Augmentation Therapy -
In this type of somatic cell gene therapy, the functional gene is introduced In addition to the defective gene endogenous to the cell(s), i.e., the modified cells contain both the defective (endogenous) as well as the normal (introduced) copies of the gene. There are two general approaches to augmentation therapy.

The first approach was used in the first two patients on whom gene therapy was attempted to correct the genetic disorder called severe combined immune deficiency (SCID) syndrome produced by adenosine deaminase (ADA) deficiency.

(i) Normal ADA gene copies were obtained by cloning and then

The reservations about safety of retroviral vectors is sought to be solved by developing suicide vectors, which can not replicate after delivery of the gene.The second approach is the direct injection of DNA into the tissues either as protein complexes or even as naked DNA into muscle or skin.

Interestingly, these cells take up the DNA and express the gene product. Exciting results have been obtained with experimental familial hypercholesterolemia, where LDL receptor levels have been augmented by injection of the gene as a sialoglycoprotein complex.