Continuously updated · last reviewed Sep 5, 2026
Each page covers one condition properly: what it actually is and what it feels like, what causes it, how common it really is and in whom, and how it's diagnosed — followed by the specific variants with a replicated link to it, and, where the research supports it, how genetics can change the way a medicine behaves.
Written in two registers so one page serves both readers: plain language first, then a clinical detail section with the precise terminology, effect sizes and diagnostic thresholds. Every claim is sourced from freely-available published research and cited on the page, so you can check us — or hand the page to your doctor. 27 conditions so far, growing continuously, and free to reuse with attribution (CC BY 4.0).
The ABO gene variant that creates blood type O by disabling its enzyme, why blood type matters for transfusion, and which disease links (clotting risk, malaria, cholera) are strong versus which (COVID-19, cancer risk) remain modest or contested.
Read more → MetabolicA common East Asian genetic variant that leaves the body unable to fully break down a toxic alcohol byproduct, causing facial flushing and, with regular drinking, a substantially elevated risk of esophageal cancer.
Read more → NeurologicalAPOE is the strongest common genetic influence on late-onset Alzheimer's disease. Its e4 form raises risk and e2 lowers it, but APOE genotype predicts probability rather than destiny.
Read more → DermatologicMale pattern baldness is strongly heritable and linked to a variant in the androgen receptor gene on the X chromosome. That partly explains the 'blame your mother's father' folklore, but dozens of other genes also matter.
Read more → CardiovascularA common DNA variant near the PITX2 gene is the strongest and most consistently replicated genetic risk factor for atrial fibrillation, the most common irregular heart rhythm and a major cause of stroke.
Read more → SensoryThree coding changes in one bitter receptor gene decide whether compounds like PTC and PROP taste intensely bitter or of almost nothing. It is the strongest genetic association on this site, and one of the oldest known human polymorphisms.
Read more → PharmacogenomicsA common CYP1A2 variant affects how quickly the body clears caffeine. A widely repeated claim that 'slow' metabolizers face higher heart-attack risk from coffee rests on limited evidence that has not held up well in larger studies.
Read more → ImmunologicA 32-base-pair deletion in the CCR5 gene that removes a key HIV-1 entry receptor from immune cells; two copies confer strong resistance to CCR5-tropic HIV-1, while one copy slows disease progression without preventing infection.
Read more → SensoryThe bitter taste receptor T2R38 is not only on the tongue. It also lines the sinuses, where it detects bacterial signalling molecules and answers with nitric oxide — and the genotype that tastes nothing defends the sinuses less well.
Read more → ImmunologicA lifelong inflammatory bowel disease that can affect any part of the digestive tract. Its genetics are unusually well mapped — NOD2 was the first susceptibility gene ever found for a common complex disease, and IL23R showed a drug class where to aim.
Read more → HematologicA promoter variant that silences the Duffy antigen on red cells, protecting against Plasmodium vivax malaria and causing a normal, lower neutrophil count that is routinely and wrongly treated as disease in people of African ancestry.
Read more → HematologicA common inherited change in the F5 gene that makes blood slightly slower to switch off clotting, raising the risk of deep vein thrombosis and pulmonary embolism. Most carriers never have a clot.
Read more → ImmunologicA common FUT2 variant determines whether ABO blood-group antigens appear in saliva, gut mucus and other secretions; the roughly one in five people who are "non-secretors" are strongly resistant to the dominant norovirus strains.
Read more → OphthalmicGlaucoma is a group of eye diseases that silently damage the optic nerve. A variant near SRBD1 has been linked to normal-tension glaucoma in Japanese cohorts, but evidence outside that population is thin.
Read more → MetabolicAn inherited condition in which the body absorbs more iron from food than it needs. Over decades the surplus iron can build up in the liver, heart, pancreas and joints and cause damage.
Read more → CardiovascularCommon variants near the APOA5 gene are associated with modestly higher average triglyceride levels. They contribute a small shift, not a diagnosis, and very high triglycerides mainly matter because of pancreatitis risk.
Read more → MetabolicWhether you can comfortably drink milk as an adult comes down largely to a single DNA switch near the LCT gene. Persistent lactase activity is the evolutionary exception in humans, not the default.
Read more → MetabolicTwo very common MTHFR variants modestly change how efficiently one folate-processing enzyme works. They are heavily over-claimed online; here is what the published evidence actually supports, and what it does not.
Read more → MetabolicA common variant near the FTO gene is linked to a small average increase in body weight and BMI by nudging appetite regulation. Most carriers never become obese — environment and behavior still matter most.
Read more → PharmacogenomicsA common OPRM1 variant alters the mu-opioid receptor and has been studied in relation to opioid dose requirements and naltrexone response, but CPIC found the evidence too weak and inconsistent to support any clinical dosing recommendation.
Read more → NeurologicalA common neurological sleep-related movement disorder causing an overwhelming urge to move the legs, worse at rest and in the evening and relieved by movement, which fragments sleep and often runs in families.
Read more → SensoryOdorant receptors are the largest gene family in the human genome, and they differ enormously between people. The result is that two people can meet the same molecule and only one of them smells anything at all.
Read more → PharmacogenomicsMuscle aches are the most common reason people stop taking statins. A common variant in SLCO1B1, the liver transporter that pulls statins out of the bloodstream, is linked to higher statin levels and higher myopathy risk.
Read more → DermatologicHow two pigmentation variants (IRF4 rs12203592 and SLC45A2 rs16891982) relate to freckling and sun sensitivity, what they do and do not say about melanoma and skin cancer risk, and why early detection matters most.
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