Gene-environment interaction
- Concept
An exposure harms people with a certain gene variant far more, or a gene only causes disease when an exposure is present.
What it is
Gene-environment interaction exists when the effect of an exposure on disease risk depends on genotype, or the effect of a genotype depends on exposure. It is a form of effect modification assessed with a 2 × 4 table (genotype × exposure) and read on the multiplicative or additive scale. It explains why the same exposure affects people differently and underlies the idea of personalised prevention.
Worked example
- Case-control study, reference with neither variant nor exposure: 50 cases and 200 controls.
- Variant only: 20 cases and 80 controls: OR = (20/80)/(50/200) = 0.25/0.25 = 1.0.
- Exposure only: 60 cases and 120 controls: OR = 0.5/0.25 = 2.0.
- Variant and exposure: 60 cases and 40 controls: OR = 1.5/0.25 = 6.0.
- Expected with no multiplicative interaction: 1.0 × 2.0 = 2.0. Observed 6.0: three times more.
- Additive scale: RERI ≈ 6.0 − 1.0 − 2.0 + 1 = 4.0, also positive.
- Reading: the exposure triples its effect in carriers; avoiding it is a priority for them.
Examples of gene-environment interaction
| Genotype | Exposure | Result |
|---|---|---|
| Phenylketonuria | Dietary phenylalanine | Neurological damage that a restricted diet prevents |
| Alpha-1 antitrypsin deficiency | Smoking | Early and severe emphysema |
| G6PD deficiency | Fava beans and oxidant drugs | Haemolysis |
| Slow acetylator (NAT2) | Aromatic amines | Higher risk of bladder cancer |
Markers
- G × E
- 2 × 4 table
- Case-only
In practice
- Newborn screening for phenylketonuria is the success story: the genotype is detected and the environment (diet) is changed.
- Pharmacogenetics applies the same idea: genotype changes the effect or toxicity of a drug.
- For most common diseases, known interactions do not yet change recommendations.
Common pitfalls
- Testing many gene-exposure combinations without correcting for multiple comparisons.
- Measuring exposure poorly: misclassification dilutes the interaction.
- Using the case-only design when genotype influences the chance of being exposed.
- Reporting interaction without stating the scale (additive or multiplicative).
Test yourself
Think of the answer, then tap the question to see it.
OR for the variant alone 1.0, exposure alone 2.0 and both 6.0. Is there multiplicative interaction?
Yes: the expected value would be 1.0 × 2.0 = 2.0 and 6.0 is observed.
What assumption does the case-only design need?
That genotype and exposure are independent in the population the cases come from.
Which gene-environment interaction has an effective prevention?
Phenylketonuria: newborn screening finds the genotype and a low-phenylalanine diet prevents the damage.
Why do many gene-environment findings fail to replicate?
Small samples, poorly measured exposure and many tests without correction for multiple comparisons.
Elsewhere in DurgiPedia
Connections
Educational content on epidemiological and statistical methods; the examples use made-up numbers to teach the calculation. Not a clinical or legal guide: current Colombian rules are in the official sources.
Sources: Genetic Epidemiology (Centers for Disease Control and Prevention, 1997); What is heritability?: MedlinePlus Genetics (National Library of Medicine (MedlinePlus), 2021).
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Representative model, for educational purposes only.