Hamel Christian P
Inserm U. 583, Physiopathologie et thérapie des déficits sensoriels et moteurs, Institut des Neurosciences de Montpellier, BP 74103, 80 av, Augustin Fliche, 34091 Montpellier Cedex 05, France.
Orphanet J Rare Dis. 2007 Feb 1;2:7. doi: 10.1186/1750-1172-2-7.
Cone rod dystrophies (CRDs) (prevalence 1/40,000) are inherited retinal dystrophies that belong to the group of pigmentary retinopathies. CRDs are characterized by retinal pigment deposits visible on fundus examination, predominantly localized to the macular region. In contrast to typical retinitis pigmentosa (RP), also called the rod cone dystrophies (RCDs) resulting from the primary loss in rod photoreceptors and later followed by the secondary loss in cone photoreceptors, CRDs reflect the opposite sequence of events. CRD is characterized by primary cone involvement, or, sometimes, by concomitant loss of both cones and rods that explains the predominant symptoms of CRDs: decreased visual acuity, color vision defects, photoaversion and decreased sensitivity in the central visual field, later followed by progressive loss in peripheral vision and night blindness. The clinical course of CRDs is generally more severe and rapid than that of RCDs, leading to earlier legal blindness and disability. At end stage, however, CRDs do not differ from RCDs. CRDs are most frequently non syndromic, but they may also be part of several syndromes, such as Bardet Biedl syndrome and Spinocerebellar Ataxia Type 7 (SCA7). Non syndromic CRDs are genetically heterogeneous (ten cloned genes and three loci have been identified so far). The four major causative genes involved in the pathogenesis of CRDs are ABCA4 (which causes Stargardt disease and also 30 to 60% of autosomal recessive CRDs), CRX and GUCY2D (which are responsible for many reported cases of autosomal dominant CRDs), and RPGR (which causes about 2/3 of X-linked RP and also an undetermined percentage of X-linked CRDs). It is likely that highly deleterious mutations in genes that otherwise cause RP or macular dystrophy may also lead to CRDs. The diagnosis of CRDs is based on clinical history, fundus examination and electroretinogram. Molecular diagnosis can be made for some genes, genetic counseling is always advised. Currently, there is no therapy that stops the evolution of the disease or restores the vision, and the visual prognosis is poor. Management aims at slowing down the degenerative process, treating the complications and helping patients to cope with the social and psychological impact of blindness.
锥体-杆体营养不良(CRDs)(患病率为1/40,000)是遗传性视网膜营养不良,属于色素性视网膜病变组。CRDs的特征是眼底检查可见视网膜色素沉着,主要局限于黄斑区。与典型的视网膜色素变性(RP)相反,RP也称为杆体-锥体营养不良(RCDs),由杆体光感受器原发性丧失,随后锥体光感受器继发性丧失引起,而CRDs反映的是相反的事件顺序。CRD的特征是原发性锥体受累,或者有时是锥体和杆体同时丧失,这解释了CRDs的主要症状:视力下降、色觉缺陷、畏光和中心视野敏感度降低,随后是周边视力逐渐丧失和夜盲。CRDs的临床病程通常比RCDs更严重、更迅速,导致更早出现法定失明和残疾。然而,在疾病末期,CRDs与RCDs并无差异。CRDs最常见的是非综合征性的,但它们也可能是几种综合征的一部分,如巴德-比德尔综合征和7型脊髓小脑共济失调(SCA7)。非综合征性CRDs在遗传上具有异质性(到目前为止已鉴定出10个克隆基因和3个基因座)。参与CRDs发病机制的四个主要致病基因是ABCA4(它导致斯塔加特病,也导致30%至60%的常染色体隐性CRDs)、CRX和GUCY2D(它们导致许多常染色体显性CRDs的报道病例)以及RPGR(它导致约2/3的X连锁RP,也导致未确定比例的X连锁CRDs)。在其他情况下导致RP或黄斑营养不良的基因中,高度有害的突变也可能导致CRDs。CRDs的诊断基于临床病史、眼底检查和视网膜电图。对于某些基因可以进行分子诊断,始终建议进行遗传咨询。目前,没有能够阻止疾病进展或恢复视力的治疗方法,视觉预后很差。治疗的目标是减缓退行性过程、治疗并发症并帮助患者应对失明带来的社会和心理影响。