What role does FUT2 play in allergy?

FUT2 (fucosyltransferase 2) determines secretor status, i.e., whether fucosylated antigens (e.g., Lewis b) are present in body fluids like saliva and mucus. These antigens shape the microbiome and mucosal immune responses. Studies indicate that non-secretors (homozygous for the inactive allele rs601338) may have a slightly increased risk for allergic conditions such as hay fever, asthma, and eczema. The association has been replicated in several GWAS and cohort studies, but effect sizes are small (OR ~1.1–1.3) and modifiable by environment. Mechanistically, altered bacterial/viral binding to mucosa and immune regulation are proposed. Evidence is moderate but insufficient for predictive testing. Direct-to-consumer tests for FUT2 should be viewed cautiously, as the individual impact on allergy development is limited.