What is gene therapy?
This page is a general introduction to what gene therapy is and how it is used today by medical professionals.
What is Gene Therapy?
Gene therapy is a technique used by scientists that modifies someone's genes by changing their genetic code to treat and cure diseases, this is instead of using drugs or carrying out a surgery.
There are several ways that gene therapy can be carried out. Earlier methods of gene therapy included introducing a new gene into a cell that helped to fight a specific disease or introducing a non-faulty gene into the genetic code to 'stand in' for the gene that was causing the specific disease.
Different methods of gene therapy have since been developed. One method is referred to as 'genome editing' this is where you alter existing DNA in the cell with molecular tools. Genome editing can achieve a variety of different things. It can turn on a gene to help fight a disease, it can turn off a gene that is causing a disease. It can also fix an alteration in the genetic code that underlies a disorder. Finally it can remove pieces of DNA that are causing disorders.
Gene therapy can only help a small amount of diseases however with new methods such as 'genome editing' there should be more diseases it can help with in the future.
Gene Therapy Methods
Currently gene therapy treatments may be divided into the following four categories:
-Gene Augmentation- This type of treatment is used to treat diseases that are caused by 'loss of function mutations' . This means that the gene cannot produce a functioning product. This type of gene therapy introduces new DNA which replaces the lost gene, so that a functioning product can be produced at sufficient levels. Gene augmentation is the most commonly used treatment for spinal muscular atrophy.
-Gene silencing- This type of gene therapy is used when adding an additional gene does not change the phenotype of the gene. This type of gene treatment is where the abnormal gene that is causing the disease is shut down.
-Gene suicide - This type of gene therapy is also known as virus-directed enzyme prodrug therapy, this is where 'suicide genes' are introduced into tumour cells in a targeted manner. These genes produces toxic products in the tumour cells which causes them to die.
-Gene editing - Gene editing has been made a lot more easier and economical in recent years and there are different ways that gene editing is carried out. One way being where the treatment inhibits a pathogenic gene and another being where a gene is corrected by single base pairing.
When choosing what type of gene therapy is appropriate for a particular genetic defect you must take into consideration the status of the genetic defect. A defect can be described in two ways, a disease which will cause a person to die early or suffer greatly or something that stunts someone's future development.
Types of Therapy
-Negative therapy- removal of defects of diseases by selection
-Positive therapy- The enhancement or improvement of human qualities by alteration of certain genes
Two ways in which genes may be engineered:
-Passive control- couples being tested prior to having a child for genetic counselling which encourages them not to have a child if it is likely they will be born with a severe genetic defect or to have an abortion and use IVF treatment.
Active control - either somatic gene cell therapy ( where there is a direct interference where there is either an addition or alteration to the genes which changes its characteristics, however this does not modify future generations )or germ line gene cell therapy (alteration or addition of gametes this causes future generation to be modified as well )
For active negative therapy the aim is to replace the abnormal gene with a normal one at the same site as the chromosome.