Objective: To delineate the blood group for a pair of twins with inconclusive ABO blood typing result.
Methods: Serological test for blood group was carried out by using ABO and Rh Blood Grouping Cards (Microcolumn Gel Immunoassay). Sequence specific primer-PCR (PCR-SSP), direct sequencing and TA clone sequencing were used to analyze the ABO gene. Genetic status was analyzed by using 16 short tandem repeat (STR) markers.
Results: Red blood cells of the twins displayed 2+ mixed agglutination phenomenon with anti-A, anti-A1 and anti-E. PCR-SSP and DNA sequencing of exons 6 to 7 revealed that they have an ABO*O.01.01/ABO*O.01.02 genotype. DNA sequencing of microsatellite enhancer region revealed presence of A gene. STR analysis revealed more than two haplotypes for 9 loci between the twins. After clustered by anti-A, the red blood cells were divided into two groups: A, CcDEe and O, CcDee, respectively.
Conclusion: Serological and molecular techniques have characterized the twins as blood group chimeras.