Carrier status: what your DNA file can and cannot show
This is the category people most often look at before starting a family, and the one where the gap between what a file covers and what people assume it covers is widest.
What does it mean to be a carrier?
You carry two copies of most genes, one from each parent. For recessive conditions, one working copy is enough — a carrier has a variant in one copy and no symptoms. It matters when two partners carry a variant in the same gene, because a child can then inherit the affected copy from both.
That is why carrier status is usually looked at as a pair rather than alone. One person's result, on its own, says very little about a future child.
Which conditions does a consumer DNA file cover?
Seven that are well represented on consumer arrays and clearly described in ClinVar: cystic fibrosis, sickle cell, Tay-Sachs, hereditary haemochromatosis, alpha-1 antitrypsin deficiency, factor V Leiden and prothrombin G20210A. Every one is read from a variant the chip observes directly, rather than estimated from the markers around it.
| What we look at | Markers |
|---|---|
| Cystic fibrosis Affects the lungs and digestion | CFTR — ΔF508 and other common variants |
| Sickle cell Affects red blood cells | HBB |
| Tay-Sachs Affects the nervous system | HEXA |
| Haemochromatosis The body stores too much iron | HFE — C282Y, H63D |
| Alpha-1 antitrypsin deficiency Affects the lungs and liver | SERPINA1 |
| Factor V Leiden Affects how your blood clots | F5 — Leiden |
| Prothrombin G20210A Affects how your blood clots | F2 — G20210A |
"Directly observed" is doing real work in that sentence. These are positions the chip actually reads, not positions estimated from neighbouring markers, which is why this category is more dependable than most.
Does a clear carrier result mean my children are not at risk?
No, and this is the most important sentence on the page. Consumer files cover a fraction of the known variants for these conditions — often the most common ones and little else. A clear reading means no variant was found among the ones your file can see. It is not an all-clear.
The clearest example is BRCA1 and BRCA2, which people ask about constantly. Consumer chips typically cover three founder variants common in Ashkenazi Jewish populations, out of thousands that are known. A file showing nothing there has ruled out almost nothing.
If there is a family history that worries you, or you are planning a pregnancy and want a real answer, the route is clinical carrier screening through a healthcare provider — which reads far more of each gene than any consumer array does.
When is it worth looking at carrier markers?
Most usefully before starting a family, and most usefully with a partner, since a single result rarely changes anything on its own. It is also worth knowing if a condition runs in your family — though in that case clinical testing, not a consumer file, is the thing that will actually answer the question.
Nothing here is a diagnosis, and none of it replaces a conversation with a clinician who knows your history.
The other categories
- Medicines How inherited differences change the way people process common medicines, which genes a consumer DNA file covers, and the two that it cannot read reliably at all.
- Nutrition Which nutrition and wellness markers a consumer DNA file covers, how strong the evidence behind them is, and why a blood test still beats a genotype.
- Fitness What a consumer DNA file can suggest about power versus endurance, response to training, injury predisposition and recovery — and the limits of all four.
- Traits Which everyday traits can be read from a consumer DNA file, which of them rest on strong single-gene evidence, and which are much weaker than they look.
- Ancestry How an ancestry breakdown is computed from a consumer DNA file, what mtDNA and Y haplogroups add, and why two services reading the same file disagree.