RHCE Gene Research Articles

Molecular genetics and clinical applications for RH

Rhesus is the clinically most important protein-based blood group system. It represents the largest number of antigens and the most complex genetics of the 30 known blood group systems. The RHD and RHCE genes are strongly homologous. Some genetic complexity is explained by their close chromosomal proximity and unusual orientation, with their tail ends facing each other. The antigens are expressed by the RhD and the RhCE proteins. Rhesus exemplifies the correlation of genotype and phenotype, facilitating the understanding of general genetic mechanisms. For clinical purposes, genetic diagnostics of Rhesus antigens will improve the cost-effective development of transfusion medicine.

Weak D prevalence among Indian blood donors

Weak D prevalence among Indian blood donors

Specific amino acid substitutions cause distinct expression of JAL (RH48) and JAHK (RH53) antigens in RhCE and not in RhD

Westhoff and colleagues1 and Hustinx and coworkers2 have recently reported a total of three molecular causes for the low-prevalence Rh antigen JAL (RH48). Quantitative weakening and qualitative effects are documented for these variant RhCE proteins. Similar serological effects have been observed in the JAHK+ (RH53),3 ceSL,4 and RhCe(S122P)5 variants of the RhCE protein. We have observed 4 RhD variants harboring similar amino acid substitutions at positions 114 or 122 (Table 1). Table 1 RHD alleles encoding amino acid substitutions at positions 114 and 122 Most Rh antigens are known to be associated with molecular variants of either the RHD or RHCE gene. However, distinct Rh antigens, like c (RH4), G (RH12), Rh32 (RH32), Evans (RH37) and FPTT (RH50), can be expressed by RhD and RhCE variants (Table S1, available online). We collated all low-prevalence Rh antigens caused by single nucleotide substitutions and identified pairs of RHD and RHCE alleles that harbor identical substitutions (Table S2, available online).1–4,6 Only amino acid substitutions at positions 114 and 122 were currently found to fulfill both criteria. In RhCE these substitutions cause JAL or JAHK antigen expression. Hence, we assessed the possible expression of JAL and JAHK by RhD proteins harboring similar amino acids at positions 114 or 122. A DVII sample harboring a substitution at 110 was used as negative control. All RhD samples with amino acid substitutions at position 114, weak D type 17, type 25 and type 47, were negative for the JAL antigen (Table 2). The CeMA and Rhce(R114Q) control samples were JAL positive, as expected. Because the antigen density of weak D type 17 is very low (Table 1), we corroborated its lack of JAL expression by a negative adsorption-elution test (not shown). Table 2 Serologic results of RhD and RhCE variants with amino acid substitutions at positions 114 and 122 The weak D type 54 sample with an amino acid substitution at position 122 was negative for the JAHK antigen (Table 2). The RhCe(S122L) control sample was positive with the 3 anti-JAHK sera, as expected. ceSL has been reported to be JAHK negative.4 We confirmed this result with the original red blood cell (RBC) samples and the anti-JAHK P4.53A serum used previously. However, the two anti-JAHK sera of greater titer revealed that ceSL samples were in fact JAHK positive (Table 2). Both RhCe(S122P) samples were JAHK negative with all 3 sera. The two sera P4.53B and P4.53C were identified from a series of 138 samples collected from pregnant women with a positive antibody screen.7 Both women had neither been transfused nor were their newborns or the putative fathers positive for the JAHK antigen.7 Hence, anti-JAHK is possibly a rather frequent, naturally occurring antibody associated with pregnancy. The titers of anti-JAL (Table 2) determined with CeMA and Rhce(R114Q) differed in congruence with the known weaker expression of JAL in the Rhce variants Rhce(R114Q) and ces(340) compared to the RhCe variant CeMA.2 In contrast to Rhce(R114Q) harboring Gln114, ces(340) and CeMA are caused by mutations encoding for Trp114.1,2 The model presented by Westhoff et al.1 suggests conformational changes due to Trp114 that contribute to the expression pattern of the JAL antigen. The weak JAL expression in Rhce(R114Q) may be due to the different biochemical properties of Trp (W) and Gln (Q). However, the JAL expression in ces(340), which also harbors Trp114, is distinctly weaker than in CeMA and, hence, requires a different molecular explanation (Table S3, available online):1,2,8 The additional Leu245Val substitution, known to cause a weak expression of the e antigen,8 could also induce the weak expression of the JAL antigen. Currently observed alleles cannot exclude the possibility that the weak JAL expression in both Rhce variants is caused by the 4 amino acid residues at positions 48, 60, 68, and 103, which typically differ between the RhCe and Rhce proteins. We conclude that JAL and JAHK antigens are expressed by Ce and ce variants of the RhCE protein. We found that neither antigen was expressed by any of the 4 RhD protein variants possessing similar amino acid substitutions at positions 114 and 122.

Molecular biology of the Rh system: clinical considerations for transfusion in sickle cell disease

The last decade has witnessed an abundance of information detailing the genetic diversity of the RH locus which has exceeded all estimates predicted by serology. Well over 120 RHD and over 60 different RHCE alleles have been documented, and new alleles are still being discovered. For clinical transfusion medicine, RH genetic testing can now be used to determine RHD zygosity, resolve D antigen status, and detect altered RHD and RHCE genes in individuals at risk for producing antibodies to high-incidence Rh antigens, particularly patients with sickle cell disease (SCD).

Fiber-FISH Analysis Revealed Genomic Variations in the RHD as a Cause of Serologically Rh-negative Phenotype

The human Rhesus (Rh) blood group is determined by 2 highly homologous RH genes, RHD and RHCE. These genes are located on chromosome 1p36.1, a genomic region representing copy number variation. In Rh-positive individuals, both RHD and RHCE genes are present, while in most Rh-negative individuals RHD genes are missing and are homozygous for a single RHCE gene. Some individuals with a serologically Rh-negative phenotype were diagnosed to be RHD-gene positive by a locus-specific DNA assay using polymerase chain reactions with sequence-specific primers (PCR-SSP). Therefore, the current PCR-based assay, examining the presence or absence of partial sequences of RHD genes, does not necessarily produce correct typing results. Alterations in the genomic structure of RHD that cause negative gene expressions are difficult to detect by the PCR-based assay because of highly homologous sequences of the 2 RH genes. In the present study, we examined, by extended chromatin fiber fluorescence in situ hybridization (fiber-FISH) with 2 DNA probes for introns 3 and 7 of the RH genes, the genomic structure of the RH gene region in 6 Rh-negative Japanese donors whose genotype was diagnosed as RHD-gene positive by the PCR-SSP assay. We demonstrated that varied sizes of deletion and/or insertion in the RH loci caused the Rh-negative phenotype.

Preliminary results of fetal Rhc examination in plasma of pregnant women with anti‐c

Anti-Rhc antibodies may be the reason for the hemolytic disease of the newborn, therefore, noninvasive Rhc determination is important for pregnancy monitoring. For this purpose, we decided to introduce real-time polymerase chain reaction (PCR) method. Blood from 200 donors, plasma and whole-blood from 11 Rhc-negative mothers, as well as blood from fathers and newborns were examined. Rhc sensitivity and specificity were first determined by real-time PCR using genomic DNA from donors. The same Rhc genotyping method was used for fetal Rhc detection in maternal plasma. To confirm the fetal Rhc-negative result, plasma was tested with a panel of biallelic insertion/deletion polymorphisms for the presence of fetal DNA. The c allele assay showed full specificity. The mean Ct value for one copy of c allele diluted in C-negative DNA was determined from extrapolating the correlation curve as 39.9. Full concordance was observed between the fetal Rhc genotypes from maternal plasma and the newborn phenotypes. Preliminary results show that it is possible to examine fetal c allele of RHCE gene in the plasma of pregnant women with anti-c by means of a noninvasive method. The diagnostic accuracy of the procedure, however, has yet to be confirmed in a larger group.

The Structure and Function of the Rh Antigen Complex

The Rh system is one of the most important and complex blood group systems because of the large number of antigens and the serious complications for the fetus of a woman sensitized by transfusion or pregnancy. Major advances in our understanding of the Rh system have occurred with the cloning of the genes and with functional evidence that the Rh blood group proteins belong to an ancient family of membrane proteins involved in ammonia transport. The arrangement and configuration of the genes at the RH locus promotes genetic exchange, generating new antigens. Importantly, RH genetic testing can now be applied to clinical transfusion medicine and prenatal practice. This includes testing for RHD zygosity, confirmation or resolution of D antigen status, and detection of altered RHD and RHCE genes in individuals at risk for producing antibodies to high-incidence Rh antigens, particularly sickle cell disease (SCD) patients. The Rh proteins form a core complex that is critical to the structure of the erythrocyte membrane, and they may play a physiologic role in the sequestration of blood ammonia. The Rh family of proteins now includes non-erythroid homologs present in many other tissues, and comparative genomics reveal Rh homologs in all domains of life.

Molecular determination of RHD zygosity

Determining the RhD zygosity of a partner is valuable for the management of hemolytic disease of the newborn (HDN) related to anti-D. Zygosity is typically predicted using Rh phenotype. However, this may not be satisfactory in all ethnic groups. Our goal was to develop a robust clinical assay for RhD zygosity using molecular techniques that is suitable for use in both Caucasian and African-American populations. We used quantitative fluorescent PCR to detect RhD exons 5 and 7 with an internal control, exon 7 from the RhCE gene. PCR products were quantified by an automated sequencer. The ratio of exon 5 or 7 amplicon to the internal control determined RhD copy number. Accuracy was assessed using 17 Caucasian and 11 African-American samples whose zygosity was predicted from an Rh phenotype and 11 HDN paternal samples predicted heterozygous after the fetus tested RhD-negative. The assay accurately distinguished the 2 genotypes. Ratios for the DD and Dd genotypes for exon 5 and exon 7 were distinct and non-overlapping (Table). Common variant alleles such as DVI and the RhD pseudogene are recognized when the RhD copy number of exon 5 and exon 7 are discordant. All 17 Caucasian samples were concordant with serology. We found 2 discrepancies out of 11 African-American samples; however, the serology prediction for both cases was only 50-58%. All results were concordant for the 11 HDN paternal heterozygous samples. This molecular assay accurately assesses RhD zygosity and helps predict the risk that a fetus will inherit RhD.Tabled 1Exon Ratios Determine RhD Copy NumberExon 5Exon 5Exon 5Exon 7Exon 7Exon 7Copy#MeanRange3SDMeanRange3SDDD1.051.00-1.120.091.271.07-1.430.30Dd0.530.45-0.570.090.680.55-0.770.18 Open table in a new tab

Fetal Blood Group Genotyping

Prediction of fetal blood group from DNA is usually performed when the mother has antibodies to RhD, to assess whether the fetus is at risk from hemolytic disease of the fetus and newborn (HDFN). Over the last five years RhD testing on fetal DNA in maternal plasma has been introduced. At the International Blood Group Reference Laboratory (IBGRL) we employ real-time quantitative polymerase chain reaction (RQ-PCR) to detect RHD exons 4, 5, and 10, which also reveals RHDpsi. SRY and, in RhD-negative (RhD-) females, eight biallelic polymorphisms are incorporated in an attempt to provide an internal positive control. Since 2000 we have tested 533 pregnancies for RhD. In 327 pregnancies where the RhD of the infant is known, we had one false-positive and one false-negative result. In 2004 we introduced fetal typing from DNA in maternal plasma for K, Rhc, and RhE, which represent single nucleotide polymorphisms (SNPs) on the KEL and RHCE genes. We have begun trials on an automated method for fetal RhD typing from DNA in maternal plasma. This is designed to test fetal RhD in all pregnant RhD- women, to identify the 40% with an RhD- fetus so that antenatal RhD immunoglobulin (Ig) prophylaxis can be avoided. Similar trials have already been reported by Sanquin Research Laboratories in Amsterdam.

Stratégie d'identification des variants du gène RHCE au Centre national de référence pour les groupes sanguins : impact sur la sécurité transfusionnelle

The RH blood group is the most polymorphic and immunogenic blood group system. The RH locus is composed of 2 highly homologous genes: the RHD gene encoding the D polypeptide; and the RHCE gene, encoding C or c together with either E or e polypeptides. Numerous variants exist for both RHD and RHCE genes. Among them we were interested in the serological and molecular definition of numerous pre-published RHCE variants encountered in different populations. The identification of these variants is crucial to ensure the transfusion safety for patients expressing these variants. Here we propose a procedure to identify some of them and discuss the adequate transfusion strategy. This procedure has enable us to identify new variants to be presented at the symposium.

Molecular genetics of RH and its clinical application : Génétique moléculaire sur système RH et ses applications cliniques

Background The RH genes RHD and RHCE encode two proteins that represent the clinically most important blood group system defined by the sequences of red cell membrane proteins. In the last five years the field has been moving from defining the underlying molecular genetics to applying the molecular genetics in clinical practice. Materials and methods The state of the current knowledge is briefly summarized using recent reviews and original work since 2000. Results The RHD and RHCE genes are strongly homologous and located closely adjacent at the human chromosomal position 1p36.11. Part of the genetic complexity is explained by the clustered orientation of both genes with their tail ends facing each other. The SMP1 gene is located interspersed between both RH genes. Using additional genetic features of the RH gene locus, RHCE was shown to represent the ancestral RH position, while RHD is the duplicated gene. More than 150 alleles have been defined for RHD alone. They were classified based on antigenic and clinical properties into phenotypes like partial D, weak D and DEL. Among the D negative phenotype a large variety of non-functional alleles were found. The frequencies of these distinct alleles vary widely among human populations, which has consequences for clinical practice. Conclusion Rhesus is a model system for the correlation of genotype and phenotype, facilitating the understanding of underlying genetic mechanisms in clustered genes. With regard to clinical practice, the genetic diagnostics of blood group antigens will advance the cost-effective development of transfusion medicine.

The genetic basis of hair whorl, handedness, and other phenotypes

Evidence is presented that RHD, RHCE, and other RH genes, may be interesting candidates to consider when searching for the genetic basis of hair whorl rotation (i.e., clockwise or counterclockwise), handedness (i.e., right handed, left handed or ambidextrous), speech laterality (i.e., right brained or left brained), speech dyslexia (e.g., stuttering), sexual orientation (i.e., heterosexual, homosexual, bisexual, or transsexual), schizophrenia, bipolar disorder, and autism spectrum disorder. Such evidence involves the need for a genetic model that includes maternal immunization to explain some of the empirical results reported in the literature. The complex polymorphisms present among the maternally immunizing RH genes can then be used to explain other empirical results. Easily tested hypotheses are suggested, based upon genotypic (but not phenotypic) frequencies of the RH genes. In particular, homozygous dominant individuals are expected to be less common or lacking entirely among the alternative phenotypes. If it is proven that RH genes are involved in brain architecture, it will have a profound effect upon our understanding of the development and organization of the asymmetrical vertebrate brain and may eventually lead to a better understanding of the developmental processes which occur to produce the various alternative phenotypes discussed here. In addition, if RH genes are shown to be involved in the production of these phenotypes, then the evolutionary studies can be performed to demonstrate the beneficial effect of the recessive alleles of RHD and RHCE, and why human evolution appears to be selecting for the recessive alleles even though an increase in the frequency of such alleles may imply lower average fecundity among some individuals possessing them.

Rh proteins: Key structural and functional components of the red cell membrane

Rh (Rhesus) proteins (D, CcEe) are expressed in red cells (RBC) in association with other membrane proteins (RhAG, LW, CD47 and GPB). By interacting with the spectrin-based skeleton through protein 4.2 and ankyrin, the Rh complex contributes to the maintenance of the mechanical properties of the erythrocyte membrane. The RH system is one of the most immunogenic and polymorphic human blood group system. Molecular basis of most Rh phenotypes, including the Rh null phenotype associated with hemolytic anemia, have been determined. The demonstration that the RHD -positive locus is composed of the RHD and RHCE genes, whereas the RHD gene is deleted in most RhD-negative individuals, allowed fetal RhD genotyping by non-invasive PCR assays for antenatal diagnosis of pregnancy at risk for Rh hemolytic disease of the newborn. In mammals, the Rh protein family includes two non-erythroid members, RhBG and RhCG, mainly expressed in liver and kidney, two organs specialized in ammonia genesis and excretion. Functional analyses in heterologous systems revealed that RhAG, RhBG and RhCG can mediate ammonium (NH 3 and/or NH 4 + ) transport across the cell membrane and might represent mammalian specific ammonium transporters. Furthermore, recent studies performed in human and murine red blood cells (RBC) indicate that RhAG facilitates CH 3NH 2/NH 3 movement across the membrane and represents a potential example of gas channel. The crystallographic structure of the bacterial ammonia channel AmtB and functional studies showing that AmtB conducts NH 3 into reconstituted vesicles is fully consistent with these latter studies. In RBCs , RhAG may transport NH 3 to detoxifying organs like kidney and liver and with non-erythroid tissues orthologs may contribute to regulation of the acid-base balance.

Molecular basis of the JAHK (RH53) antigen

The JAHK antigen was first described in 1995 as a low-frequency red blood cell antigen. Family studies confirmed the association of the antigen with the rare r(G) phenotype of the Rh blood group system, which is associated with weak expression of C and e, but normal G expression. JAHK was allocated the Rh number RH53. The serologic findings indicated the location of the antigen on the RhCE protein, although the molecular basis for JAHK has not been known. The RHCE gene of eight persons from three unrelated families was analyzed by exon amplification and direct sequencing. Four of the samples were JAHK+ the remaining four were JAHK-. In one JAHK+ sample, the entire RHCE gene was sequenced. The remaining samples were sequenced for exons 1 to 3. A polymerase chain reaction procedure with sequence specific primers was developed for the specific detection of the JAHK allele. Analysis of the entire RHCE gene of one JAHK+ sample showed the expected CcEe-specific nucleotide sequences and revealed an additional nucleotide change (365C>T) in exon 3. This change represented a missense mutation, which led to an amino acid substitution from serine to leucine at position 122 of the RhCE protein. Three JAHK+ samples from two other unrelated families showed the 365C>T mutation and confirmed the association of the Ser122Leu substitution with the JAHK+ phenotype. The molecular basis of the JAHK antigen (RH53) is defined by a 365C>T mutation in exon 3 of the RHCE gene leading to the amino acid substitution Ser122Leu. Because the position 122 is predicted to be located in the transmembrane region adjacent to the second loop, the substitution of the neutral serine by the hydrophobic leucine seems to be the cause of the JAHK antigen by a conformational change of the RhCE protein. This structural change may also cause the weakened expression of the C and e antigens observed in JAHK+ individuals. Based on our results it is concluded that the JAHK-specific mutation is associated with a dCe haplotype.

Non-invasive Fetal RHD and RHCE Genotyping Using Real-time PCR Testing of Maternal Plasma in RhD-negative Pregnancies

We assessed the feasibility of fetal RHD and RHCE genotyping by analysis of DNA extracted from plasma samples of RhD-negative pregnant women using real-time PCR and primers and probes targeted toward RHD and RHCE genes. We analyzed 45 pregnant women in the 11th to 40th weeks of pregnancy and correlated the results with serological analysis of cord blood after delivery. Non-invasive prenatal fetal RHD exon 7, RHD exon 10, RHCE exon 2 (C allele), and RHCE exon 5 (E allele) genotyping analysis of maternal plasma samples was correctly performed in 45 out of 45 RhD-negative pregnant women delivering 24 RhD-, 17 RhC-, and 7 RhE-positive newborns. Detection of fetal RHD and the C and E alleles of RHCE gene from maternal plasma is highly accurate and enables implementation into clinical routine. We recommend performing fetal RHD and RHCE genotyping together with fetal sex determination in alloimmunized D-negative pregnancies at risk of hemolytic disease of the newborn. In case of D-negative fetus, amplification of another paternally inherited allele (SRY and/or RhC and/or RhE positivity) proves the presence of fetal DNA in maternal circulation.

Non-invasive fetal RHD and RHCE genotyping from maternal plasma in alloimmunized pregnancies

In this prospective study, we assessed the feasibility of fetal RH genotyping by analysis of DNA extracted from maternal plasma samples of alloimmunized pregnant women using real-time PCR and primers and probes targeted toward RHD (exon 7 and exon 10) and RHCE (intron 2 and exon 5) genes. We analysed 23 alloimmunized pregnant women (16 anti-D, 5 anti-D + C, 2 anti-E) at risk of haemolytic disease of the newborn (HDN) within 11th and 37th week of pregnancy and correlated the results with serological analysis of cord blood. Detection of the presence of the RHD gene, the C and/or E alleles of the RHCE gene in maternal plasma samples is highly accurate and enables implementation in a clinical diagnostic algorithm for following pregnancies at risk for HDN. The absence of RHD gene, the C and/or E alleles of RHCE gene in the current pregnancy excludes the risk of HDN caused by anti-D, anti-C and/or anti-E alloantibodies and the performance of invasive fetal-blood sampling.

Rhnull Syndrome: Identification of a Novel Mutation in RHce Gene.

Background: Rhnull syndrome, which includes the amorph and regulator types, is a rare genetic disorder characterized by stomatocytosis and chronic mild hemolytic anemia. The suppression of Rh antigen expression for regulator types is attributed to mutations of the RHAG gene. The deficiency of Rh proteins on the red blood cells (RBCs) from the rare individuals of the Rhnull amorph type may be the result of homozygosity for a silent RHCE allele at the RH locus in which the RHD is absent. We studied a Brazilian family transmitting an amorph Rhnull disease gene on a consanguineous background and identified a novel mutation in RHce gene causing the loss of function phenotype.Methods: RBCs from two Rhnull sisters (G1 and G2) of the amorph type and from family members were analyzed by serology and flow cytometry with monoclonal antibodies specific for Rh (D, C, c, E and e), and LW antigens, for RhAG and CD47 as well as alloantibodies directed against GPB (S, s and U) antigens. Genomic DNA samples and transcripts were tested by PCR and sequence analysis.Results: RBCs from G1 and G2 did not react with the anti-Rh and anti-LW reagents and reacted weakly with anti-RhAG, anti-CD47, anti-s, and anti-U reagents. RBCs from G1 were S+ and from G2 S-. Molecular analyses showed a deletion of the nucleotide at position 963 in exon 7 of the RHce gene [GGG(Glu321→GG)] in addition to a deletion of the RHD gene. This nucleotide deletion in exon 7 introduced a frameshift after Glu321 and a premature stop codon, resulting in a shorter predicted protein with 359 amino acids, including a new C-terminal sequence that is likely to alter the protein conformation and impair the Rh complex assembly.Conclusion: We describe a novel mutation of an amorph Rhnull disease gene leading to a loss of function phenotype. Our findings reinforce previous studies suggesting that protein folding and/or protein-protein interaction mediated by the C-terminal domain of the Rh proteins plays a role in the stability of the Rh membrane complex.

A new hybrid RHCE gene (CeNR) is responsible for expression of a novel antigen.

The red blood cells (RBCs) of a patient, known to have the probable DC(W)(e)/D-- phenotype, typed as D(W)- and Rh32- but were unexpectedly agglutinated by an anti-D(W)/Rh32 serum. The reactivity suggested that the RBCs carried a novel antigen and that the molecular background of this DC(W)(e)/D-- phenotype might be different from those reported. The purpose of this study was to determine the molecular basis of the Rh phenotype. Samples were obtained for family studies. Standard hemagglutination methods were used. RH mRNA transcripts were isolated by reverse transcription-polymerase chain reaction and sequenced. Sequence analysis revealed that the probond had three different RH transcripts: a normal RHD and two different hybrid transcripts from the RHCE locus, a RHCE-D hybrid with exon 1 from RHCE associated with the D-- haplotype, and a new RHCE-D hybrid. In this new hybrid, exons 1 to 5 are RHCe-specific and exons 6 to 10 correspond to RHD. The C(W) antigen is also encoded by this hybrid gene. Family studies confirmed that the new RHCE-D hybrid is linked in cis to conventional RHD. A new RHCE-D structure is associated with altered expression of C and e antigens in this family and the generation of a novel low-prevalence antigen (CENR).

RH locus contraction in a novel Dc-/D-- genotype resulting from separate genetic recombination events.

The rare phenotypes Dc- and D-- lack the expression of E/e and CcEe antigens, respectively; their cotransmission in a single family has not been reported. Six members of a Chinese family with two exhibiting the Dc- phenotype were studied using standard serologic methods. Rh genotypes were analyzed by Southern blot, and RH loci, by exon PCR. Rh transcripts were characterized by gene-specific RT-PCR and sequencing. Although Rh typing detected two members as Dc- homozygotes, RFLP analysis and exon PCR showed them to be Dc- heterozygotes with a partial deletion of RHCE. cDNA sequencing showed the expression in the family of normal RHD and RHCe as well as hybrid transcripts, RHD(1-9)/RHCE(10) and RHCE(1-3)/RHD(4-10). Thus, the Dc- members had the genotype of Dc-/ D-- and expressed both hybrid genes that were inherited from their parents, respectively. This is the first demonstration in a family that the Dc- and D-- complexes neither are linked with a normal RHD or RHCE gene. The segregation of these two different hybrid genes with single break points suggests their independent genetic origin and provides molecular insights into the dynamic nature of genomic rearrangements leading to RH locus contraction.

Deletion of arginine codon 229 in the Rhce gene alters e and f but not c antigen expression.

Rh CcEe antigens occur as ce, Ce, cE, or CE alleles in the RBC membrane. Their epitope structures and the location of their cis interacting products remain to be defined. A rare blood sample from a white male whose parents are first cousins was identified. Hemagglutination was performed using standard methods. RH structure and genotype was assessed by Southern blots. Rh transcripts were obtained by gene-specific RT-PCR and sequenced. The mutation was verified by genomic PCR assays. The donor's RBCs typed D+C-c+E-e-f(Rh6)- with a normal c dose, suggesting the Dc- phenotype. Further tests revealed a weak and qualitatively altered e expression. Southern blots indicated a genotype of Dce/dce without other gross changes. RT-PCR detected a triplet deletion (Delta685AGA687) in the Rhce gene that specifies codon 229 for arginine (Arg229). Sequencing of the region around the mutated exon 5 confirmed the donor to be homozygous for the AGA deletion. Arg229 is invariant on external loop 4 and close to the Ala226Pro change specific for e/E polymorphism. The qualitative and quantitative alteration of e antigen defines Arg229 as a crucial component for e/E epitope presentation. Given a normal dose of c antigen, the disruption of f (Rh6) by Arg229 deletion suggests that external loop 4 is a major structural element contributing to the expression of RHCE cis interacting antigenic products.