RHD alleles among pregnant women with serologic discrepant weak D phenotypes from a multiethnic population and risk of alloimmunization

Abstract

Background A considerable number of RHD alleles responsible for weak and partial D phenotypes have been identified. Serologic determination of these phenotypes is often doubtful and makes genetic analysis of RHD gene highly desirable in transfusion recipients and pregnant women. We analyzed the RHD gene in a cohort of pregnant women with doubtful D phenotypes. Methods RHD genotyping was performed on 104 cases with D typing discrepancies or with history of serologic weak D phenotype. Laboratory‐developed DNA tests, RHD BeadChip (Bioarray Solutions, Immucor), and sequencing were used to identify the RHD alleles. Results Molecular analyses showed 23 of 104 (22%) pregnant women were RHD*weak D types 1, 2, or 3 and not at risk for anti‐D. Fifty‐one (49%) were RHD*weak partial 4.0, 6 RHD*weak D type 38 (6%), 1 RHD*weak D type 45 (1%), 1 RHD*weak D type 67 (1%), and potentially at risk for being alloimmunized and making anti‐D. Partial D was identified in 22 of 104 (21%) patients and definitively at risk for anti‐D. Discussion Appropriate classification of RhD phenotypes is recommended for correct indication of RhIG in pregnant women. However, the serologic distinction between RhD‐negative and RhD‐positive phenotypes is a difficult task in the case of D variants due to the variations in serologic testing. Our results show a great variability in RHD variant alleles in pregnant women from this population of high admixture. According to these results, 78% of these obstetric patients are at risk for anti‐D and candidates for RhIG.

High frequency of variant RHD genotypes among donors and patients of mixed origin with serologic weak‐D phenotype

“…*The reason for recommending the transfusion of D-positive units for individuals bearing these variants was based on the lack of alloimmunization reports rather than on definite evidences that they are not prone to anti-D development performing the molecular investigation. 11,25 All studies were concordant with respect to the high prevalence of RHD*DAR and to the relatively lower representability of RHD*weak D types 1, 2, and 3 among…”

“…Previous studies have also evaluated the frequency of D variants among Brazilian donors and patients, but with different criteria for performing the molecular investigation . All studies were concordant with respect to the high prevalence of RHD*DAR and to the relatively lower representability of RHD*weak D types 1, 2, and 3 among Brazilian donors with weak‐D phenotype.…”

“…This finding justifies why UK guidelines determine that patients exhibiting weak results in the D typing routine should be treated as D+ unless they are a female of childbearing age or a patient under chronic transfusion support . However, studies evaluating patients of mixed origin with discrepancies in D typing have shown that the distribution of RH variant alleles significantly differ from that observed among European‐descent individuals, mainly referring to the partial‐D phenotype, but also concerning the weak‐D phenotype . Transposing the recommendation of European transfusion guidelines to this different scenario may cause anti‐D alloimmunization, especially in services with no access to RH genotyping.…”

“…9 However, studies evaluating patients of mixed origin with discrepancies in D typing have shown that the distribution of RH variant alleles significantly differ from that observed among European-descent individuals, mainly referring to the partial-D phenotype, but also concerning the weak-D phenotype. 10,11 Transposing the recommendation of European transfusion guidelines to this different scenario may cause anti-D alloimmunization, especially in services with no access to RH genotyping.…”

A serologic weakly reactive RhD is caused by a novel RHD (c.722C>A, p.Thr241Asn) allele

“…This amino acid change was predicted within the eighth membrane passage. Review of previously reported RHD variants at p.241 showed two known D variants: RHD*weak D type 67 (c.722C>T, p.Thr241Ile) associated with a cDE haplotype 2 and RHD*DEL45(c. 721A>C,p.Thr241Pro, which resulted in extremely weakened D expression) 3 . These three amino acid replacements were predicted to have a “deleterious effect” on protein function by PROVEAN and being “probably damaging” by PolyPhen2.…”