Gene therapy

Gene therapy is an experimental technique that uses genes to treat or prevent disease. In the future, this technique may allow doctors to treat a disorder by inserting a gene into a patient’s cells instead of using drugs or surgery.

Why should I be aware of this?

Gene therapy has the potential to treat a number of diseases (including inherited disorders, some types of cancer, and certain viral infections). However, the technique is still under study and remains risky until research proves it will be safe and effective. Gene therapy is currently only being tested for the treatment of diseases that have no other cures.

Approaches being tested for gene therapy include:

• Replacing a mutated gene that causes disease with a healthy copy of the gene.
• Inactivating, or eliminating a mutated gene that is not functioning properly.
• Introducing a new gene into the body to help fight a disease.

All about gene therapy

In gene therapy the process involves inserting a "normal" gene into the genome to replace an "abnormal," disease-causing gene. The therapeutic gene is inserted to the patient's target cells with a carrier molecule called a vector. Currently, the most common vector is a virus that has been genetically altered to carry normal human DNA. Viruses have evolved a way of encapsulating and delivering their genes to human cells in a pathogenic manner. Scientists use this capability to manipulate the virus genome to remove disease-causing genes and insert therapeutic genes.

Viruses used

The following are some of the different types of viruses used as gene therapy vectors:

• Retroviruses - A class of viruses that can create double-stranded DNA copies of their RNA genomes. These copies of its genome can be integrated into the chromosomes of host cells. Human immunodeficiency virus (HIV) is a retrovirus.
• Adenoviruses - A class of viruses with double-stranded DNA genomes that cause respiratory, intestinal, and eye infections in humans. The virus that causes the common cold is an adenovirus.
• Adeno-associated viruses - A class of small, single-stranded DNA viruses that can insert their genetic material at a specific site on chromosome 19.
• Herpes simplex viruses - A class of double-stranded DNA viruses that infect a particular cell type, neurons. Herpes simplex virus type 1 is a common human pathogen that causes cold sores.

Non-viral options

There are also several non-viral options for gene delivery, the simplest being the direct introduction of therapeutic DNA into target cells. However, this approach can be used only with certain tissues and requires large amounts of DNA.

Creation of an artificial lipid sphere with an aqueous core is another non-viral approach. This liposome, which carries the therapeutic DNA, is capable of passing the DNA through the target cell's membrane.

Experiments into introduction of a 47th (artificial human) chromosome into target cells are also under way. This chromosome would exist autonomously alongside the standard 46 --not affecting their workings or causing any mutations. It would be a large vector capable of carrying substantial amounts of genetic code, and scientists anticipate that, because of its construction and autonomy, the body's immune systems would not attack it. A problem with this potential method is the difficulty in delivering such a large molecule to the nucleus of a target cell.

Current status

No human gene therapy product has so far been approved by the US Food and Drug Administration (FDA). The therapy is still in experimental stage and has not proven very successful in clinical trials and little progress has been made since the first gene therapy clinical trial began in 1990.

CopperBytes

• Many diseases cannot be cured with the typical medical methods available today.
• Great hope exists that it will be possible in the future to provide long-term treatment for inherited disease as well as chronic diseases and some forms of cancer with gene therapy.

90 degrees

Researchers reported in the New England Journal of Medicine that the technique cured eight of 10 children suffering from usually lethal "bubble boy disease," a lack of immunity that leaves children vulnerable to infections. After two to eight years, all the patients were alive, unlike a previous trial.

That came on top of an announcement last year that two groups of researchers independently used gene therapy to treat a form of hereditary blindness in a small number of patients, restoring some vision. The evidence, also published in the New England Journal, was presented at a scientific conference in April.

References:

• What is gene therapy?
• Gene Therapy