[Gene therapy--basic principles]

Recombinant DNA technology allows the cloning of genes and their expression in vitro. Cloned genes are central to human gene therapy. The principle of gene therapy is based on three different strategies: gene replacement in classic genetic diseases which are caused by a single gene defect that conforms to the rules of Mendelian inheritance; gene augmentation for the treatment of complex genetic diseases by providing the cell with a new function; block of gene expression in acquired genetic diseases such as infections and malignancies.