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Cone rod dystrophies.

Hamel CP - Orphanet J Rare Dis (2007)

Bottom Line: At end stage, however, CRDs do not differ from RCDs.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.

View Article: PubMed Central - HTML - PubMed

Affiliation: 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. hamel@montp.inserm.fr

ABSTRACT
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.

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Fundus of a 45 year-old patient with cone rod dystrophy segregating with a loss-of-function mutation (E1087X) in ABCA4. Note the presence of various-shaped pigment deposits in the posterior pole with atrophy of the retina, while the retina appears less damaged in periphery (upper part of the photograph).
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Figure 1: Fundus of a 45 year-old patient with cone rod dystrophy segregating with a loss-of-function mutation (E1087X) in ABCA4. Note the presence of various-shaped pigment deposits in the posterior pole with atrophy of the retina, while the retina appears less damaged in periphery (upper part of the photograph).

Mentions: In the first stage, the main symptom is decreased visual acuity, which is usually discovered at school, in the first decade of life, and which does not significantly improve with spectacles. Patients often have a noticeable deviated gaze to project images on parafoveal regions of their retina that are less damaged. Along with this symptom, there are intense photophobia and a variable degree of dyschromatopsia. In contrast, night blindness is not mentioned by patients or, when present, is never as prominent as the decrease in visual acuity. Visual field testing shows central scotomas, while periphery is spared. As a result, patients have no difficulties to move. Fundus examination shows pigment deposits and various degrees of retinal atrophy in the macular region (Figure 1). Retinal vessels are usually normal or moderately attenuated. The optic disc is often pale at early stages, particularly on the temporal side, which accounts for the macular fibre bundle. At this stage, the question is to differentiate CRDs from macular dystrophies such as Stargardt disease, cone dystrophies and other rare macular conditions. Additional investigations help the diagnosis. First, fluorescein angiography and fundus autofluorescence show that the peripheral retina is also involved with heterogeneity in the fluorescence, but to a lesser extent than the macula. Second, the electroretinogram (ERG) shows a shift in implicit time of cone responses, followed by a decrease in both cone and rod responses. Cone responses are more severely affected than rod responses.


Cone rod dystrophies.

Hamel CP - Orphanet J Rare Dis (2007)

Fundus of a 45 year-old patient with cone rod dystrophy segregating with a loss-of-function mutation (E1087X) in ABCA4. Note the presence of various-shaped pigment deposits in the posterior pole with atrophy of the retina, while the retina appears less damaged in periphery (upper part of the photograph).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC1808442&req=5

Figure 1: Fundus of a 45 year-old patient with cone rod dystrophy segregating with a loss-of-function mutation (E1087X) in ABCA4. Note the presence of various-shaped pigment deposits in the posterior pole with atrophy of the retina, while the retina appears less damaged in periphery (upper part of the photograph).
Mentions: In the first stage, the main symptom is decreased visual acuity, which is usually discovered at school, in the first decade of life, and which does not significantly improve with spectacles. Patients often have a noticeable deviated gaze to project images on parafoveal regions of their retina that are less damaged. Along with this symptom, there are intense photophobia and a variable degree of dyschromatopsia. In contrast, night blindness is not mentioned by patients or, when present, is never as prominent as the decrease in visual acuity. Visual field testing shows central scotomas, while periphery is spared. As a result, patients have no difficulties to move. Fundus examination shows pigment deposits and various degrees of retinal atrophy in the macular region (Figure 1). Retinal vessels are usually normal or moderately attenuated. The optic disc is often pale at early stages, particularly on the temporal side, which accounts for the macular fibre bundle. At this stage, the question is to differentiate CRDs from macular dystrophies such as Stargardt disease, cone dystrophies and other rare macular conditions. Additional investigations help the diagnosis. First, fluorescein angiography and fundus autofluorescence show that the peripheral retina is also involved with heterogeneity in the fluorescence, but to a lesser extent than the macula. Second, the electroretinogram (ERG) shows a shift in implicit time of cone responses, followed by a decrease in both cone and rod responses. Cone responses are more severely affected than rod responses.

Bottom Line: At end stage, however, CRDs do not differ from RCDs.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.

View Article: PubMed Central - HTML - PubMed

Affiliation: 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. hamel@montp.inserm.fr

ABSTRACT
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.

Show MeSH
Related in: MedlinePlus