SERPINA1 and alpha 1-antitrypsin deficiency: ,6 Individuals homozygous for the normal M allele (PI∗MM) typically have serum AAT levels of 17-47 μM (102-254 mg/dL), whereas individuals homozygous for the Z allele (PI∗ZZ), which is associated with severe AATD, have serum AAT levels <10 μM (<52 mg/dL).7