Analysis of RHD alleles in Argentineans with variant D phenotypes

LUJÁN M; TRUCCO BOGGIONE C; RACCA A; TARRAGO M; NOGUES N; MUÑIZ DIAZ E; COTORRUELO C

Lisboa

Congreso; XXI Regional Congress. International Society of Blood Transfusion; 2011

International Society of Blood Transfusion

Background: The serologic assignment of the RhD status may be hindered in patients with a weak expression of the D antigen hampering clinical decision making in transfusion and obstetric medicine. Partial D and weak D types show substantial ethnic variability. Some alleles are confined to specific ethnic groups whereas others are more dispersed. A comprehensive study of RHD alleles occurring in the mixed population of Argentina is necessary to evaluate the most suitable DNA typing strategy. Aims: The aim of this study was to characterize the molecular background of samples with weak D antigen expression in two stratified groups of the population of Rosario, the third largest city located in the central area of Argentina. Materials and Methods: Two sample cohorts of unrelated adults were studied. The first group (G1) included 12672 random samples collected at a public health care center and the second group (G2) included 5707 samples collected at a private clinical laboratory. Each group represents different social strata of the population. The Rh phenotype was performed by hemagglutination using specific monoclonal antibodies. DNA samples with weak D antigen expression were initially screened using PCR SSP methods to detect weak D types 1, 2, 3 and 4 alleles. Variant samples not classified were further studied by RHD exon scanning, PCR SSP for DVII or sequencing. Results: The frequency of D positive, D negative and variant D phenotypes differed significantly (p<0.001) between G1 and G2 (94.49% vs 87.66%, 5.15% vs 11.58%, 0.36% vs 0.75%, respectively). Eleven different alleles were responsible for the weak D expression. Even though the frequency of samples with weak D antigen expression in G1 was significantly lower than in G2, the distribution of the variant D phenotypes responsible for the weak serological reaction encountered in each group did not differ significantly (p=0.18, Fisher’s exact test). Approximately 60% of the weakly reacting samples from G1 and G2 were weak D types 1 through 4.0 and 25% were D category VII. RHD alleles associated with African ancestry (weak D type 4.2, DIVa, DAU-4 and DOL) were only encountered in G1 and the weak D type 4.0 phenotype was more frequently found in G2. A new G>A mutation at the D specific position -282 within the promoter region of DAU-4 and DOL alleles was also identified. It was estimated that approximately 1 out of 29 individuals that today are considered D negative for transfusion or pregnancy could in fact be managed as D positive. Conclusions: The D phenotype distribution found in G2 resembles that in Europeans while the frequencies in G1 may account for the Amerindian and African genetic contribution. The genotyping strategy used in this work is suitable to study the variant D phenotypes that are present in the overall population and will allow a better use of the few available D negative units and a more rationale administration of anti-D immunoglobulin.