An analysis of more than 500,000 blood samples discovered a rare mutation that causes type B blood enzymes to have similar activity to those in type A.
A team of scientists in Thailand has identified an extraordinarily rare blood mutation that may help explain why blood sometimes behaves unpredictably during medical examinations.
The discovery, reported in a publication in the journal Transfusion and Apheresis Science, emerged from an eight-year review of more than 544 thousand blood samples at Siriraj Hospital in Bangkok.
Led by hematologist Janejira Kittivorapart of Mahidol University, researchers were investigating the causes of ABO discrepancies, which refer to cases in which a patient’s red blood cells and blood plasma have conflicting test results of blood typing. These discrepancies can delay transfusions and complicate treatment.
Of the 544,230 samples examined, only 396 patient samples (0.15%) showed discrepancies. After excluding cases related to stem cell transplants, researchers analyzed 198 samples from patients with unexplained results. Among them, they identified an individual with an extremely rare variation of blood type B, known as the B(A) phenotype. Two additional cases were found among 285,450 donor samples, meaning that just three examples appeared throughout the data set.
The B(A) phenotype occurs when type B blood presents genetic mutations that give its enzymes an activity similar to that of type A. This causes standard blood typing tests to produce contradictory results, confusing laboratory analyses. It is estimated that the variation occurs in approximately 0.00055% of people (about one in every 180 thousand) and had never been documented in this genetic form, explains .
Additional investigations revealed four previously unreported mutations in the ABO gene, which controls the enzymes that add specific sugars to red blood cells to create blood group antigens. Although individuals technically have type B blood, the mutated enzyme produces traces of the A antigen, triggering the observed discrepancies.
The findings highlight how even the most widely used blood typing systems can not detecting subtle genetic variations. According to the researchers, more studies are needed to determine how the mutant enzyme works and how it changes the structure of the antigen.
The discovery adds to a growing list of rare blood types identified in recent years. In 2024, researchers finally uncovered one involving an unusual blood sample from a pregnant woman, collected in 1972, confirming that it belonged to a completely new blood group system. Earlier this year, French scientists reported another unprecedented discovery: , found in a single woman.
