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PubMed1997

Localisation of a gene for dominant cone-rod dystrophy (CORD6) to chromosome 17p.

We have performed genetic linkage analysis on a four generation British family with cone-rod dystrophy. Significant linkage to the disease gene was obtained with eight marker loci situated on chromosome 17p12-p13. A maximum two-point lod score of 5.93 with no recombination was obtained with marker locus D17S1844. Critical recombinants identified with flanking marker loci placed the disease gene between D17S796/D17S938 and D17S954, an interval estimated to be 8 cM in size. This new localisation for autosomal dominant cone-rod dystrophy (CORD6) overlaps with regions attributed previously to Leber's congenital amaurosis, central areolar choroidal dystrophy and dominant cone dystrophy. Given their differences in phenotype, the most plausible explanation would be that these different retinal disorders are caused by mutations in different genes mapping close together within the genome.

Chromosome Mapping↗

PubMed2001

Clinical features and a follow-up study in a family with X-linked progressive cone-rod dystrophy.

PURPOSE: To study a large family with X-linked progressive cone-rod dystrophy. METHODS: There were 128 members in the family. Of these, 45 had an ophthalmological examination and 3 gave their permission to use the results of their recent ophthalmological examination. In addition to the usual eye examination, visual fields, colour vision, dark adaptation and electroretinogram (ERG) were examined. RESULTS: Ten affected men aged 6 to 81 years were found in the family. The visual acuities varied from counting fingers (cf) 10 cm to 0.5 in the right eye (RE) and from cf 30 cm to 0.4 in the left eye (LE). The refraction was myopic in all affected members, varying from -1.5 to -24.0 D (RE) and from -2.0 to -20.25 D (LE). In visual functions, central scotomas and concentric constriction in the visual fields, red or red-green defects in colour vision, abnormal cone and rod dark adaptation and affected cone response in ERG were found. The 6 obligate carriers were aged 17 to 77 years. Their visual acuities varied from 0.05 (strabismic amblyopia) to 1.25(RE) and from 0.7 to 1.25 (LE), and refraction from +/-0 to +6.0 D (RE) and from -0.5 to +5.0 D (LE). Their visual fields and colour vision were normal. The non-affected men were aged 13 to 55 years, their visual acuity was normal in both eyes, and refraction varied from -5.0 to +1.5 D (RE) and from -5.5 to +1.75 (LE). The result of the eye examination was normal except in colour vision: two men were congenitally deuteranomalous. The women who were not obligate carriers were aged 10 to 77 years, their visual acuity was from 0.3 to 1.6 in both eyes, and refraction from -5.5 to +4.75 (RE) and from -5.25 to +4.0 (LE). Two women had one amblyopic eye. Otherwise the eye examination was normal. CONCLUSIONS: The clinical diagnosis of X-linked cone dystrophy 1 (COD1) is based on progressive loss of visual acuity, moderate or high myopia, red colour vision defect and affected cone response or cone and rod response in ERG. The future identification of the COD1 gene will confirm the diagnosis of the disease and help in genetic counseling of the family.

Adult↗

PubMed2004

Novel complex GUCY2D mutation in Japanese family with cone-rod dystrophy.

PURPOSE: All mutations in the retinal guanylate cyclase gene (GUCY2D) that causes autosomal dominant cone-rod dystrophy (CORD) are associated with an amino acid substitution in codon 838. A novel heterozygous complex missense mutation of I915T and G917R in the GUCY2D gene was found in a Japanese family with autosomal dominant CORD. The clinical features associated with this mutation were described. METHODS: Blood samples were collected from 27 patients with cone-rod or cone dystrophies and from 11 patients with macular dystrophy. Genomic DNA was extracted from peripheral leukocytes. All 18 coding exons of the GUCY2D gene were directly sequenced. The PCR product carrying a novel mutation was subcloned, and each allele was sequenced. A complete ophthalmologic examination was performed in members of the family with the novel mutation. RESULTS: A novel heterozygous complex missense mutation of T2817C and G2822C that would predict I915T and G917R amino acid substitutions, respectively, was found in an autosomal dominant CORD family. The two nucleotide changes were located on the same allele, and segregated with the disease. Two other known missense mutations of R838H and R838C were found in two other CORD families. The clinical phenotype associated with the novel mutation was similar to that with the Arg838 mutations. CONCLUSIONS: A heterozygous complex mutation of I915T and G917R in the GUCY2D gene caused autosomal dominant CORD, indicating that a heterozygous mutation that does not include a codon 838 substitution can lead to this ocular phenotype.

Adult↗

PubMed2026

Compound Heterozygous PCDH15 Variants Associated With Cone-Rod Dystrophy in a Chinese Pedigree.

BACKGROUND: This study aimed to characterize the clinical and genetic features of a Chinese family with cone-rod dystrophy in which compound heterozygous PCDH15 variants were identified. METHODS: A Chinese pedigree with autosomal recessive cone-rod dystrophy was investigated. A comprehensive ophthalmic assessment was performed in the proband, a 42-year-old woman, together with genetic evaluation of her family members. Candidate variants were identified using whole-exome sequencing and subsequently assessed by Sanger sequencing and family segregation analysis. RESULTS: Ophthalmoscopic examination revealed pigmentary changes and atrophic lesions affecting the posterior pole and peripapillary area bilaterally. Optical coherence tomography (OCT) demonstrated bilateral outer retinal layer atrophy with disruption of the ellipsoid zone at the posterior pole. Multifocal electroretinography (mfERG) revealed attenuated central responses, while full-field electroretinography (ffERG) documented a more pronounced reduction in cone-mediated (photopic) responses. Two novel compound heterozygous variants in PCDH15, namely c.4903_4906del (p.Glu1635Lysfs*4) and c.3470C>A (p.Ala1157Glu), were identified in this autosomal recessive cone-rod dystrophy pedigree. Family co-segregation analysis provided supportive evidence for their potential association with the disease phenotype. Cross-species analysis revealed high evolutionary conservation of the PCDH15 protein. Three-dimensional structural modeling predicted potential alterations in protein structure. CONCLUSION: To our knowledge, this is the first report describing an association between compound heterozygous PCDH15 variants and cone-rod dystrophy, thereby providing preliminary evidence that may broaden the mutational spectrum associated with this gene.

Adult↗

PubMed1975

Dominant cone-rod dystrophy.

Six generations of a family were studied extensively allowing the description of an autosomal dominant dystrophy of both rods and cones. The dystrophy is characterized by onset between ages 6 and 8 with gradual decrease in vision and progression to the point of no light perception. Abnormalities of color vision, visual field, refraction, fixation behavior, fundus appearance, fluorescein angiography, electroretinography, electrooculography and dark adaptation are presented. The importance of this family in the classification of inherited retinal dystrophies is stressed and the need for an expanded classification is discussed. The role of genetic counseling is stressed in such severe diseases.

Adult↗

PubMed1998

Abnormal cone synapses in human cone-rod dystrophy.

OBJECTIVE: Little is known of the cytopathology of photoreceptors in human inherited retinal dystrophies that initially affect the central retina, including the macula. The current study sought to determine the cytologic features of dysfunctional cone and rod photoreceptors, as well as the pattern of degeneration of the cells in representative cases of central retinal dystrophy. STUDY DESIGN: Comparative human tissue study. MATERIALS: Four human donor eyes with the following forms of central retinal dystrophy: cone-rod dystrophy (CRD), central areolar choroidal dystrophy, Bardet-Biedl syndrome, and cone dystrophy-cerebellar ataxia. The cytologic features of retinal photoreceptors in these eyes were compared with those in an eye with retinitis pigmentosa and six normal human eyes. METHODS AND OUTCOME MEASURES: Immunocytochemistry and electron microscopy were used to evaluate the retinal histopathology in the donor eyes. RESULTS: Cone numbers were decreased in the case of CRD, particularly in the central and far peripheral retina, and both cone and rod outer segments were slightly shortened. Occasional degenerate cones had dense cytoplasm and pyknotic nuclei dislocated sclerad to the external-limiting membrane. The most prominent alteration in this retina was marked enlargement and distortion of the cone photoreceptor pedicles, which contained reduced numbers of synaptic vesicles. The retina with central areolar choroidal dystrophy contained a few cones with similarly abnormal synapses. However, comparable cone synapse abnormalities were not observed in the cases of Bardet-Biedl syndrome, cone dystrophy-cerebellar ataxia, retinitis pigmentosa, or in the normal retinas. CONCLUSIONS: The functional consequences of the cone synapse abnormalities in CRD are not known but may correlate with the electroretinographic abnormalities documented in some cases of CRD. To our knowledge, comparable synapse changes have not been noted in either rods or cones in other forms of retinal dystrophy, including retinitis pigmentosa, suggesting that different cytopathologic mechanisms may be involved.

Adult↗

PubMed1995

Autosomal dominant cone-rod dystrophy with negative electroretinogram.

AIMS: The negative electroretinogram (ERG) is observed in many hereditary retinal disorders. However, no reports have described a negative ERG in a family with autosomal dominant cone-rod dystrophy. A Japanese family with autosomal dominant cone-rod dystrophy with negative ERG is described. METHOD: Members of a Japanese family with autosomal dominant cone-rod dystrophy were examined and evaluated with Goldmann and Humphrey perimetry, bright flash ERG with an intense white stimulus, rod, cone, and flicker ERGs, and fluorescein angiography. Molecular analysis of the rhodopsin and peripherin/RDS genes in the patients was also performed. RESULTS: A 45-year-old Japanese man (proband) presented with decreased visual acuity. His fundi revealed bull's eye maculopathy and his single flash bright ERG showed a negative configuration. Negative ERG responses also were found in his father, who had macular degeneration, and one of the proband's three children who showed no fundus changes. No irregularities were found in their rhodopsin or peripherin/RDS genes. CONCLUSION: The condition of this family is believed to represent a previously undescribed autosomal dominant cone-rod dystrophy.

Adolescent↗

PubMed2003

Alterations of L- and M-cone driven ERGs in cone and cone-rod dystrophies.

To study the L- and M-cone pathways and their interactions in patients with cone and cone-rod dystrophies, ERG responses were measured to stimuli which modulated exclusively the L- or the M-cones, or the two simultaneously. The L- and M-cone driven ERG amplitudes were considerably reduced in the patients. The mean phases of the L-cone driven ERGs in the patients lagged those of normals significantly, whereas the mean M-cone driven ERGs were significantly phase advanced resulting in a substantial phase difference between the two ERG responses. These phase changes in the L- and M-cone driven responses in the patients cannot be detected with standard ERG techniques.

Electroretinography↗

PubMed2005

A novel locus for autosomal dominant cone and cone-rod dystrophies maps to the 6p gene cluster of retinal dystrophies.

PURPOSE: To characterize clinically and genetically a four-generation Italian family with autosomal dominant retinal dystrophy. METHODS: Thirty-seven family members underwent a detailed ophthalmologic investigation, comprising visual acuity determination, fundoscopy, electroretinogram, and electrooculogram. A genome-wide scan was performed, and three candidate genes mapping to the linked region were screened for mutations by direct sequencing. RESULTS: Nineteen individuals were affected by cone-rod dystrophy and four by cone dystrophy, whereas, in another subject, the diagnosis was compatible with central areolar choroidal dystrophy. The genome-wide search allowed mapping the disease locus to chromosome 6, region p12.2-p21.1, with a maximum lod score of 6.71. Analysis of key recombinants in affected individuals placed the locus to a 12-Mb region flanked by newly generated markers 6-41025 and 6-52969. Assuming complete penetrance, recombinations in two healthy individuals defined a smaller critical region of 3.7 Mb between markers 6-42153 and D6S459. Three genes mapping within the linked interval (RDS, GUCA1A, and GUCA1B) were considered excellent candidates because of their involvement in distinct forms of retinal dystrophies. However, mutation analyses of these genes failed to identify pathogenetic mutations. CONCLUSIONS: The significant lod scores obtained and the absence of mutations in RDS, GUCA1A, and GUCA1B support the existence of a novel, yet unidentified gene responsible for retinal dystrophy within the chromosome 6 cluster.

Adult↗

PubMed2003

ABCA4 gene sequence variations in patients with autosomal recessive cone-rod dystrophy.

OBJECTIVE: To identify sequence variations in the ABCA4 gene in a cohort of patients with autosomal recessive cone-rod dystrophy. METHODS: The coding sequences of the ABCA4 gene were analyzed in 30 unrelated probands. In those patients with plausible disease-causing variations, correlations were made between genotype and fundus phenotype as well as with electrophysiological and visual field findings. RESULTS: Sixteen (53%) of 30 probands were found to harbor plausible disease-causing variations in the ABCA4 gene. Two distinctly different fundus phenotypes were observed in our cohort of patients. Twelve patients showed diffuse pigmentary degenerative changes, whereas 4 showed either no pigmentary changes or only a mild degree of peripheral pigment degeneration. An associa-tion between certain sequence variations and each of these 2 different phenotypes was observed. CONCLUSIONS: Our findings confirm that a substantial percentage of patients with autosomal recessive cone-rod dystrophy are likely to harbor a mutation in the ABCA4 gene as the cause of their disease. The fundus phenotype observed in such patients is quite variable, and certain fundus phenotypes may be more associated with certain genotypes. Clinical Relevance Identification of the molecular genetic basis for various inherited human retinal dystrophies, such as cone-rod dystrophy, facilitates a potentially better understanding of the mechanisms by which photoreceptor cells degenerate. This in turn provides guidance as to how to better proceed in identifying the most optimal future therapeutic strategies.

ATP-Binding Cassette Transporters↗

PubMed1994

The importance of fluorescein angiography in diagnosing pattern dystrophies of the retinal pigment epithelium.

We describe three different types of pattern dystrophies in the retinal pigment epithelium: annular dystrophy, butterfly-shaped dystrophy with features of cone dystrophy, and butterfly dystrophy. In all the cases, fluorescein angiography was a good method to evaluate the morphology and range of macular changes. The butterfly-shaped lesions were not always easily visible with the ophthalmoscope, therefore, the fluorescein angiography was diagnostic. We also examined 17 relatives of these patients to discover the mode of inheritance in these diseases. The annular dystrophy seemed to be recessively inherited or a possible sporadic case, as was the unusual pattern dystrophy with features of cone dystrophy. The dominant heredity was found in the typical cases of butterfly-pattern dystrophy.

Adolescent↗

PubMed2002

X-linked cone-rod dystrophy (locus COD1): identification of mutations in RPGR exon ORF15.

X-linked cone-rod dystrophy (COD1) is a retinal disease that primarily affects the cone photoreceptors; the disease was originally mapped to a limited region of Xp11.4. We evaluated the three families from our original study with new markers and clinically reassessed all key recombinants; we determined that the critical intervals in families 2 and 3 overlapped the RP3 locus and that a status change (from affected to probably unaffected) of a key recombinant individual in family 1 also reassigned the disease locus to include RP3 as well. Mutation analysis of the entire RPGR coding region identified two different 2-nucleotide (nt) deletions in ORF15, in family 2 (delAG) and in families 1 and 3 (delGG), both of which result in a frameshift leading to altered amino acid structure and early termination. In addition, an independent individual with X-linked cone-rod dystrophy demonstrated a 1-nt insertion (insA) in ORF15. The presence of three distinct mutations associated with the same disease phenotype provides strong evidence that mutations in RPGR exon ORF15 are responsible for COD1. Genetic heterogeneity was observed in three other families, including the identification of an in-frame 12-nt deletion polymorphism in ORF15 that did not segregate with the disease in one of these families.

Amino Acid Sequence↗

PubMed1991

Deletion mapping of a retinal cone-rod dystrophy: assignment to 18q211.

Deletion of 18q211 was observed in a mentally retarded young man with electrophysiologically demonstrated cone-rod dystrophy, present since childhood. He had hypogonadism and a central postsynaptic hearing impairment. This is the first case of a chromosome deletion in a patient with a cone-rod dystrophy. Three patients with more distal deletions on chromosome 18 did not present retinal dystrophies. We suggest that one of the loci for cone-rod dystrophy may be located on chromosome 18 at q211-213. Reports of similar findings will be necessary for confirmation of this assumption.

Abnormalities, Multiple↗

PubMedDate not supplied

Progressive cone and cone-rod dystrophies: phenotypes and underlying molecular genetic basis.

The cone and cone-rod dystrophies form part of a heterogeneous group of retinal disorders that are an important cause of visual impairment in children and adults. There have been considerable advances made in recent years in our understanding of the pathogenesis of these retinal dystrophies, with many of the chromosomal loci and causative genes having now been identified. Mutations in 12 genes, including GUCA1A, peripherin/RDS, ABCA4 and RPGR, have been described to date; and in many cases detailed functional assessment of the effects of the encoded mutant proteins has been undertaken. This improved knowledge of disease mechanisms has raised the possibility of future treatments for these disorders, for which there are no specific therapies available at the present time.

DNA↗

PubMed2001

Isolated late-onset cone-rod dystrophy revealing a familial neurogenic muscle weakness, ataxia, and retinitis pigmentosa syndrome with the T8993G mitochondrial mutation.

PURPOSE: To report a late-onset cone-rod dystrophy that revealed a familial neurogenic muscle weakness, ataxia, and retinitis pigmentosa syndrome as a consequence of the T8993G mitochondrial mutation. METHODS: Observational case series. A 42-year-old female disclosed a late-onset retinal dystrophy. The family history revealed that her three sons, one of them deceased at the age of 4, had mental and neurologic impairment of variable severity. The retinal dystrophy of the mother was classified as a cone-rod dystrophy. Retinal dystrophy was subsequently diagnosed in the two surviving sons. Screening for mutation in the mitochondrial DNA (mtDNA) was performed because of the combination of neurologic involvement and retinal dystrophy in this family. RESULTS: Molecular analysis of the mtDNA revealed the ATPase-6 gene T8993G mutation in the mother and the two sons. CONCLUSION: This family illustrates the remarkably variable expression of retinal and systemic manifestations related to the T8993G mutation ranging from an isolated late-onset cone-rod dystrophy to a severe neurodegenerative process with a dramatic outcome. Genetic counseling for retinal dystrophies requires careful evaluation of the familial medical history.

Adenosine Triphosphatases↗

PubMed2004

Dominant cone and cone-rod dystrophies: functional analysis of mutations in retGC1 and GCAP1.

The regulation of cGMP levels is central to the normal process of phototransduction in both cone and rod photoreceptor cells. Two of the proteins involved in this process are the enzyme, retinal guanylate cyclase (retGC), and its activating protein (GCAP) through which activity is regulated via changes in cellular Ca2+ levels. Dominant cone-rod dystrophies arising from changes in retGC1 are essentially restricted to mutations in codon 838 and result in the replacement of a conserved arginine residue with either cysteine, histidine or serine. In all three cases, the effect of the substitution on the in vitro cyclase activity is a loss of Ca2+ sensitivity arising from an increased stability of the coiled-coil domain of the protein dimer and retention of cyclase activity. In contrast, mutations in the Ca2+-coordinating EF hands of GCAP1 result in dominant cone dystrophy; the consequences of these mutations is a reduced ability of the mutant protein to regulate retGC activity in response to changes in Ca2+ levels. Functionally therefore, the retGC2 and GCAP2 mutations are similar in reducing the feedback inhibition of Ca2+ on cyclase activity and thereby on cGMP levels in the photoreceptors.

Calcium↗

PubMed1981

Dominant progressive cone-rod dystrophy.

The report describes a Finnish family in which retinal lesions associated with a considerable visual loss have been found in 19 probands in 5 consecutive generations. The progressive cone-rod dystrophy diagnosed in the probands shows an autosomal dominant mode of inheritance. The onset of the disease was noticed in most of the probands early during the first decade of life. In the young diseased probands the fundal lesions showed the pattern found in pure cone dystrophies. Elder probands, however, had lesions and dysfunctions indicating an obvious rod involvement in addition to the cone dystrophic pattern. The fundal lesions included very extensive pigmentation in most of the elder probands with the disease. In addition to the retinal lesions, considerable astigmatism and lens opacities at the level of the posterior capsule were found in a great proportion of the probands.

Adolescent↗

PubMed2000

Autosomal dominant cone-rod dystrophy due to a missense mutation (R838C) in the guanylate cyclase 2D gene (GUCY2D) with preserved rod function in one branch of the family.

We present the clinical and molecular genetic features of a large multi-generation Norwegian family with dominant cone-rod dystrophy. Ophthalmological evaluation including electroretinography showed cone dysfunction in younger patients, with rod dysfunction becoming apparent at more advanced stages of the disease. In one branch of the family, cone degeneration remained the only manifestation despite advancing age. Linkage analysis mapped the disease gene in this family to 17p12-p13, a chromosome region previously linked to cone-rod dystrophy in a Swedish family (CORD5). A maximum LOD score of 3.25 (straight theta = 0.00) for marker D17S1844 was obtained. Mutation analysis of the guanylate cyclase 2D gene (GUCY2D, MIM 600179, previously called RETGC1), located at 17p12-p13, showed a missense mutation (R838C) in exon 13, that co-segregated with the eye disease in the family. Our suspicion of the possibility of an interrelationship between the Swedish CORD5 family and the present family, both originating from Northern Scandinavia, initiated the linkage analysis in the Norwegian family. The R838C missense mutation was not, however, detected in the Swedish patients, strongly suggesting no relationship between these two families. The long-term ophthalmological evaluation in this large four-generation family, combined with the identification of the disease-causing mutation, provide critical information for refining the classification, prognosis, and genetic counselling of patients with cone-rod dystrophies.

Adult↗