Gene therapy By Shankar Gene therapy Gene therapy

Gene therapy By Shankar

Gene therapy • Gene therapy is when DNA is introduced into a patient to treat a genetic disease. The new DNA usually contains a functioning gene to correct the effects of a diseasecausing mutation. • Gene therapy is the insertion of genes into an individual's cells and tissues to treat a disease, and hereditary diseases in which a defective mutant allele is replaced with a functional one.

• Gene therapy uses sections of DNA (usually genes? ) to treat or prevent disease. • The DNA is carefully selected to correct the effect of a mutated gene that is causing disease. • The technique was first developed in 1972 but has, so far, had limited success in treating human diseases. • Gene therapy may be a promising treatment option for some genetic diseases? , dystrophy? and cystic fibrosis? . including muscular

Types • Somatic gene therapy: transfer of a section of DNA to any cell of the body that doesn’t produce sperm or eggs. Effects of gene therapy will not be passed onto the patient’s children. • Germline gene therapy: transfer of a section of DNA to cells that produce eggs or sperm. Effects of gene therapy will be passed onto the patient’s children and subsequent generations.

Gene therapy techniques There are several techniques for carrying out gene therapy. These include: • Gene augmentation therapy • Gene inhibition therapy • Killing of specific cells

Gene augmentation therapy • This is used to treat diseases caused by a mutation that stops a gene from producing a functioning product, such as a protein? . • This therapy adds DNA containing a functional version of the lost gene back into the cell. • The new gene produces a functioning product at sufficient levels to replace the protein that was originally missing. • This is only successful if the effects of the disease are reversible or have not resulted in lasting damage to the body.

Gene inhibition therapy • Suitable for the treatment of infectious diseases, cancer and inherited disease caused by inappropriate gene activity. • The aim is to introduce a gene whose product either: – inhibits the expression of another gene – interferes with the activity of the product of another gene. • The basis of this therapy is to eliminate the activity of a gene that encourages the growth of disease-related cells.

• For example, cancer is sometimes the result of the over-activation which stimulates of cell an oncogene (gene growth). So, by eliminating the activity of that oncogene through gene inhibition therapy, it is possible to prevent further cell growth and stop the cancer in its tracks.

Killing of specific cells • Suitable for diseases such as cancer that can be treated by destroying certain groups of cells. • The aim is to insert DNA into a diseased cell that causes that cell to die. • This can be achieved in one of two ways: – the inserted DNA contains a “suicide” gene that produces a highly toxic product which kills the diseased cell – the inserted DNA causes expression of a protein that marks the cells so that the diseased cells are attacked by the body’s natural immune system. • It is essential with this method that the inserted DNA is targeted appropriately to avoid the death of cells that are functioning normally.

DNA Transfer

Challenges of gene therapy • Delivering the gene to the right place and switching it on • Avoiding the immune response • Making sure the new gene doesn’t disrupt the function of other genes • The cost of gene therapy

Delivering the gene to the right place and switching it on • It is crucial that the new gene reaches the right cell • Delivering a gene into the wrong cell would be inefficient and could also cause health problems for the patient • Even once the right cell has been targeted the gene has to be turned on • Cells sometimes obstruct this process by shutting down genes that are showing unusual activity.

Avoiding the immune response • The role of the immune system is to fight off intruders. • Sometimes new genes introduced by gene therapy are considered potentially-harmful intruders. • This can spark an immune response in the patient, that could be harmful to them. • Scientists therefore have the challenge of finding a way to deliver genes without the immune system ‘noticing’. • This is usually by using vectors that are less likely to trigger an immune response.

Making sure the new gene doesn’t disrupt the function of other genes • Ideally, a new gene introduced by gene therapy will integrate itself into the genome of the patient and continue working for the rest of their lives. • There is a risk that the new gene will insert itself into the path of another gene, disrupting its activity. • This could have damaging effects, for example, if it interferes with an important gene involved in regulating cell division, it could result in cancer.

The cost of gene therapy • Many genetic disorders that can be targeted with gene therapy are extremely rare. • Gene therapy therefore often requires an individual, case-by-case approach. This may be effective, but may also be very expensive.