rs334
Sickle cell
What this position does
The single change that causes sickle cell disease in two copies and gives protection against severe malaria in one. It is the most studied human genetic variant there is.
What each result means
| If you carry | What it means |
|---|---|
| No copies of the effect version TT | You do not carry the sickle variant Neither copy carries the sickle variant. |
| One copy AT | Carrier, sickle cell trait One copy. Carriers are healthy in ordinary life, with some care needed at extreme altitude or extreme exertion, and it matters for family planning if a partner is also a carrier. |
| Two copies AA | Two copies, which means sickle cell disease Two copies cause sickle cell disease, which is diagnosed in childhood and would not first be discovered from a home DNA test. |
Worth knowing. Included knowing it usually cannot be read. The two letters at this spot are mirror images of each other, so there is no way to tell which DNA strand your testing company reported, and this report declines it rather than guessing. Sickle status is established by a cheap, definitive blood test.
This one cannot be read reliably from a home DNA test. Its two versions are mirror images of each other, so there is no way to tell which DNA strand your testing company reported. Sequencings declines it rather than guessing, and so should anything else.
How common each version is
| Ancestry group | A (the effect version) | |
|---|---|---|
| African | 10.0% | |
| American | 0.7% | |
| East Asian | 0.0% | |
| European | 0.0% | |
| South Asian | 0.0% |
1000 Genomes Project phase 3, via Ensembl, retrieved 2026-09-23. These groupings are coarse and flatten a great deal of internal diversity, particularly within Africa. A variant being common somewhere tells you where a piece of your ancestry probably comes from, and nothing else.
How many people carry each result
| Ancestry group | TT | AT | AA |
|---|---|---|---|
| African | 529 / 661 | 132 / 661 | 0 / 661 |
| European | 503 / 503 | 0 / 503 | 0 / 503 |
| East Asian | 504 / 504 | 0 / 504 | 0 / 504 |
| South Asian | 489 / 489 | 0 / 489 | 0 / 489 |
| American | 342 / 347 | 5 / 347 | 0 / 347 |
Counts of people, not modelled frequencies: every one of the 2,504 individuals sequenced by the 1000 Genomes Project phase 3, tallied by the genotype they carry. Deriving these from allele frequencies instead would assume random mating inside each group and undercount the homozygotes.
How to find out which you have
If you have taken a test with 23andMe, AncestryDNA, MyHeritage, Family Tree DNA, TellMeGen or Living DNA, this position is very likely already in the raw data file they gave you. You do not need another test.
One thing to watch if you look it up by hand: testing companies report some positions from one DNA strand and some from the other, and the file does not say which. Read the letters as they appear and you will get the opposite of the truth for some positions. Sequencings resolves that automatically.
Source
Coordinates and allele pair verified against Ensembl GRCh37. Direction of effect verified against VEP protein consequences or 1000 Genomes population frequency. Category: Health-adjacent.
Where this fits
Common questions
What is rs334?
rs334 is a position in the HBB gene on chromosome 11. The single change that causes sickle cell disease in two copies and gives protection against severe malaria in one. It is the most studied human genetic variant there is.
What does it mean if I have AA at rs334?
Two copies, which means sickle cell disease. Two copies cause sickle cell disease, which is diagnosed in childhood and would not first be discovered from a home DNA test.
What does it mean if I have TT at rs334?
You do not carry the sickle variant. Neither copy carries the sickle variant.
How do I find out my rs334 genotype?
If you have taken a home DNA test, this position is very likely in the raw data file you were given. Sequencings reads that file in your browser without uploading it, and resolves which DNA strand each position was reported from, which is the step most manual lookups get wrong.
This is reference information, not medical advice, and not a diagnosis. See the medical disclaimer. Category: Health-adjacent.