One gene, more than two thousand described variants, and a treatment that is chosen by which variant somebody carries rather than by the diagnosis they have. It is the clearest case anywhere of why the variant is the unit that matters.
CFTR makes a channel that sits in the surface of cells lining the airways, the pancreas and the sweat glands, and moves chloride across it. Water follows chloride. When the channel is missing or does not work, the fluid on those surfaces is thicker than it should be — and mucus that should be cleared instead stays, which is why the lungs and the pancreas take the damage.
Cystic fibrosis is recessive: it takes two altered copies, one from each parent. A person with one is a carrier, does not have the condition and will not develop it. Roughly 1 in 25 people of European ancestry carries a CF-causing variant, which makes carriers common and the condition itself uncommon — around 1 in 2,500 to 3,500 births in those populations, and less frequent in most others.
For most of its history cystic fibrosis was treated by managing what the broken channel caused: physiotherapy, antibiotics, enzymes with food. Nothing addressed the channel.
Ivacaftor did, and it did so for some people and not others with the same diagnosis. It is a potentiator: it holds open a channel that has reached the cell surface but opens poorly. If somebody carries a gating variant — G551D is the archetype — it works. If they carry two copies of F508del, the commonest CF variant of all, it does not, because that protein never arrives at the surface for anything to hold open.
Two people, one diagnosis, one drug, opposite answers, decided by which change they carry. That is why the variant and not the diagnosis is the unit that matters, and it is stated more plainly here than anywhere else on this site.
The gap ivacaftor left was the reason for the combination therapies that followed, which pair a corrector — a molecule that helps the protein fold and reach the surface — with the potentiator. That extended treatment to people carrying F508del, who are the majority. The principle did not change: the treatment is still chosen by genotype.
A consumer genotyping array tests a few dozen CFTR variants out of more than two thousand described. A file with no CFTR variant in it is not a negative carrier result. Panels are also weighted towards the variants common in people of European ancestry, so they miss proportionally more in everybody else.
If carrier status matters to you — because you are planning a pregnancy, or because it runs in your family — the answer comes from a clinical carrier screen, not from a raw data file. That is the one thing on this page worth acting on.
Positions joined since this page was written
What this is The text above discusses the variants this page was written around. Since then the catalogue has joined 4 more positions to it, by shared trait or shared paper. They are listed here by the paper each came from; the text does not describe them, and each variant page carries that study's own record.
Zhou YH et al. 2023, American journal of respiratory and critical care medicine rs12009976 (near AGTR2), rs56108664 (near MIR4456), rs485845 (near APIP) — PMID:36921087
Gong J et al. 2019, PLoS genetics rs61948108 (ATP12A) — PMID:30807572
2026-04-01 · Vertex Pharmaceuticals (FDA label expansion covering any CFTR variant shown to still produce CFTR protein, not just a fixed list of named mutations)
FDA expanded the approved-use labels for two CFTR modulators -- Alyftrek (ages 6+) and Trikafta, which contains ivacaftor (ages 2+) -- from a fixed list of named mutations to any CFTR variant shown, by clinical or lab data, to still let the gene make CFTR protein: 564 variants qualify for Alyftrek, 521 for Trikafta. About 800 more people with CF in the US are now eligible, bringing total eligibility to roughly 95% of the US CF population -- a real-world example of exactly the variant-by-variant pharmacogenomic matching this page profiles.
How it is diagnosed. Newborn screening picks up most cases in countries that run it, followed by a sweat chloride test — the sweat of somebody with cystic fibrosis is measurably saltier — alongside genetic testing. Diagnosis is not made from a genotype file, and a person who suspects it needs a clinic rather than a better array.
Variant classes. CFTR variants are grouped by what goes wrong: no protein made at all, protein made but not folded and never delivered (F508del), delivered but poorly opening (G551D and the other gating variants), reduced conductance, or reduced quantity. The class decides which drug can work, which is why the classification is not academic.
Carriers. Being a carrier is not a mild form of the condition. Some studies report small associations between carrier status and conditions such as pancreatitis or bronchiectasis, but a carrier does not have cystic fibrosis and the practical meaning of carrier status is reproductive.
Range of severity. Two people with the same CFTR genotype can differ substantially, because other genes and the environment modify the course. Genotype sets the range rather than the outcome — and CFTR-related conditions exist that are milder and later in onset than classical cystic fibrosis, including some presentations diagnosed in adulthood.
What a 23andMe/AncestryDNA export or raw VCF can and can't tell you about Cystic Fibrosis comes down to these specific, well-studied positions — not a diagnosis.
near AGTR2 · rs12009976
See detailed info →near MIR4456 · rs56108664
See detailed info →near APIP · rs485845
See detailed info →The studies behind these variants recruited participants from different ancestries — a result found in one population doesn't always transfer to another. Based on 7 of 13 linked studies with a resolved discovery ancestry.
Research-derived gene–drug associations only — not a prescription, dosing guide, or medical advice. Always follow your prescriber's guidance.
| Gene | Drug | What the research shows |
|---|---|---|
| CFTR | Ivacaftor | Ivacaftor is prescribed on the basis of which CFTR variant a person carries rather than on the diagnosis of cystic fibrosis, which makes it one of the clearest examples in medicine of genotype-directed treatment. It is a potentiator: it holds open a CFTR channel that has reached the cell surface but opens poorly. CPIC recommends it for people carrying at least one gating variant, of which G551D is the archetype, and specifically notes that it is not effective in people homozygous for F508del alone — that protein never reaches the surface, so there is nothing there for a potentiator to act on. The combination therapies developed since pair a corrector with the potentiator to address exactly that gap. Treatment is decided in a specialist clinic on confirmed clinical genotyping, and nothing here should be read as a reason to start, stop or change any medicine. (CPIC Guideline for Ivacaftor Therapy in the Context of CFTR Genotype (Clin Pharmacol Ther 2014, PMID 24598717).) |
| CFTR | Elexacaftor/tezacaftor/ivacaftor | Trikafta (elexacaftor/tezacaftor/ivacaftor) is the medicine that reached the people ivacaftor could not. Think of CFTR as a door that lets salt and water out of cells. Ivacaftor can only open a door that is already in place; with F508del, the most common typo, the door never gets there. Trikafta adds two medicines that move the door into place, and then ivacaftor opens it. The US label, revised in 2026, covers people aged 2 and older with cystic fibrosis who have at least one CFTR variant that still makes some CFTR protein or that tests show responds to it; if the variants are not known, an FDA-cleared CF genetic test comes first. If the variants make no protein at all, there is no door to fix. Because it can seriously harm the liver, it carries a boxed warning and needs regular liver blood tests. Whether to take it is decided with a specialist, and nothing here is a reason to start, stop or change a medicine. (TRIKAFTA (elexacaftor, tezacaftor, and ivacaftor) US prescribing information, revised 03/2026 (Vertex Pharmaceuticals; FDA label 212273s014).) |
| CFTR | Vanzacaftor/tezacaftor/deutivacaftor | Alyftrek (vanzacaftor/tezacaftor/deutivacaftor) works the same way as Trikafta: two medicines move the CFTR door into place, and deutivacaftor, a slightly modified ivacaftor, opens it. The difference you notice is that it is taken once a day. The US label, revised in 2026, covers people aged 6 and older with cystic fibrosis who have at least one CFTR variant that still makes some CFTR protein or that tests show responds to it, confirmed with an FDA-cleared CF genetic test if the variants are not known. It carries the same boxed warning about the liver. Whether to take it is decided with a specialist, and nothing here is a reason to start, stop or change a medicine. (ALYFTREK (vanzacaftor, tezacaftor, and deutivacaftor) US prescribing information, revised 03/2026 (Vertex Pharmaceuticals; DailyMed).) |
Databases, guidelines and references
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Cystic Fibrosis. MyGeneLog™. https://www.mygenelog.com/conditions/cystic-fibrosis
That does not follow, and it is the most important point on this page. More than two thousand CFTR variants have been described and a consumer array tests a few dozen — weighted towards those common in people of European ancestry. If carrier status matters to you, a clinical carrier screen answers it and a raw data file does not.
No. The condition is recessive and one altered copy does not cause it. Carrier status matters for family planning: if a partner is also a carrier, each pregnancy carries a 1 in 4 chance of an affected child. A genetic counsellor is the right place for that conversation.
Because CFTR variants break the channel in different ways. Ivacaftor holds open a channel that reached the cell surface but opens poorly. If the protein never reaches the surface — which is what F508del does — there is nothing for it to hold open, and a corrector is needed as well.
No. Cystic fibrosis is diagnosed with a sweat chloride test alongside clinical genetic testing, usually after newborn screening. A file can raise the question. It cannot answer it.
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