The are two catergories of gene therapy, somatic gene therapy and germline gene therapy. Somatic gene therapy alters the gene in a certain type of cell in patient. The process is only used on patients after fertilisation and the process is not permanent and will not be inherited by the next generation. Germline gene therapy is perform on the gametes (sex cells) and will only affect the child. This procedure is permanent and is hereditary.
The germline gene therapy process requires healthy donor cells to transfer the altered nucleus into. Scientists use lasers to puncture of the cell membrane then using high velocity tungsten microprojectiles to insert the correct genome into the nucleus. Everything else is then discarded and the nucleus, which contains the DNA of the patient couple is then inserted into the donor egg after having its nucleus removed as well. The window of opportunity in altering a gene only occurs when a cell is quicesent. During this time the chromosome of development mechanisims can be reprogramed. As shown in the example, the faulty part was not in the cell but rather in the mitochondria, but this process can also be used to change the genome of the nucleus which contains the DNA.
Somatic gene therapy require the use of viruses to infect and spead the new gemone throughout the body. Because viruses release chemicals similar to the natural cells drom the body, viruses are able to tick the body into beliving that the is no foreign element within the body. Otherwise the body's immune system will kill off the virus before it could spead the genes. Scientists use lasers to puncture the cell membrane and insert the healed gene into the RNA within the virus cell(1). RNA is the chemical which tells what cells to do(2), so by manipulating that process scientists are able to heal genetic disorders(3). The healed cells will now continue to multiply and affect other cells(4).