Sequencing analysis showed more allelic combinations in nonpygmoids than in pygmoids with high frequencies of DO*HY, DO*JO, and DO*B-SH-Gln149Lys variant alleles. This finding underlines the importance of including DO*HY and DO*JO single-nucleotide polymorphisms in genotyping tests to improve transfusion safety. Characterization of two novel DO*B alleles highlights the value of testing selected ethnic groups in understanding DO allele diversity.

Summary To gain further insight into ART4 (DO) gene alleles (DO*A, DO*JO1, DO*A‐WL, DO*DOYA, DO*B, DO*B‐WL, DO*B‐SH‐Q149K, DO*B‐(WL)‐I175N, DO*HY1, DO*HY2, DO*DOMR) and evaluate the impact of synonymous nucleotide polymorphisms on protein expression and mRNA accumulation of DO*A‐HA, DO*A‐SH and DO*B‐SH alleles, human erythroleukaemic K562 cells were transducted with variant DO‐lentiviral particles and analysed by flow cytometry and quantitative reverse transcription polymerase chain reaction. Monoclonal antibody (MoAb) detection of DO*A‐HA and DO*JO1 transductants was lower than DO*A transductants, while detection of DO*A‐SH, DO*A‐WL and DO*DOYA transductants was higher. Variant DO*B alleles, i.e. DO*B‐SH, DO*B‐WL, DO*HY1, DO*HY2 and DO*DOMR, showed reduced MoAb binding. The unexpected modifications of protein expression of the DO*A‐HA, DO*A‐SH and DO*B‐SH alleles that differ from the DO*A or DO*B alleles by a single synonymous polymorphism were abolished by reversion, thus implying involvement of these polymorphisms. Depending on the Leu208 codon used, detection level ranged from 1 to 4·14. In the variant alleles resulting from single synonymous polymorphism, mRNA accumulation correlated roughly with MoAbs detection levels, suggesting post‐transcriptional regulation. Other than a few reports involving aberrant splicing, the experiments described herein provide the first evidence that synonymous nucleotide polymorphisms can influence Dombrock blood group expression. Such polymorphisms should be taken into account for molecular screening and potential impact on transfusion.

BACKGROUND Due to the unavailability of immunological reagents, the Dombrock blood group is insufficiently explored in African populations and can be a source of alloimmunization. A large study including pygmoid and nonpygmoid ethnic groups from East, Central, and West continental Africa, together with African migrants like Comorians, Afro‐Caribbean from Martinique, and Maroons from French Guiana would be helpful to increase transfusion safety. STUDY DESIGN AND METHODS Using genomic DNA extracted from blood samples collected from 336 nonpygmoid and 51 pygmoid Africans as well as 268 samples of African descent, DO coding regions were PCR‐amplified and sequenced. RESULTS DO*A and DO*B alleles were detected in almost all groups, with a clear predominance of DO*B in every cohort tested. DO*JO and DO*HY allele frequencies reached 10% or more in several ethnic groups. DO*B‐SH‐Gln149Lys, DO*B‐Ile5Thr, and DO*DODE variants were identified both in African ethnic groups and outside Africa. Twelve novel variants were characterized on a DO*A or a DO*B background. Five of them were found in both African and migrant cohorts, the others were restricted to either within or outside Africa. No DO*DOYA, DO*DOLG, DO*DOLC, nor DO*DOMR variants were observed. A first phylogenetic tree was proposed including all variant alleles. CONCLUSION This study across continental Africa and countries with African migrants provides a useful overview of Dombrock allele diversity and distribution. The identification of 12 new alleles underlines the importance of genotyping for Dombrock alleles, particularly to improve transfusion safety in countries hosting migrant populations of African descent.

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