Background/Case Studies: A 21-year-old individual of Egyptian ancestry with a history of microcytic anemia due to iron deficiency demonstrated an ABO typing discrepancy due to a possible rare subtype. Serological, lectin, and genotype tests were performed to investigate the blood type.
Study
Design/Methods: Serological testing was performed to determine the red blood cell (RBC) phenotype, and ABO subtyping was performed using commercial anti-A1 (Dolichos biflorus) lectin. Sanger sequencing (SS) of the ABO promoter, enhancer, exons 1-7, and flanking intron regions was performed to investigate the ABO alleles. Targeted next generation sequencing (NGS) was performed to determine the additional blood group alleles.
Results/Findings: Serological investigation revealed the typing discrepancy to be caused by the A2B subtype with unexpected anti-A1 antibodies. SS inferred the ABO genotype to be ABO*A2.01 / B.01, consistent with the results of serological typing. The RBCs were strongly reactive with anti-A, anti-B, and anti-A,B reagents. However, they also demonstrated unexpectedly moderate reactivity with anti-A1 lectin. It has been found that some A2 cells demonstrate weak variable reactivity with commercial anti-A1 reagents. The results of genotype testing are summarized in Table 1. Conclusions: The AB blood type within the Egyptian population has been reported to be 9.74%, and 91.78% are Rh positive. However, the prevalence of the A2.01 allele and the expression of the partial c antigen within this population are currently unknown. The percentage of A2B individuals who form anti-A1 antibodies has been estimated to be 22-35%. Because there is no previous history of pregnancy or transfusion, the anti-A1 antibody was most likely naturally stimulated. Partial c antigen expression is associated with a higher risk of alloimmunization. The FY*02N.01 allele (GATA-1 silencing mutation) impairs promoter activity in erythroid cells, preventing Fyb antigen expression on RBCs but not on other tissues; therefore, anti-Fyb antibodies are uncommonly formed by these individuals. While the erythroid silent Fy(a-b-) phenotype is prevalent in nearly 100% of West African ancestry, the prevalence of this within the Egyptian population is currently unknown. Aside from ABO and Rh, blood group allelic frequencies within the Egyptian population are understudied.
