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Choroideremia (CHD) is a rare X-linked recessive inherited disorder giving rise to retinal disease and eventual blindness, resulting from degeneration of the choriocapillaris of the choroid and of the retinal pigment epithelium of the retina. The disease results in progressive loss of vision, almost exclusively in males; in childhood, night blindness is the most common first symptom. As the disease progresses, vision loss results, frequently starting as an irregular ring that gradually expands both in toward central vision and out toward the extreme periphery; progression continues throughout the individual's life, where both the rate of change and the degree of visual loss are variable among those affected, even within the same family. The affected tissues include the ''retinal pigment epithelium'' (RPE), which is the pigmented cell layer just outside the neurosensory retina that nourishes retinal visual cells; the RPE overlies the retinal visual cells and is firmly attached to the underlying choroid,〔 where degeneration of the ''capillary lamina of choroid'' (choriocapillaris) is also observed. Photoreceptors of the RPE convert light into the electrical impulses that are transferred to the brain, where the images seen as a result are constructed; the vessels of the choriocapillaris provide oxygen and nutrients to the RPE and photoreceptor cells. In the early stages of CHD, the choroid and the retinal pigment epithelium begin to deteriorate, after which loss of photoreceptor occurs, leading to loss of vision. At a molecular level, the root cause of the disease is mutation leading to loss of a specific Rab escort protein 1 (REP1), which, with its partner REP2, are responsible for prenylation of Rab proteins, where the link between the build up of unprenylated Rab proteins and the developing blindness is not yet known. Medical approaches to the disease have resulted in the application of a diagnostic test for CHD, and 2014 saw the onset of clinical trials for gene therapies using viral vector-borne RP1 gene constructs aimed at protection of cells not yet lost to the disease. In these early clinical studies, patients have consistently shown improvements during the course of study; persistence data are in the process of being gathered. ==Pathophysiology and presentation== Choroideremia is caused by the deletion of the Rab escort protein 1 (REP1). Rab escort protein 2 (REP2) is 75% identical and can to an extent compensate for the loss of REP1. Though the eye does express the REP2 protein (no cell could survive without some REP activity) evidently, in the eye, this is not enough. The REPs are essential for the prenylation of Rab proteins. Studies have shown that there is a build up of unprenylated Rab27 in lymphoblasts from Choroideremia patients. The link between the build up of unprenylated Rab proteins and blindness is not known. Generally, only males show symptoms of this disease. Initially a person suffering from choroideremia has night blindness, which begins in youth. As the disease progresses, a CHM sufferer loses their peripheral vision and depth perception, eventually losing all sight by middle age. In some cases, a severe loss of acuity and color perception become evident as the disease progresses. 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「choroideremia」の詳細全文を読む スポンサード リンク
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