Q.What is gene therapy ? Mention the two types of gene therapy.

Gene therapy corrects a hereditary disease by delivering a normal, functional copy of a gene, via a vector, into the cells of a patient carrying a mutant allele, so that the expressed normal gene product restores a normal phenotype; it has mainly targeted single-gene disorders like cystic fibrosis and haemophilia, for which no other effective treatment exists. Two strategies exist — gene augmentation therapy (adding a working gene copy) and gene inhibition therapy (silencing a harmful dominant gene with an antisense gene) — and two levels of application: somatic cell gene therapy (targeting non-reproductive cells like bone marrow, blood or skin; corrects the patient but is not inherited) and germline gene therapy (targeting eggs or sperm; heritable, and far more ethically contentious). The landmark case is ADA-deficiency SCID, first treated clinically by French Anderson in 1990 in a four-year-old girl: lymphocytes are drawn from the patient's blood, infected in culture with a disabled retrovirus carrying a working ADA gene, and reinfused; because these engineered cells are not immortal the patient needs periodic repeat infusions, and only introducing the corrected g …