SERPINA1 and alpha 1-antitrypsin deficiency: In the United States (US), the most common pathogenic AATD variants in order of prevalence are the S, Z, F (c.739C > T; p.Arg247Cys), and I (c.187C > T; p.Arg63Cys) variants, all of which result in reduced levels/functionality of AAT [16, 17].