Alpha-1-antitrypsin is a plasma protease inhibitor that accounts for 90% of the total anti-protease activities in the blood. Reduced serum levels of this protein in certain individuals constitute a genetic disorder known as alpha-1-antitrypsin deficiency, which predisposes affected individuals to high risk of developing chronic obstructive pulmonary emphysema. The deficiency is characterized by the presence of variant alpha-1-antitrypsin of the Z or S phenotypes instead of the normal M phenotype, and is inherited by an autosomal recessive trait. Serum levels of alpha-1-antitrypsin in ZZ homozygotes and SZ heterozygotes are 12 and 35% of the normal individuals, respectively. The frequencies of the Z and S genes are such that 1/3000 to 1/4000 of caucasians in the United States are of the ZZ phenotype and 1/800 are of the SZ phenotype. It has been estimated that 80-90% of ZZ homozygotes will develop pulmonary emphysema of various severity, and there is no cure for this genetic disorder at the present time. Subtle amino acid substitutions in alpha-1-antitrypsin between the Z and S deficient phenotypes and the normal M phenotype have been reported. Since only limited amino acid sequence of the normal and variant proteins have been determined, whether there are additional amino acid substitutions between these proteins are not known at the present time. Using Recombinant DNA Technology, we propose to isolate and characterize the human Alpha-1-antitrypsin gene from normal and deficient individuals by molecular cloning. Comparison of the structural organization and nucleotide sequence between the cloned genes should reveal any additional amino acid substitutions in the variant proteins and would thereby establish the molecular basis of the deficiency at the gene level. This information will then permit the development of a simple and reliable method for prenatal diagnosis of the genetic disorder by gene mapping. Early detection of individuals with the genetic disorder will permit better management of the deficiency, which will in turn reduce the risk of their developing pulmonary emphysema later in life. Finally, attempts will be made to better understand the cause(s) of the deficiency by examining the expression of the deficient genes after their introduction through DNA mediated gene transfer into a human hepatoma cell line which synthesizes and secretes normal Alpha-1-antitrypsin.
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