Polymerase chain reaction-mediated site-directed mutagenesis detection of Z and S alpha-1-antitrypsin alleles in family members.

Alpha-1-antitrypsin (A1AT) deficiency is an autosomal hereditary disorder with a reduction in serum A1AT levels. In a large family, we used a polymerase chain reaction (PCR)-mediated, site-directed mutagenesis assay to detect the two most common A1AT deficient variants, Z and S. By coamplification, using primers for both the Z and S mutations, we were able to detect heterozygous and homozygous genotypes for both mutations in a single reaction. We compared our results with phenotype studies obtained by standard immunofixation and isoelectric focusing techniques at two reference laboratories. Whereas PCR and isoelectric focusing agreed completely, there were five discrepancies in the results obtained by the immunofixation procedure. The reference laboratory that provided these discrepant results later informed us of a quality control problem that accounted for their error. The family study included 12 individuals representing three generations. Two individuals were MM homozygotes, three were MZ heterozygotes, four were MS heterozygotes, and three were SZ heterozygotes. A thirteenth family member was diagnosed as a ZZ homozygote at another institution. We have shown that this PCR coamplification technique provides accurate information about the M, S, and Z alleles that is at least as useful as current reference laboratory methodologies.