FUT1 variants responsible for Bombay or para-Bombay phenotypes in a database

Rare individuals with Bombay and para-Bombay phenotypes lack or have weak expression of the ABO(H) antigens on surface of red blood cells due to no or very weak H-type α(1,2)fucosyltransferase activity encoded by FUT1. These phenotypes are clinically important because subjects with these phenotypes can only accept transfusions of autologous blood or blood from subjects with the same phenotypes due to the anti-H antibody. To survey FUT1 alleles involved in Bombay and para-Bombay phenotypes, the effect of 22 uncharacterized nonsynonymous SNPs in the Erythrogene database on the α(1,2)fucosyltransferase activity were examined by transient expression studies and in silico analysis using four different online software tools. Two nonfunctional alleles (FUT1 with c.503C>G and c.749G>C) and one weakly functional allele (with c.799T>C) were identified in transient expression studies, while the software predicted that the proteins encoded by more alleles including these would be impaired. Because both nonfunctional FUT1 alleles appear to link to the nonsecretor alleles, homozygotes of these alleles would be of the Bombay phenotype. The present results suggest that functional assays are useful for characterization of nonsynonymous SNPs of FUT1 when their phenotypes are not available.