RESUMEN
<p><b>OBJECTIVE</b>To identify the genotypes of the 2 blood samples whose serological typing were difficult by DNA sequencing analysis, and to investigate the molecular genetic basis of their genotypes.</p><p><b>METHODS</b>The 2 blood samples were preliminary genotyped by PCR-SSP. The complete exon 6 and 7 in the ABO genes were amplified by PCR and the PCR products were directly sequenced and clonal sequenced in order to identify the genotypes.</p><p><b>RESULTS</b>The forward typing showed that both samples were weak A, while the reverse typing showed that the samples contained anti-A1. They were preliminarily genotyped as A/O1.</p><p><b>RESULTS</b>The sequencing analysis showed that the 2 samples contained the nt467C>T and nt745C>T mutation in the A allele, which resulted in an amino acid change from Proline (Pro) to Leucine (Leu) at codon 156 and also from Arginine (Arg) to Tryptophan (Trp) at codon 249.</p><p><b>CONCLUSION</b>Through serology results and sequencing analysis, the 2 samples are identified as rare A307 phenotypes.</p>