rs28929474
Alpha-1 antitrypsin, Z allele
What this position does
Alpha-1 antitrypsin protects lung tissue from an enzyme released by white blood cells. The Z version folds badly, gets stuck in the liver, and leaves the lungs under-protected. It is the most common serious inherited cause of emphysema and it is very widely missed.
What each result means
| If you carry | What it means |
|---|---|
| No copies of the effect version CC | You do not carry the Z version Neither copy carries the Z allele. |
| One copy CT | You carry one copy, which matters most if you smoke Usually mild, but smoking matters much more for a carrier than for anyone else. This is the single most actionable thing on this page for a smoker. |
| Two copies TT | You carry two copies, and a simple blood test is the right next step The genotype found in most people with clinically significant alpha-1 antitrypsin deficiency. It is treatable and chronically under-diagnosed, often for decades. A serum alpha-1 antitrypsin level is a cheap, ordinary blood test and is the right next step. |
Worth knowing. Deficiency is defined by the protein level in your blood, not by a genotype. If this comes back positive, the blood test is what settles it.
How common each version is
| Ancestry group | T (the effect version) | |
|---|---|---|
| African | 0.0% | |
| American | 0.4% | |
| East Asian | 0.0% | |
| European | 1.7% | |
| 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 | CC | CT | TT |
|---|---|---|---|
| African | 661 / 661 | 0 / 661 | 0 / 661 |
| European | 486 / 503 | 17 / 503 | 0 / 503 |
| East Asian | 504 / 504 | 0 / 504 | 0 / 504 |
| South Asian | 489 / 489 | 0 / 489 | 0 / 489 |
| American | 344 / 347 | 3 / 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
Stoller and Aboussouan, Alpha1-antitrypsin deficiency, The Lancet (2005)
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 rs28929474?
rs28929474 is a position in the SERPINA1 gene on chromosome 14. Alpha-1 antitrypsin protects lung tissue from an enzyme released by white blood cells. The Z version folds badly, gets stuck in the liver, and leaves the lungs under-protected. It is the most common serious inherited cause of emphysema and it is very widely missed.
What does it mean if I have TT at rs28929474?
You carry two copies, and a simple blood test is the right next step. The genotype found in most people with clinically significant alpha-1 antitrypsin deficiency. It is treatable and chronically under-diagnosed, often for decades. A serum alpha-1 antitrypsin level is a cheap, ordinary blood test and is the right next step.
What does it mean if I have CC at rs28929474?
You do not carry the Z version. Neither copy carries the Z allele.
How do I find out my rs28929474 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.