Molecular heterogeneity of the A(3) subgroup

The molecular characterization of the subgroup A(3) remains unclear. Four u nrelated A(3) blood donors were studied. Family studies were possible in th ree of them. The A(3) subgroup was defined by immunohaematological evaluati on with four different commercially available serums, Exons VI and VII of t he ABO gene, responsible for 91% of the catalytic active part of the glycos yltransferase, were amplified and subjected to direct sequencing, The resul ts in all samples showed heterozygosity for the G261 deletion, In the A(3) allele, the following associations were found: C467T mutation and 1060C del etion in one A(3) blood donor and in another G829A and 1060C. In one case, only the 1060C deletion was demonstrated in the A(3) allele. One blood dono r presented the T646A and the G829A mutations in homozygosity. It was concl uded that the Ag blood group is very heterogeneous at the molecular level.