Alpha-1-antitrypsin is a so-called protease inhibitor, a type of enzyme inhibitor. It is produced in the liver but exerts its effects in the lungs, where it regulates immune cell activity. This regulation is crucial, and an overactive immune response can cause serious lung diseases.

However, some individuals carry a genetic mutation that causes the alpha-1 protein to fold incorrectly. As a result, too little functional alpha-1 is produced, and insufficient amounts reach the lungs.

The mutation is inherited from one or both parents. About 1 in 20 people in Europe carry the heterozygous form of the mutation—inherited from only one parent—and often experience no symptoms or only mild ones. In contrast, the rarer homozygous form, inherited from both parents, affects approximately 1 in 2000 individuals and is much more severe.