Cone-rod dystrophy (CORD) and retinitis pigmentosa (RP) are clinically and genetically overlapping heterogeneous retinal dystrophies. RP is characterized initially by rod photoreceptor dysfunction, giving rise to night blindness, which is followed by progressive rod and cone photoreceptor dystrophy, ... Cone-rod dystrophy (CORD) and retinitis pigmentosa (RP) are clinically and genetically overlapping heterogeneous retinal dystrophies. RP is characterized initially by rod photoreceptor dysfunction, giving rise to night blindness, which is followed by progressive rod and cone photoreceptor dystrophy, resulting in midperipheral vision loss, tunnel vision, and sometimes blindness. In contrast to RP, CORD is characterized by a primary loss of cone photoreceptors and subsequent or simultaneous loss of rod photoreceptors. The disease in most cases becomes apparent during primary-school years, and symptoms include photoaversion, decrease in visual acuity with or without nystagmus, color vision defects, and decreased sensitivity of the central visual field. Because rods are also involved, night blindness and peripheral vision loss can occur. The diagnosis of CORD is mainly based on electroretinogram (ERG) recordings, in which cone responses are more severely reduced than, or equally as reduced as rod responses (summary by Estrada-Cuzcano et al., 2012).
Estrada-Cuzcano et al. (2012) studied 4 unrelated consanguineous families with retinal dystrophy. Four patients from 2 families were diagnosed with cone-rod dystrophy, and 2 patients from 2 families were diagnosed with retinitis pigmentosa with early macular involvement. Age ... Estrada-Cuzcano et al. (2012) studied 4 unrelated consanguineous families with retinal dystrophy. Four patients from 2 families were diagnosed with cone-rod dystrophy, and 2 patients from 2 families were diagnosed with retinitis pigmentosa with early macular involvement. Age at presentation ranged from infancy to late teens. The patients all showed early involvement of the macula, resulting in loss of central vision at an early age: none had visual acuity better than 20/60 and 1 patient had light perception only. All showed attenuation of retinal vessels, and the CORD patients had temporal optic disc pallor and some pigment clumping, whereas the RP patients had bone spicule-like pigmentation and waxy optic disc. Rod and cone patterns were nonrecordable by electroretinography (ERG) in the 2 RP patients and in 2 of the CORD patients; in the other 2 CORD patients, the cone pattern was nonrecordable and the rod recording was severely reduced. A brother and sister with CORD also had postaxial polydactyly: each had an extra finger or toe on the right hand or foot, respectively.
In the proband from a consanguineous family, who had retinitis pigmentosa with early macular involvement, Estrada-Cuzcano et al. (2012) performed genomewide homozygosity mapping followed by targeted next-generation sequencing and identified a homozygous nonsense mutation in the C8ORF37 gene ... In the proband from a consanguineous family, who had retinitis pigmentosa with early macular involvement, Estrada-Cuzcano et al. (2012) performed genomewide homozygosity mapping followed by targeted next-generation sequencing and identified a homozygous nonsense mutation in the C8ORF37 gene (614477.0001) on chromosome 8q22.1. Analysis of C8ORF37 in 15 consanguineous families with retinal dystrophy revealed homozygosity for 1 splice site and 2 missense mutations in affected individuals from 3 families, respectively, 2 with cone-rod dystrophy (614477.0002; 614477.0003) and 1 with RP (614477.0004). Two affected sibs from 1 of the families also had postaxial polydactyly; Estrada-Cuzcano et al. (2012) noted that the Bardet-Biedl ciliopathy syndrome (209900) also includes both polydactyly and retinal dystrophy.