Gene therapy is a method of treating, preventing, or curing a disease or medical condition by using a gene or genes. Gene therapies often works by replacing a damaged or missing gene in a patient's cells with a healthy form of that gene, or by adding new copies of a gene that is broken. Gene therapy has been used to treat both inherited genetic diseases (such as haemophilia and sickle cell disease) and acquired disorders (such as leukaemia). Ever since identification of the gene as the basic unit of heredity, the capacity to make site-specific alterations to the human genome has been a goal in medicine. As a result, gene therapy is defined as the ability to change one's genetic condition by correcting altered (mutated) genes or making site-specific modifications that target therapeutic treatment. This treatment was made possible by developments in genetics and bioengineering, which allowed for the manipulation of vectors to transfer extrachromosomal material to target cells. The optimization of delivery vehicles (vectors), which are primarily plasmids, nanostructured, or viruses, is one of the main foci of this technique. Viruses are studied more frequently because of their prowess at invading cells and inserting genetic material. However, heightened immunological responses and genetic alteration, particularly in germ line cells, are major concerns. In vivo investigations in somatic cells yielded positive results in clinical trials using approved methods.