Which gene is responsible for secretor status based on saliva antigen expression?

• A. H gene
• B. Se gene
• C. AO gene
• D. ABO gene

Answer: (B)

The ability to express ABH antigens in saliva hinges on the Se gene. This gene encodes an α1,2-fucosyltransferase that adds fucose to the secretory precursor to produce the H antigen in secretions. If Se is functional, the H antigen appears in saliva, and depending on the ABO genotype, A or B antigens can be formed on that H substrate, giving detectable ABH antigens in saliva. If Se is nonfunctional, no H antigen is produced in secretions, so ABH antigens aren’t present in saliva, and the person is a nonsecretor. The H gene primarily affects H antigen on red cells, while the ABO gene determines whether A or B is added to the H antigen in secretors. There isn’t a separate AO gene in this context.