The S allele (Glu264Val) is one of the most frequent variants related to AATD, causing a 40% decrease in circulating AAT protein, with mean serum levels in homozygous PI*SS subjects of 0.82 g/L (95% CI 0.73 to 1.00 g/L) [5]. Here, SERPINA1 is linked to alpha 1-antitrypsin deficiency.