Gene Therapy

Gene therapy is the treatment of a genetic disorder by inserting a functional allele into a patient's cells, so that the cells can make the protein that the faulty allele fails to produce. It is best suited to disorders caused by a single recessive allele, such as cystic fibrosis or severe combined immunodeficiency (SCID).In somatic cell gene therapy the healthy allele is inserted into body cells, such as the epithelial cells lining the airways or bone marrow stem cells. Only the treated person is affected and the allele is not passed on to their children. The treated cells are eventually replaced, so the treatment often has to be repeated.In germ line gene therapy the allele is inserted into gametes or an early embryo. Every cell of the resulting individual carries the functional allele and it can be inherited by future generations. Germ line therapy in humans is illegal in the UK because of ethical concerns and unknown effects on future generations.The allele is delivered by a vector. Modified viruses such as adenoviruses and retroviruses, with their harmful genes removed, can carry the allele into host cells. Liposomes, small spheres of phospholipid, can fuse with cell surface membranes and carry the DNA inside.Problems include immune responses against the vector, the allele being expressed for only a short time, and viral vectors inserting the allele at random places in the genome, which can disrupt other genes and has caused cancer in some patients. Successes include treatments for SCID and some inherited forms of blindness.