Molecular basis for para-Bombay phenotypes in Chinese persons, including a novel nonfunctional FUT1 allele

The para-Bombay phenotype is characterized by H-deficient or H-partially deficient red blood cells (RBCs) in persons who secrete ABH antigens in their saliva. The studies that determined the genotypes for two Chinese individuals with the para-Bombay phenotype are described.

RBC phenotypes were characterized by conventional serologic methods. Exons 6 and 7 of the ABO gene were amplified, as well as the entire coding region for FUT1 and FUT2, with four independence polymerase chain reactions (PCRs) from genomic DNA. PCR products were excised, purified from agarose gels, and sequenced directly. Mutations of FUT1 were identified by TOPO cloning sequencing.

For both individuals, RBC ABO genotypes correlated with ABH substances in their saliva. One individual (a patient) had two heterozygous mutations of FUT1 by direct DNA sequencing, namely, a C-->T heterozygous mutation at position 293(C293T) and AG heterozygous deletion (CAGAGAG-->CAGAG) at position 547 to 552. These two mutations were confirmed to be compound heterozygotes; that is, each mutation was determined to be on a separate homologous chromosome by TOPO cloning sequencing. The FUT2 genotype was Se(357)Se(357). The other individual (a blood donor) had an AG deletion at position 547 to 552 homozygous allele in FUT1. The FUT2 genotype was Se(357)Se(357,385). C293T mutation can cause Thr/Met at amino acid position 98. AG deletion at position 547 to 552 caused a reading frameshift and a premature stop codon.

A novel nonfunctional FUT1 allele C293T was identified in a person with the para-Bombay phenotype. This rare H-deficient phenotype may result from different nonfunctional alleles.