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Cone rod dystrophy
Cone rod dystrophies (CRDs) are inherited retinal dystrophies that belong to the group of pigmentary retinopathies.
- Synonym(s): -
- Prevalence: 1-9 / 100 000
- Inheritance: Autosomal dominant or Autosomal recessive or X-linked recessive
- Age of onset: Childhood
- ICD-10: H35.5
- OMIM: 120970 300476 300834 303700 304020 600624 600977 601777 602093 603649 604116 604393 605549 608194 610283 610381 610478 612657 612775 613660 614500 615163 615374 615860 615973 616502
- UMLS: -
- MeSH: -
- GARD: 10790
- MedDRA: -
The prevalence of CRDs is estimated at 1 in 40,000.
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, explaining 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 nonsyndromic, but they may also be part of several syndromes, such as Bardet-Biedl syndrome (see this term) and Spinocerebellar Ataxia Type 7 (SCA7). Nonsyndromic 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 (see this term) 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.
he diagnosis of CRD is based on clinical history, fundus examination and electroretinogram. Molecular diagnosis can be made for some genes.
Genetic counseling is always advised.
Management and treatment
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.
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