What this means

The S variant produces an Alpha-1 antitrypsin protein with mildly reduced secretion. PI*SS individuals have circulating levels around 60% of normal — usually enough to prevent lung disease, particularly if they don't smoke. PI*SZ compound heterozygotes have lower levels and a higher COPD risk, especially with smoking exposure. Compound heterozygote status isn't captured by this single SNP and requires looking at both S and Z alleles together.

Alpha-1 antitrypsin is a protein your liver makes that protects your lungs from damage. The S version makes a protein that's slightly harder for the body to release into the blood. People with two S copies end up with about 60% of the normal blood level — usually enough to keep the lungs healthy, particularly if they don't smoke. The combination that matters more clinically is one S copy plus one Z copy, which produces lower levels and a higher chance of COPD, especially with smoking. That combined picture isn't visible from this single DNA position alone — it requires looking at the S and Z versions together.

Caveats

• PI*SS alone rarely causes clinical disease.
• The compound PI*SZ state matters more clinically — check Z allele status separately.
• Smoking remains the dominant lifestyle risk modifier.

References

• Stoller & Aboussouan — A review of α1-antitrypsin deficiency (AJRCCM, 2012)
• Greene et al. — α-1 Antitrypsin deficiency (Nature Reviews Disease Primers, 2016)