The Duffy-null phenotype in Saudi Arabia: distribution, origins and clinical significance

Background The Duffy antigens Fy a and Fy b , encoded by ACKR1 (formerly DARC ), are absent from red cells in the Fy(a−b−) phenotype, which almost always arises from homozygosity for the FY *02N.01 GATA-box variant (rs2814778). It bears on two everyday problems in non-malignant hematology, red-cell alloimmunization and the interpretation of a low neutrophil count, and confers protection against Plasmodium vivax . Arabian data have been phenotypic and sparse. Objective To assemble the Saudi and Gulf evidence on Duffy-null frequency and follow it into transfusion support, neutrophil reference intervals and vivax surveillance. Methods PubMed and Web of Science were searched from July to September 2026, pairing Duffy, ACKR1 , DARC and rs2814778 with Arabian regional terms, neutropenia, reference intervals and alloimmunization. Confidence intervals are Wilson intervals recomputed from reported counts. Results Provincial Fy(a−b−) frequency ranges from 26.7% in the north to 78.3% in Jazan, with Oman (68.5%) nearest and lower figures in the lower Gulf, consistent with enriched African ancestry at ACKR1 . In male Jazan donors the Duffy-null neutrophil interval was 1,140–5,290/µL and institutional limits classified 50.9% as neutropenic; isolated neutropenia reaches 21% locally. Duffy alloimmunization is documented at every Saudi center examined, exclusively as anti-Fy a , though the rates are not directly comparable. Conclusion Jazan carries among the highest Duffy-null frequencies reported outside sub-Saharan Africa, with direct consequences for transfusion support and for neutrophil reference intervals. One western Saudi cohort has been genotyped at the FY promoter; the southwest, where frequencies are highest, has not, and closing that gap is the most tractable next step.