Two ways of asking the same question — parent-reported diarrhoea at around age one, and the same thing confirmed by a doctor — and one study found both point at the same locus: FUT2, the gene that decides whether the gut lining is a welcoming place for rotavirus and norovirus.
The two variants on this page come from a single study, under two different ways of defining the same event: parent-reported diarrhoea at around age one, and the same thing with a doctor's diagnosis behind it. The study's own conditional analysis connects them — both point at the same underlying signal.
Bustamante et al. 2016 meta-analysed genome-wide association data on childhood diarrhoea across 5,758 participants, with 3,784 more in replication, using parental questionnaires and medical records collected around two age windows. Conditional analysis identified rs601338, a stop-gain variant (W154X) in FUT2, as the likely causal variant behind the signal seen at both of this page's variants. Children carrying the risk-reducing allele produce a truncated, non-functional FUT2 protein.
FUT2 is well known outside this one study. It controls whether histo-blood group antigens are secreted into body fluids and the lining of the gut — whether someone is a genetic "secretor" or "non-secretor." Secretor status is an established determinant of susceptibility to rotavirus and norovirus, the two leading causes of infectious diarrhoea in young children worldwide: the antigens these viruses use to attach to gut cells are the same ones FUT2 controls the secretion of. A non-functional copy makes the gut lining a less hospitable place for them to attach — which is a plausible mechanism, not merely a statistical association, for why the protective allele lowers diarrhoea risk.
Diarrhoea in an infant that is severe, bloody, or accompanied by signs of dehydration (reduced wet nappies, sunken eyes, lethargy) needs medical attention regardless of genotype. Rotavirus vaccination, already part of the standard infant immunisation schedule in most countries, remains the single largest lever against the leading cause of severe diarrhoea in this age group — nothing here is a substitute for it.
FUT2 secretor status is also relevant elsewhere on this catalogue — it is one of the best-replicated genetic findings in nutrition and gut microbiome research, affecting vitamin B12 levels and the composition of gut bacteria, among other things. This page covers its specific link to early-childhood diarrhoea risk.
Both trait strings behind this page's variants describe the same event measured two ways in the same study — this page treats them as one finding rather than two, which is what the study's own conditional analysis supports.
What a 23andMe/AncestryDNA export or raw VCF can and can't tell you about Diarrhoeal Disease in Infancy comes down to these specific, well-studied positions — not a diagnosis.
Databases, guidelines and references
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Diarrhoeal Disease in Infancy. MyGeneLog™. https://www.mygenelog.com/conditions/diarrhoeal-disease-in-infancy
No single gene provides protection like that. This variant shifts risk by changing susceptibility to specific viruses (rotavirus and norovirus) that use the antigens FUT2 controls to attach to the gut lining. Vaccination and standard hygiene measures matter regardless of genotype.
They come from the same study measuring diarrhoea two ways — parent-reported and doctor-diagnosed — around the same age. The study's own analysis shows both point at the same underlying FUT2 signal, which is why this page treats them as one finding.
A secretor is someone whose FUT2 gene lets histo-blood group antigens be released into body fluids and the gut lining. Rotavirus and norovirus, the leading causes of infectious diarrhoea in young children, use those same antigens to attach to gut cells — so secretor status is a real, mechanistic factor in susceptibility, not just a statistical correlation.
Diarrhoea that is severe, bloody, or comes with signs of dehydration needs medical attention regardless of any genotype. This page is about a small shift in susceptibility measured across a large study population, not a diagnostic or predictive tool for an individual episode.
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