Numerous diseases are associated with inherited or somatic mutations. In many cases, these mutations are present in the transcript region of genes, the products of which control important physiological functions including, for example, gene expression, cell signaling, tissue structure, and the metabolism and catabolism of various biomolecules. Mutations in these genes, which are often only single nucleotide changes (e.g., non-sense mutations, missense mutations), can have negative effects on the expression, stability and/or function of the gene product resulting in alterations in one or more physiological functions.
A number of different mutations have been identified in the Alpha-1 antitrypsin (AAT) gene. AAT is one of the primary circulating serum anti-proteases in humans. AAT inhibits a variety of serine proteinases, with neutrophil elastase being one of the most physiologically important, as well as inhibiting a number of metalloproteinases and other pro-inflammatory and pro-apoptotic molecules. AAT is normally produced within hepatocytes and macrophages, where hepatocyte-derived AAT forms the bulk of the physiologic reserve of AAT.
Approximately 4% of the North American and Northern European populations possess at least one copy of a mutant allele, known as PI*Z (Z-AAT) which results from a single amino acid substitution of lysine for glutamate at position 342 in the mature protein (position 366 in the precursor protein). In the homozygous state, this mutation leads to severe deficiency of AAT, and can result in two distinct pathologic states: a lung disease which is primarily due to the loss of antiprotease function, and a liver disease (present to a significant degree in approximately 10-15% of patients) due to a toxic gain of function of the Z-AAT mutant protein.
Investigational clinical gene therapy products for gene augmentation of AAT have been developed as potential treatments for lung disease using the recombinant adeno-associated viral (rAAV) vectors. Researchers have also applied genetic technologies in an effort to down-regulate the levels of AAT mRNA. One approach was to utilize hammerhead ribozymes designed to cleave AAT mRNA at a specific site. Another approach involves the use of RNA interference to decrease levels of the mutant mRNA transcript.