Genetic polymorphism of serum alpha-1-protease inhibitor (alpha-1-antitrypsin): Pi i, a deficient allele of the Pi system.

The microheterogeneity of the I allele of the Pi system of APi (alpha-1-antitrypsin) was studied in 43 individuals with the new PAGIF technique. The unique aspect of the I allele product (unequal distribution of bands 4 and 6), previously demonstrated with acid-starch gel, was confirmed. In addition, two subtypes of the Pi I allele--I1 and I2--were clearly distinguished. Serum concentrations of APi associated with the expression of the I allele were significantly decreased (68% of normal values) and thus very similar to those associated with the expression of the S allele. This indicates that the I allele can be considered as a "deficient" allele of the Pi system.