A family study of the Chinese Rhnull individual of the regulator type: a novel single missense mutation identified in RHAG gene

A novel frameshift mutation in RHAG leads to Rhnull phenotype in a Chinese individual

BACKGROUND

We recently encountered a Rhnull phenotype proband within one family in the Chinese population. Rhnull is a rare autosomal recessive disorder characterized by the absence of the Rh antigens on the erythrocyte membrane, resulting in chronic hemolytic anemia. This study described the serological and molecular analysis of a Chinese Rhnull proband and his immediate family.

METHODS

Red blood cells antigen phenotyping and antibody screening/identification were conducted. RHD, RHCE, and RHAG were analyzed using genomic DNA by polymerase chain reaction and sequence analysis.

RESULTS

Serologic tests showed a D-C-E-c-e- phenotype in the proband associated with the suspicion of anti-Rh29 (titer 16). Molecular analyses showed a new mutation (c.406dupA) in exon 3 of RHAG. This duplication introduced a reading frameshift (p.Thr136AsnfsTer21). The RHAG mutation was found in the homozygous state for the proband and heterozygous state for his parents.

CONCLUSION

We identified a novel RHAG mutation resulting in the Rhnull phenotype of the regulator type. Inheritance of the novel allele was shown by family study.

Molecular and serological analysis of the D variant in the Chinese population and identification of seven novel RHD alleles

BACKGROUND

The molecular basis of the D variant phenotype in the Chinese differs greatly from that of the Caucasian. Adapting a specific D typing strategy to the spectrum of prevalent RHD variant alleles is necessary.

STUDY DESIGN AND METHODS

Blood samples with ambiguous D phenotypes were collected in the Southern Chinese population. A special three-step typing strategy was applied. First, the common DVI type 3 was identified from epitope profiles of D antigen. Then, another common weak D type 15 (RHD*845A) was identified by epitope profiles of D antigen and Sanger sequencing of RHD exon 6. Finally, the remaining D variants were genotyped mainly by Sanger sequencing. For the novel RHD alleles in the coding region and exon-intron junction, in vitro transfection and minigene splicing assays were performed, respectively. The anti-D investigation was performed.

RESULTS

DVI type 3 (65/253, 25.7%) and weak D type 15 (62/253, 24.5%) were common Chinese D variants, and RHD*960A, DFR, RHD*weak D type 25, 72, and 136 were frequent variant RHD alleles. Besides, twenty-two sporadic and seven novel RHD alleles (RHD*188A; RHD*688C; RHD*782 T; RHD*1181C; RHD*165 T, 993A; RHD*148 + 3G > T and RHD*1227 + 5G > C) were identified. The deleterious effect of the novel RHD alleles on D antigen or mRNA expression was confirmed. Anti-D was detected in two DVI type 3 pregnant women.

DISCUSSION

The three-step typing strategy provides an effective approach for Chinese D variant typing. It can be anticipated that commercially available RHD genotyping kits have limitations for testing Chinese D variants, as some of the frequent variants are not interrogated.

Correlation among automated scores of agglutination, antigen density by flow cytometry and genetics of D variants

BACKGROUND

Laboratory testing to identify the molecular basis of serologic weak D phenotypes is recommended to determine whether a pregnant woman or potential transfusion recipient should be managed as RhD-positive or RhD-negative. The variation in D antigen expression on RBCs, different potencies of anti-D typing reagents, lack of standardized test methods, and the subjectivity of interpreting agglutination reactions complicate the detection of D variants. We evaluated the correlation of agglutination scores by an automated immunoassay analyzer with D antigen densities determined by flow cytometry, and D variant types identified by molecular analysis.

MATERIALS AND METHODS

We selected 273 blood donor samples with agglutination scores of less than 92 (4+), measured by an automated analyzer (NEO®, Immucor, Norcross, GA, USA). D antigen densities were measured by flow cytometry for 89 samples. Samples were classified as molecularly-determined weak D or partial D variants by multiplex PCR, PCR RFLP and DNA sequencing.

RESULTS

All samples with a D antigen density ≥15% had an agglutination score >80 (4+). Agglutination scores for weak D types varied from 10 to 90. Agglutination scores for partial D antigens were graded with scores varying from 60 to 99. D antigen densities varied from 0.55% to 10.67% for weak Ds and 4.1% to 30.5% for partial Ds.

DISCUSSION

Our results showed that score values follow a pattern among D variants that could be related to antigen density and to the RhD variant classification.

A RHAG point mutation selectively disrupts Rh antigen expression

OBJECTIVES

The aim of this study was to characterise a novel mutation in the gene encoding RhAG in order to elucidate a molecular mechanism for Rh antigen expression and spherocytosis.

BACKGROUND

Rhesus-associated glycoprotein (RhAG) is critical for maintaining the structure and stability of erythrocytes. Single missense mutations in the gene encoding RhAG are sufficient to induce spherocytosis and deficiencies in Rh complex formation. We report a novel missense mutation that incompletely disrupts Rh antigen expression and selectively knocks out RhD antigen expression.

METHODS

Blood samples were taken from a 38-year-old male, his brother, his wife and his daughter in Xi'an, China. To detect the proband's RhAG and D antigen expression, the RBC were stained with anti-D and anti-RhAG and analysed by flow cytometry. Red blood cell morphology was detected with atomic force microscopy (AFM). Genomic DNA was isolated from whole blood samples, and the RHD, RHCE and RHAG alleles were sequenced and analysed. The mutation was mapped onto a predicted crystal structure of RhAG by the I-TASSER server and visualised using PyMOL.

RESULTS

Morphological testing by AFM found clear evidence of spherocytosis in the proband's erythrocytes. RHAG gene sequencing identified the mutation at sequence 236G > A, resulting in a serine to asparagine substitution at residue 79 (S79N). Family survey indicated that inheriting this allele is necessary and sufficient to cause the condition. Mapping the mutation onto a predicted crystal structure of RhAG revealed the proximity of the mutation to the critical structural elements of the protein.

CONCLUSIONS

A novel RHAG mutation significantly lowers RhAG antigen expression and antigen-mediated agglutination intensity.

Novel RHAG allele encoding the Rh(null) phenotype in Brazil

Rhnull is a rare phenotype characterized by the loss of Rh antigen expression. This phenotype can be related to several molecular backgrounds. In this study, we show a novel allele in a Brazilian pregnant woman encoding the Rhnull phenotype due to a change in RHAG exon2 c.310C>T, which leads to a premature stop codon (Gln104Stop).