Absorption of a photon by an opsin pigment causes isomerization of the chromophore from 11-cis-retinaldehyde to all-trans-retinaldehyde. Regeneration of visual chromophore following light exposure is dependent on an enzyme pathway called the retinoid or visual cycle. Our understanding of this pathway has been greatly facilitated by the identification of disease-causing mutations in the genes coding for visual cycle enzymes. Defects in nearly every step of this pathway are responsible for human-inherited retinal dystrophies. These retinal dystrophies can be divided into two etiologic groups. One involves the impaired synthesis of visual chromophore. The second involves accumulation of cytotoxic products derived from all-trans-retinaldehyde. Gene therapy has been successfully used in animal models of these diseases to rescue the function of enzymes involved in chromophore regeneration, restoring vision. Dystrophies resulting from impaired chromophore synthesis can also be treated by supplementation with a chromophore analog. Dystrophies resulting from the accumulation of toxic pigments can be treated pharmacologically by inhibiting the visual cycle, or limiting the supply of vitamin A to the eyes. Recent progress in both areas provides hope that multiple inherited retinal diseases will soon be treated by pharmaceutical intervention.

中文翻译：

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视觉周期缺陷引起的疾病：类视黄醇作为潜在的治疗剂。

视蛋白色素吸收光子会导致生色团从11-顺式-视黄醛异构化为全反式-视黄醛。曝光后视觉发色团的再生取决于称为维甲酸或视觉周期的酶途径。鉴定视觉循环酶基因的致病突变大大促进了我们对该途径的理解。该途径几乎每个步骤中的缺陷都与人类遗传性视网膜营养不良有关。这些视网膜营养不良可分为两个病因学组。一种涉及视觉发色团的合成受损。第二个涉及从全反式维甲酸醛衍生的细胞毒性产物的积累。基因疗法已成功用于这些疾病的动物模型中，以恢复参与生色团再生的酶的功能，恢复视力。由发色团合成受损引起的营养不良也可以通过补充发色团类似物来治疗。可以通过抑制视觉周期或限制对眼睛的维生素A供给，从药理上治疗有毒色素积聚引起的营养不良。这两个领域的最新进展都给人们带来希望，即将通过药物干预治疗多种遗传性视网膜疾病。可以通过抑制视觉周期或限制对眼睛的维生素A供给，从药理上治疗有毒色素积聚引起的营养不良。这两个领域的最新进展都给人们带来希望，即将通过药物干预治疗多种遗传性视网膜疾病。可以通过抑制视觉周期或限制对眼睛的维生素A的供应，在药理上治疗由有毒色素积累引起的营养不良。这两个领域的最新进展都给人们带来希望，即将通过药物干预治疗多种遗传性视网膜疾病。