SERPINA1 and alpha 1-antitrypsin deficiency: Alpha-1 antitrypsin deficiency (AATD) is the most common inherited disorder in adults; it is often under-diagnosed [6] and characterized by reduced plasma levels or the abnormal functioning of A1AT, a human blood serine protease inhibitor, which is encoded by the serine protein inhibitor-A1 (SERPINA1) gene.