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Gene therapy for color blindness is an experimental gene therapy aiming to convert congenitally colorblind individuals to trichromats by introducing a photopigment gene that they lack. Though partial color blindness is considered only a mild disability and is controversial whether it is even a disorder, it is a condition that affects many people, particularly males. Complete color blindness, or achromatopsia, is very rare but more severe. While never demonstrated in humans, animal studies have shown that it is possible to confer color vision by injecting a gene of the missing photopigment using gene therapy. As of 2014 there is no medical entity offering this treatment, and no clinical trials available for volunteers. ==Color Blindness== (詳細はretina of the human eye contains photoreceptive cells called cones that allow color vision. A normal trichromat individual possesses three different types of cones to distinguish different colors within the visible spectrum from 380 nm to 740 nm. The three types of cones are designated L, M, and S cones, and each type is sensitive to a certain range of wavelength of light depending on what photopigment it contains. More specifically, the L cone absorbs around 560 nm, the M cone absorbs near 530 nm, and the S cone absorbs near 420 nm.〔 Contrary to popular belief, the peak absorption frequency for L, M, and S cones do not exactly correspond to red, green, and blue wavelength. Rather, the peak frequency for the L cone is orange, yellowish green in M cones, and blue-violet in S cones. These cones transduce the absorbed light into electrical information to be relayed to neurons in the retina such as retinal bipolar cells and retinal ganglion cells, before reaching the brain.〔 The signals from different cones are added or subtracted from each other to process the color of incoming light. For instance, the color red stimulate L cones more than M cones, whereas the color green stimulates the L and M cones more than the S cones.〔 The colors are perceived in an opponent process, such that red and green are perceived in opposition, as are blue and yellow, black and white.〔 The gene loci coding for the photopigments: M-opsin and L-opsin are located in close proximity within the X chromosome and are highly polymorphic.〔 Among the population, some have a deleted gene for the M photopigment in the X chromosome (such as in deuteranopia), whereas others have a mutated form of the gene (such as in deuteranomaly). Individuals who can express only two types of opsins in the cones are called dichromats. Because males have only one copy of the X chromosome, dichromatism is much more prevalent among men.〔 With only two types of cones, dichromats are less capable of distinguishing between two colors. In the most common form of color blindness, deuteranopes have difficulty discriminating between red and green color.〔 This is shown by their poor performance in Ishihara test. Although dichromatism poses little problem for daily life, dichromats may find some color-coded diagrams and maps difficult to read. Less common forms of dichromacy include protoanopia (lack of L-cones), and tritanopia (lack of S-cones). If a person lacks two types of photopigments, they are considered monochromats. People lacking the three types of photopigments are said to have complete color blindness or achromatopsia. Color blindness can also result from damages to the visual cortex in the brain.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Gene therapy for color blindness」の詳細全文を読む スポンサード リンク
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