rs1815739
Fast-twitch muscle protein
What this position does
ACTN3 makes a structural protein found only in fast-twitch muscle fibres. Roughly a fifth of people carry two broken copies and make none of it at all, with no ill effect whatsoever.
What each result means
| If you carry | What it means |
|---|---|
| No copies of the effect version CC | Two working copies You make alpha-actinin-3. This genotype is over-represented among elite sprinters and power athletes, though the effect on any individual is small next to training. |
| One copy CT | One working copy The most common genotype worldwide. You make alpha-actinin-3 and sit between the two extremes. |
| Two copies TT | No working copies You make no alpha-actinin-3 at all. This is completely normal, shared with roughly a fifth of humanity, and is slightly over-represented among endurance athletes. |
Worth knowing. Genotype explains a low single-digit percentage of the variation in sprint performance. It does not predict whether you will be good at anything.
How common each version is
| Ancestry group | T (the effect version) | |
|---|---|---|
| African | 11.5% | |
| American | 57.2% | |
| East Asian | 44.3% | |
| European | 43.4% | |
| South Asian | 58.7% |
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 | CC | CT | TT |
|---|---|---|---|
| African | 512 / 661 | 146 / 661 | 3 / 661 |
| European | 156 / 503 | 257 / 503 | 90 / 503 |
| East Asian | 155 / 504 | 251 / 504 | 98 / 504 |
| South Asian | 77 / 489 | 250 / 489 | 162 / 489 |
| American | 56 / 347 | 185 / 347 | 106 / 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: Trait.
Where this fits
Common questions
What is rs1815739?
rs1815739 is a position in the ACTN3 gene on chromosome 11. ACTN3 makes a structural protein found only in fast-twitch muscle fibres. Roughly a fifth of people carry two broken copies and make none of it at all, with no ill effect whatsoever.
What does it mean if I have TT at rs1815739?
No working copies. You make no alpha-actinin-3 at all. This is completely normal, shared with roughly a fifth of humanity, and is slightly over-represented among endurance athletes.
What does it mean if I have CC at rs1815739?
Two working copies. You make alpha-actinin-3. This genotype is over-represented among elite sprinters and power athletes, though the effect on any individual is small next to training.
How do I find out my rs1815739 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: Trait.