This is a protease inhibitor (Pi). Low serum levels of this antienzyme predisposes patients to early onset of emphysema and chronic liver disease. Ten percent of the adult population has the heterozygote genotype MZ in which intermediate levels of alpha1-antitrypsin is present. The incidence of liver disease in MZ is only mildly higher than the general population. Normal ranges by genotype: normal MM: more than 250mg/deciliter heterozygous MZ: 50 - 250 mg/dL homogygous ZZ: less than 50 mg/dL