HFE
HFE sets how much iron your body absorbs from food. Two common variants — C282Y and H63D — reduce that control, and carrying two copies of C282Y is the main genetic cause of hereditary hemochromatosis, a condition where iron slowly builds up in the liver, joints, and heart. The critical detail most articles get wrong: the genotype is common, the disease is not. Most C282Y homozygotes never develop organ damage.
The body's iron thermostat.
Humans have no active way to excrete excess iron. The only control point is how much gets absorbed in the gut — which makes that regulation unusually important. HFE is part of the sensing system: it works with the transferrin receptor in the liver to gauge how much iron is circulating, and signals the liver to produce hepcidin, the master hormone that shuts absorption down when stores are full.
When HFE is defective, the liver under-produces hepcidin. The gut keeps absorbing iron as though the body were deficient, even when stores are already high. The excess is deposited in tissues — liver first, then joints, pancreas, heart, and skin — over decades.
Because the accumulation is slow and unopposed, the resulting disease is late-onset and gradual. It typically appears after age 40 in men, and later in women, whose iron losses through menstruation and pregnancy delay accumulation for years. That timeline is also why it is so treatable when caught: removing iron by regular blood draws (phlebotomy) prevents the organ damage entirely.
Two variants, very different weight.
Nearly all HFE testing comes down to two missense variants, plus one minor third:
A single C282Y copy — the most common finding by far — is carrier status. It is relevant to family planning and worth knowing, but it does not cause iron overload on its own.
Penetrance is the whole story.
Hereditary hemochromatosis is often described as if the C282Y/C282Y genotype meant inevitable disease. It does not. Population studies — most notably the large HEIRS study and subsequent cohort work — consistently find that while most homozygotes develop biochemical signs (raised transferrin saturation and ferritin), only a minority go on to clinical organ disease. Estimates vary by cohort and definition, but documented iron-overload disease affects a clear minority of male homozygotes and substantially fewer women.
- What can happen when it does progress: liver fibrosis and cirrhosis, joint pain (classically the second and third knuckles), diabetes, cardiomyopathy, and skin bronzing. Fatigue and joint pain are usually the earliest complaints.
- How it is actually diagnosed: blood tests, not genotype. Fasting transferrin saturation above roughly 45% together with elevated ferritin is what prompts investigation; genotype then explains the cause.
- Why it matters that it is treatable: phlebotomy — donating blood on a schedule — removes the excess iron. Started before organ damage, it gives a normal life expectancy. This is one of the few genetic findings where early awareness genuinely changes the outcome.
- Family relevance: the inheritance is autosomal recessive, so siblings of a homozygote have a 1-in-4 chance of the same genotype. Cascade testing of first-degree relatives is standard practice.
"The genotype tells you the risk pathway. Ferritin and transferrin saturation tell you whether it is actually happening. Only one of those two is a diagnosis."
Primary sources: MedlinePlus — HFE gene; GeneReviews — HFE Hemochromatosis; dbSNP rs1800562; EASL Clinical Practice Guidelines on haemochromatosis, J Hepatol 2022.
This is one of the genes consumer data actually covers well.
Unlike genes that depend on star alleles or repeat lengths, HFE comes down to two ordinary SNPs — and both are on essentially every consumer array:
- rs1800562 (C282Y) — the one that matters. Reported on the forward strand, the risk allele is A. An A/A result means two copies; G/A means carrier; G/G means neither.
- rs1799945 (H63D) — the risk allele is G. Useful mainly for interpreting a compound heterozygote alongside a single C282Y copy.
Two caveats worth keeping in mind. First, allele reporting conventions differ between services, so the same genotype can appear written differently depending on the strand orientation used — this is exactly the kind of thing worth having checked rather than eyeballing. Second, a consumer array result is not a clinical test: before anything is acted on medically, it should be confirmed alongside ferritin and transferrin saturation by a clinician.
That said, the practical value here is unusually high. If your raw data shows two C282Y copies, the useful next step is not alarm — it is a simple, inexpensive blood test that tells you whether iron is actually accumulating, decades before it could cause harm.