SERPINA1 and alpha 1-antitrypsin deficiency: People with AAT deficiency, and especially those with severe AATD that are homozygous for the Z allele (Glu342Lys), have lower than normal intrapulmonary and circulating levels of AAT due to accumulation of the misfolded Z protein in the endoplasmic reticulum of hepatocytes, the principal source of AAT.