Gene therapy is the fairly new method of disease treatment aimed mostly at genetic diseases. Basically, a normal allele is inserted into a patient's defective cells. This is a very new approach and most gene therapy is aimed at cancer treatment and hereditary genetic diseases, such as sickle cell anemia, cystic fibrosis, and muscular dystrophy. These particular genetic diseases are caused by defects in single genes. Scientists can modify DNA in bacteria fairly easily, however, they have had more trouble trying to modify human DNA because the human genome is much more complex. There are also ethical concerns with using gene therapy that limit it's use on humans.
There are 2 main types of gene therapy. They are germ line gene therapy and somatic gene therapy. Germ line gene therapy deals with trying to modify the DNA in a patient's germ cells (eggs or sperm). They focus on what is passed to the patient's offspring. Somatic gene therapy just treats the patient's other cells and does not have an effect on the patient's offspring.
If a child or an embryo(fetus) is diagnosed to carry a defective gene leading to disability,one may like to correct this defect by any of the three methods:1)by replacement of defective gene with a normal gene.2) by correcting the defective gene through gene targeting or 3) by gene augmentation either through increasing the number of copies of the gene or through a higher level of expression of the introduced gene.Such a correction of a genetic defect is described as gene therapy.Gene therapy can be used at two different levels:1) embryo therapy,in which the genectic constitution of embryo at the post zygotic level is altered,so that the inheritance will also be altered.and 2) patient therapy,in which cells with healthy gene may be introduced in the affected tissue,so that the healthy gene overcomes the defect without affecting the inheritance of the patient.In recent years,approved gene therapy experiments have been conducted.These examples are as follows:1) Neo R/TIL gene marking.2) ADA gene therapy.3) cancer gene therapy