Analysis of the Alpha-1-Antitrypsin Deficient Alleles M3S, MZ, and ZZ by Biochemical and Molecular Methods: A Family Study

Abstract

Deficiency of alpha-1-antitrypsin (alpha(1)-AT, a major protease inhibitor controlling tissue degradation) is a genetic disorder transmitted in a codominant autosomal form. It has more than 100 genetically determined variants. This study attempted to determine the degree of association between serum alpha(1)-AT levels and phenotypes and to provide a strategy for reliable laboratory evaluation of deficiencies. The study group consisted of a 38-year-old male proband with clinical features of emphysema, his first-degree relatives, and healthy controls. Family history revealed a four-generation pedigree. Genomic DNA was isolated from peripheral blood leukocytes. Alpha-1-AT levels were determined from human serum by immunonephelometry. Phenotypes were determined by isoelectric focusing of blood samples. DNA sequences of coding exons were analyzed by the amplification DNA technique and direct sequencing. Inheritance and plasma levels of the ZZ, MM, M3S, and MZ phenotypes were confirmed by the family study. In the family members with deficiencies, plasma concentrations were 22.55% +/- 5.15 (ZZ), 84.18% +/- 5.18 (M3S), and 61.06% +/- 7.15 (MZ) of the normal MM level. We found a close association between alpha(1)-AT level and genotype. A combination of genotyping, quantification, and phenotyping is the optimal strategy for the laboratory evaluation of alpha(1)-AT deficiency.