Human beings suffer from more than 5000 different diseases caused by single gene mutations, e.g., cystic fibrosis acatalasis, hunting tons chorea, tay sachs disease, lisch nyhan syndrome, sickle cell anemia, mitral stenosis, hunter's syndrome, haemophilia, several forms of muscular dystrophy etc. In addition, many common disorders like cancer, hypertension, atherosclerosis and mental illness seem to have genetic components.
The term gene therapy can be defined as introduction of a normal functional gene into cells, which contain the defective allele of concerned gene with the objective of correcting a genetic disorder or an acquired disorder.
The first approach in gene therapy is: -
a) Identification of the gene that plays the key role in the development of a genetic disorder.
b) Determination of the role of its product in health and disease.
c) Isolation and cloning of the gene.
d) Development of an approach for gene therapy.
The genetic material may be transferred directly into cells within a patient, which is referred as in vivo gene therapy or else cells may be removed from the patient and the genetic material inserted into them, which is referred as invitro gene therapy. Apart from the two methods mentioned above there is one more method that is ex-vivo gene therapy in which genetic material is inserted into the cells just prior to transplanting the modified cells back into the patient.
Major disease classes under gene therapy include: -
a) Infectious diseases: - infection by a virus or bacterial pathogen
b) Cancers: - uncontrolled and enormous cell division and cell proliferation as a result of activation of an oncogene or inactivation of a tumors suppressor gene or an apoptosis gene.
c) Inherited disorders: - genetic deficiency of an individual gene product or genetically determined in appropriate expression of a gene.
d) Immune system disorders: - includes allergies, inflammation and also autoimmune diseases in which immune system cells appropriately destroy body cells.