BACKGROUND: In addition to the common ABO phenotypes, numerous phenotypes with a weak expression of the A or B antigens on red blood cells have been found. DNA genotyping on A3 e A3B subgroups has been performed in small number of samples, mainly in family studies. To date, seven ABO alleles have been associated to A3 and A3B subgroups (ABO*A301 to ABO*A307) revealing molecular heterogeneity. Our purpose was to study molecular events on exon 7 of ABO gene in 100 A3 and A3 B blood donors samples.

STUDY DESIGN AND METHODS: ABO serologic analyses of 12,283 blood donors of blood groups A and AB allowed the detection of 13 A3 and 87 A3B samples. Initially, DNA amplification was performed using sequence specific polymerase chain reaction (PCR-SSP) to identify 467C>T, 829G>A, 871G>A and 1060delC polimorphisms of exon 7 of ABO gene, followed by direct DNA sequencing.

RESULTS: New ABO variants were detected in 5/13 (38.5%) of A3 and in 38/87 (43.7%) of A3B samples. ABO*A302/ABO*A301 genotype was found in 30.7% A3 and, ABO*A302/ABO*B104 in 17.1% of A3B samples. The 871G>A mutation previously reported only in A3B individuals was found in 9 blood samples tested as A3 in our study. For the first time, mutations between 441–450 nucleotides of exon 7 of ABO gene was detected in 39 samples (single nucleotide polimorphisms and deletions) of A3 and A3B subgroups.

CONCLUSION: This is the first large molecular study of A3 and A3B samples. Sistematic analysis of A3 and A3B samples reveals new ABO variants caused by different molecular events. Mutations between 441 and 450 nt. of exon 7 are critical for transferase A expression in individuals typed as A3 and A3B.

Author notes

Disclosure: No relevant conflicts of interest to declare.