Human genetic engineering is the alteration of an individual's genotype with the aim of choosing the phenotype of a newborn or changing the existing phenotype of a child or adult.[1]

It holds the promise of curing genetic diseases like cystic fibrosis. Gene therapy has been successfully used to treat multiple diseases, including X-linked SCID,[2]chronic lymphocytic leukemia (CLL),[3] and Parkinson's disease.[4] In 2012, Glybera became the first gene therapy treatment to be approved for clinical use in either Europe or the United States after its endorsement by the European Commission.[5][6]

It is speculated that genetic engineering could be used to change physical appearance, metabolism, and even improve physical capabilities and mental faculties like memory and intelligence, although for now these uses are limited to science fiction.

Gene therapy trials on humans began in 2004 on patients with severe combined immunodeficiency (SCID). In 2000, the first gene therapy "success" resulted in SCID patients with a functional immune system. These trials were stopped when it was discovered that two of ten patients in one trial had developed leukemia resulting from the insertion of the gene-carrying retrovirus near an oncogene. In 2007, four of the ten patients had developed leukemia.[7] Work is now focusing on correcting the gene without triggering an oncogene. Since 1999, gene therapy has restored the immune systems of at least 17 children with two forms (ADA-SCID and X-SCID) of the disorder.[citation needed]

Human genetic engineering is already being used on a small scale to allow infertile women with genetic defects in their mitochondria to have children.[8] The technique, known as ooplasmic transfer, is used to inject the mitochondria from the donor's egg cell into the egg of the infertile woman. In vitro fertilization is performed on the egg. [9] Healthy human eggs from a second mother are used. The first mother thus contributes the 23 chromosomes of the nuclear genome, which contain the majority of the child's genetic information, while the second mother contributes the mitochondrial genome, which contains 37 genes. The child produced this way has genetic information from two mothers and one father.[8] The changes made are germline changes and will likely be passed down from generation to generation, and, thus, are a permanent change to the human genome.[8]

Other forms of human genetic engineering are still theoretical. Recombinant DNA research is usually performed to study gene expression and various human diseases. This includes the creation of transgenic animals, such as mice.

Genetic engineering can be broken down into two applications, somatic and germline. Both processes involve changing the genes in a cell through the use of a vector carrying the gene of interest. The new gene may be integrated into the cells genetic material through recombination, or may remain separate from the genome, such as in the form of a plasmid. If integrated into the genome, it may recombine at a random location or at a specific location (site-specific recombination) depending on the technology used.

As the name suggests, somatic cell therapy alters the genome of somatic cells. This process targets specific organs and tissues in a person. The aim of this technique is to correct a mutation or provide a new function in human cells. If successful, somatic cell therapy has the potential to treat genetic disorders with few therapeutic options. This process does not affect the genetics of gametic cells within the same body. Any genetic modifications are restricted to a patient individually and cannot be passed on to their offspring.

Several somatic cell gene transfer experiments are currently in clinical trials with varied success. Over 600 clinical trials utilizing somatic cell therapy are underway in the United States. Most of these trials focus on treating severe genetic disorders, including immunodeficiencies, haemophilia, thalassaemia, and cystic fibrosis. These disorders are good candidates for somatic cell therapy because they are caused by single gene defects. While somatic cell therapy is promising for treatment, a complete correction of a genetic disorder or the replacement of multiple genes in somatic cells is not yet possible. Only a few of the many clinical tries are in the advanced stages.[10]

Germline cell therapy alters the genome of germinal cells. Specifically, it targets eggs, sperm, and very early embryos. Genetic changes made to germline cells affect every cell in the resulting individuals body and can also be passed on to their offspring. The practice of germline cell therapy is currently banned in several countries, but has not been banned in the US.

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Human genetic engineering - Wikipedia, the free encyclopedia

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