[Deficiency of alpha-1-antitrypsin and the allele Pi nul]

Alpha-1-antitrypsin is a glycoprotein in human serum that inhibits several proteases. It is a polymorphic protein. A single autosomal locus (Pi), with multiple codominant alleles is responsible of the synthesis of alpha-1-antitrypsin. Of particular interest are alleles that lead to lower than normal concentrations of alpha-1-antitrypsin in serum, namely, PiS, PiP and PiZ. Some of these subjects carry a high risk of developing chronic obstructive pulmonary disease, especially when they are homozygotes for PiZ. In children, cirrhosis of the liver are also found in association with homozygosity for PiZ. recently, TALAMO discovered a subject whose serum contained no alpha-1-antitrypsin; this was the first case of total deficiency, and the patient carried a double dose of the so-called Pi--allele (Pi nul). We were able to demonstrate that a single dose of this allele exists in three families which we have studied in this paper. In a fourth family, the propositus carries Pi-- in duplicate. We report here the second case of the strange homozygous phenotype, Pi--. Surprisingly, we have found that alpha-1-antitrypsin is not completely absent in this serum; its concentration is 200 times lower than normal (less than 10 microgrammes per ml). At the moment, the existence of the Pi-- allele is obvious, but the significance of this small quantity of alpha-1-antitrypsin in the serum of such a patient remains unknown.