Molecular characterization of the P and I variants of alpha 1-antitrypsin

Two rare alpha 1-antitrypsin variants, Pi I and Plowell, originally defined at the protein level through isoelectric focusing, were characterized at the DNA level by the polymerase chain reaction and direct sequencing. The I variant was confirmed in one individual and three independent families to result from a CGC(Arg) to TGC(Cys) transition at codon 39, within exon II. In our population, the Pi I variant might be more common than expected. The Plowell allele was shown in one M3P heterozygous individual to be due to a GAT(Asp) to GTT(Val) change at codon 256, in agreement with a previous study based on hybridization with allele-specific oligonucleotides.