SCD patients with RH variants can be clinically significant and, therefore, matching patients based on RH variants should be considered.