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CONE-ROD DYSTROPHY 7; CORD7

CONE-ROD DYSTROPHY 7; CORD7

Kelsell et al. (1998) described a 4-generation British family with autosomal dominant cone-rod dystrophy. Affected members first became aware of reduced color vi...

Kelsell et al. (1998) described a 4-generation British family with autosomal dominant cone-rod dystrophy. Affected members first became aware of reduced color vision and visual acuity between the ages of 20 and 40 years. As the disorder progressed, they reported difficulty seeing in bright light. At the onset of symptoms, retinal pigmentary changes were already present around the fovea, simulating a bull's eye dystrophy, and progressed to macular atrophy.

Michaelides et al. (2005) provided additional details of the phenotype in the family reported by Kelsell et al. (1998). The majority of affected individuals described a progressive deterioration of central vision, night vision, and peripheral visual field usually between the third and fourth decades. Visual acuity ranged from 6/6 to 3/60. Patients experienced mild photophobia and had no nystagmus. Mild to moderate generalized dyschromatopsia was detected in a majority of the patients. Fundus changes ranged from mild retinal pigment epithelial disturbance to extensive atrophy and pigmentation. An absent or severely reduced pattern ERG (PERG) was detected in all subjects, indicative of marked macular dysfunction. Full-field ERG revealed abnormal rod and cone responses. Fundus autofluorescence (AF) imaging showed decreased macular AF centrally surrounded by a ring of increased AF in a majority of affected individuals.

Kniazeva et al. (1999) examined 10 members of a 4-generation family segregating an autosomal dominant form of macular dystrophy and identified 5 individuals with characteristic features of cone-rod dystrophy and Stargardt disease; a sixth family member (deceased) was classified as affected by history. Most affected individuals had gradual onset of decreased visual acuity during the fourth decade, bilateral macular atrophy, diffusely abnormal ERG responses, and markedly reduced color vision. In addition, several affected individuals demonstrated features highly suggestive of Stargardt-like disease (see 248200), such as yellow 'flavimaculatus flecks' in the retinal pigment epithelium and a 'dark choroid' pattern on fluorescein angiography.

▼ Mapping
Kelsell et al. (1998) mapped a form of autosomal dominant cone-rod dystrophy to chromosome 6q in a 4-generation British family. Two-point linkage data for the family excluded the 6p12 region occupied by the gene encoding peripherin/RDS (PRPH2; 179605) and the 6q14-q16.2 region occupied by the genes for North Carolina macular dystrophy (MCDR1; 136550) and progressive bifocal chorioretinal atrophy (PBCRA; 600790). Haplotype analysis localized the disease-causing locus, designated CORD7, between D6S430 and D6S1625, a region estimated to be 7 cM. The IMPG1 gene (602870), a good functional candidate for retinal dystrophies, maps to the same region of chromosome 6 but was shown by Kelsell et al. (1998) to map telomeric to CORD7. An autosomal dominant Stargardt-like disease (STGD3; 600110) maps to the same region of chromosome 6 but is clinically distinct.

In a 4-generation family segregating autosomal dominant cone-rod dystrophy with features of Stargardt disease, Kniazeva et al. (1999) performed linkage analysis using DNA markers linked to known loci for cone-rod dystrophy and dominant Stargardt disease and obtained a maximum lod score of 3.3 (theta = 0.010) at marker D6S280 on chromosome 6q14. A recombination event in the family defined marker D6S284 as the telomeric marker for the genetic interval.

▼ Molecular Genetics
In 6 affected members of the 4-generation British family with CORD7, previously described by Kelsell et al. (1998), Johnson et al. (2003) identified heterozygosity for a missense mutation in the RIMS1 gene (606629.0001). The mutation was not found in 3 unaffected members of the family or in 115 ethnically matched controls. The authors stated that this was the first example of a mutation in a protein with a defined role in synaptic function giving rise to a retinal disease.

Tags: 6q13