RESUMO
We investigated the molecular genetic basis of rare cisAB variants at the ABO locus in Chinese population. Serological techniques were performed to characterize erythrocyte phenotype of 12 discrepant samples and 116 randomly selected samples. Mutations of complete exon 6 and 7 including flanking intron in the ABO genes were screened by PCR and directly sequencing. The haplotypes of diverse genotypes were also analyzed by cloning sequencing. Twelve samples were identified as AweakB or ABweak phenotype by serological technology, and were also identified as cisAB variants including four genotypes by directly sequencing. Two cisAB alleles were found by haplotype sequencing. One allele was cisAB01, in which four nucleotide acid alterations were observed (467C>T and 803G>C in exon 7, 163T>C and 179C>T in intron 6); the other allele maintained a nucleotide acid of A101 allele (803G) compared with B101 allele, which resulted in a polypep-tide containing 176G, 235S, 266M, and 268G four amino acids. This is a novel allele, which has been named cisAB05 by Blood Group Antigen Gene Mutation Database. According to systematically investigation of the molecular genetic basis of the cisAB variants in Chinese population, we found a novel cisAB05 allele and presumed that the cisAB01 allele is derived from homologues exchange of A101-B101 combination.