Genes are sequences of DNA that code for the proteins in our bodies. Genetic diseases are mostly caused by mutations in a person’s DNA, which affect the quality or amount of a particular protein that is being produced.
To correct a genetic disease, the idea of gene therapy is to use normal, healthy genes as medicine as a way to bypass the genetic cause of the disease. For example, where a patient’s genetic disease is caused by too little of a particular protein, gene therapy may be used to increase the amount of protein in the body.
There are several ways in which genes can be introduced into cells. Examples include:
- individually, cell by cell
- shot through the cell membrane of cells
- the use of an electrical charge to make the cell membrane “leaky,” enabling the gene/DNA to pass into a cell.
None of these methods are very efficient, so instead we use defective, or “disarmed” viruses as a means to transport genes/DNA into the cells of interest.
One of the viruses used for gene delivery is called adeno-associated virus (AAV). It is a virus that is not known to cause any diseases in humans. In some cases it can stay inside a cell and express a gene for a long time. The AAV virus vector can also genetically modify many different types of cells. Defective AAV virus can efficiently deliver genes to the liver.
The Gene Therapy Research Unit
is now preparing for human clinical trials of an AAV-based treatment for inherited liver disease (OTC-deficiency).
AAV may be a safer and more effective alternative to liver transplantation, which is the only current treatment for some children.
The Gene Therapy Research Unit was the first group in Australia to treat a genetic disease, (SCID-X1, a rare immune deficiency disorder) by gene therapy. X-linked severe combined immunodeficiency (SCID-X1) is a rare immune deficiency disorder and is caused by mutations in a gene called gamma C (the common gamma chain of several interleukin receptors). Affected infants often have an immune system that does not work properly, most lack immune cells called T and natural killer (NK) cells and they have abnormal B cells. As a result, children suffer life-threatening problems fighting infections. Some people call this the “boy-in-the-bubble” disease, because in some countries patients are placed in isolation to stop them from getting infections.