Cone and cone-rod dystrophies

A GUCY2D variant associated cone-rod dystrophy with electronegative ERG: A case report and review

Purpose

Cone-rod dystrophies (CORD) are inherited retinal dystrophies characterized by primary cone degeneration with secondary rod involvement. We report two patients from the same family with a dominant variant in the guanylate cyclase 2D (GUCY2D) gene with different phenotypes in the electroretinogram (ERG).

Observations

A 21-year-old lady (Patient 1) was referred due to experiencing blurry vision and color vision impairment. Visual field testing revealed a central scotoma. Spectral-domain optical coherence tomography (SD-OCT) and fundus autofluorescence (FAF) documented macula dysfunction. Reduced amplitude was observed in the photopic responses of ERG. Her 54-year-old father (Patient 2) had similar issues with blurry vision. A dilated fundus examination displayed bilateral macular atrophy. Loss of the ellipsoid zone line and collapse of the outer nuclear segment were noted on the SD-OCT. Photopic ERG responses were extinguished, and an electronegative ERG was observed in the dark-adapted 3.0 ERG. The gene report revealed a c.2512C > T (p.Arg838Cys) variant in GUCY2D for both patients. They were respectively diagnosed as cone dystrophy (COD) and cone-rod dystrophy (CORD).

Conclusions

We report two different clinical phenotypes in GUCY2D-associated COD despite sharing the same variant. A dysfunction in the synaptic junction between the photoreceptor and the secondary neuron was proposed to explain the electronegative ERG. This explanation might extend to other gene-related cases of CORD with electronegative ERG.

Whole genome sequencing for inherited retinal diseases in the Korean National Project of Bio Big Data

PURPOSE

This study aimed to analyze the genetic results of inherited retinal diseases (IRDs) and evaluate the diagnostic usefulness of whole genome sequencing (WGS) in the Korean National Project of Bio Big Data.

METHODS

As part of the Korean National Project of Bio Big Data, WGS was performed on 32 individuals with IRDs with no identified pathogenic variants through whole or targeted exome sequencing.

RESULTS

Individuals with retinitis pigmentosa (n = 23), cone dystrophy (n = 2), cone-rod dystrophy (n = 2), familial exudative vitreoretinopathy (n = 2), pigmented paravenous chorioretinal atrophy (n = 1), North Carolina macular dystrophy (n = 1), and bull's-eye macular dystrophy (n = 1) were included. WGS revealed genetic mutations in the IQCB1, PRPF31, USH2A, and GUCY2D genes in five cases (15.6%). Two large structural variations and an intronic variant were newly detected in three cases. Two individuals had biallelic missense mutations that were not identified in previous exome sequencing.

CONCLUSION

With WGS, the causative variants in 15.6% of unsolved IRDs from the Korean National Project of Bio Big Data were identified. Further research with a larger cohort might unveil the diagnostic usefulness of WGS in IRDs and other diseases.

Metabolic Syndromes as Important Comorbidities in Patients of Inherited Retinal Degenerations: Experiences from the Nationwide Health Database and a Large Hospital-Based Cohort

This study aimed to evaluate the medical and socioeconomic impacts of IRDs using the nationwide health database and a large hospital-based cohort. This retrospective cross-sectional cohort study used data from the nationwide National Health Insurance Research Database (NHIRD). All patients with IRD from January 2012 to December 2016 were selected from the NHIRD and matched with the general population at a ratio of 1:4. All variables, including comorbidities, medications, service utilization, and medical costs, within 1 year from the date of the IRD diagnosis, were analyzed. Disability data were retrieved from the Taiwan Inherited retinal degeneration Project (TIP), a medical center-based database. A total of 4447 and 17,788 subjects from the nationwide database were included in the IRD and control groups, respectively. The Charlson comorbidity index score was higher in the IRD group (0.74:0.52, p < 0.001). Yearly visits to the ophthalmology clinic were more frequent in the IRD group (6.80:1.06, p < 0.001), particularly to tertiary medical centers (p < 0.001). The IRD group showed greater odds ratios (OR) for metabolic syndrome-related comorbidities, including hypertension (OR = 1.18, 95% confidence interval (CI) 1.10 to 1.26) and diabetes (OR = 1.32, 95% CI 1.21 to 1.45), and double the average yearly medical cost (2104.3 vs. 1084.6 USD, p < 0.001) and ten times the yearly ophthalmology cost (369.1 vs. 36.1 USD, p < 0.001). The average disability level was 54.17% for all subjects. This study revealed the large medical and socioeconomic impacts of IRD on not only patients with IRD, but also their family members and the whole society.

Genetic characteristics and epidemiology of inherited retinal degeneration in Taiwan

Inherited retinal degenerations (IRDs) are a group of phenotypically and genotypically heterogeneous disorders with substantial socioeconomic impact. In this cohort study, we tried to address the genetic characteristics and epidemiology of IRDs in Taiwan. Totally, 312 families with IRDs were identified and recruited and genetic testing was performed via probe capture-based NGS targeting 212 IRD-related genes. Statistical analysis was based on the proband of each affected family. Disease-causing genotypes were identified in 178 families (57.1%). ABCA4 variants were the most common cause of disease in this cohort (27 families, 15.2%), whereas CYP4V2 variants were the most common cause for the single phenotype—Bietti’s crystalline dystrophy (12 families, 3.8%). Some variants such as ABCA4:c.1804C>T, CYP4V2:c.802-8_810delinsGC, and EYS:c6416G>A were population-specific disease-causing hotspots. Probands affected by ABCA4, RPGR, RP1L1, and CEP290 sought medical help earlier while patients affected by EYS and CYP4V2 visited our clinic at an older age. To evaluate the representativeness of our cohort in the genetic epidemiology of IRDs in Taiwan, our demographic data were compared with that of the total IRD population in Taiwan, obtained from the National Health Insurance Research Database. This is currently the largest-scale, comprehensive study investigating the genetic characteristics and epidemiology of IRD in Taiwan. These data could help patients and caregivers to adopt precision genomic medicine and novel gene therapies in near future.

Reviewing the Role of Ultra-Widefield Imaging in Inherited Retinal Dystrophies

Inherited retinal dystrophies (IRD) are a heterogeneous group of rare chronic disorders caused by genetically determined degeneration of photoreceptors and retinal pigment epithelium cells. Ultra-widefield (UWF) imaging is a useful diagnostic tool for evaluating retinal integrity in IRD, including Stargardt disease, retinitis pigmentosa, cone dystrophies, and Best vitelliform dystrophy. Color or pseudocolor and fundus autofluorescence images obtained with UWF provide previously unavailable information on the retinal periphery, which correlates well with visual field measurement or electroretinogram. Despite unavoidable artifacts of the UWF device, the feasibility of investigations in infants and in patients with poor fixation makes UWF imaging a precious resource in the diagnostic armamentarium for IRD.

A novel pathogenic missense variant in CNNM4 underlying Jalili syndrome: Insights from molecular dynamics simulations

Background

Jalili syndrome (JS) is a rare cone‐rod dystrophy (CRD) associated with amelogenesis imperfecta (AI). The first clinical presentation of JS patients was published in 1988 by Jalili and Smith. Pathogenic mutations in the Cyclin and CBS Domain Divalent Metal Cation Transport Mediator 4 (CNNM4) magnesium transporter protein have been reported as the leading cause of this anomaly.

Methods

In the present study, a clinical and genetic investigation was performed in a consanguineous family of Pakistani origin, showing characteristic features of JS. Sanger sequencing was successfully used to identify the causative variant in CNNM4. Molecular dynamics (MD) simulations were performed to study the effect of amino acid change over CNNM4 protein.

Results

Sequence analysis of CNNM4 revealed a novel missense variant (c.1220G>T, p.Arg407Leu) in exon‐1 encoding cystathionine‐β‐synthase (CBS) domain. To comprehend the mutational consequences in the structure, the mutant p.Arg407Leu was modeled together with a previously reported variant (c.1484C>T, p.Thr495Ile) in the same domain. Additionally, docking analysis deciphered the binding mode of the adenosine triphosphate (ATP) cofactor. Furthermore, 60ns MD simulations were carried out on wild type (p.Arg407/p.Thr495) and mutants (p.Arg407Leu/p.Thr495Ile) to understand the structural and energetic changes in protein structure and its dynamic behavior. An evident conformational shift of ATP in the binding site was observed in simulated mutants disrupting the native ATP‐binding mode.

Conclusion

The novel identified variant in CNNM4 is the first report from the Pakistani population. Overall, the study is valuable and may give a novel insight into metal transport in visual function and biomineralization.

Somatic Gene Editing of GUCY2D by AAV-CRISPR/Cas9 Alters Retinal Structure and Function in Mouse and Macaque

Mutations in GUCY2D, the gene encoding retinal guanylate cyclase-1 (retGC1), are the leading cause of autosomal dominant cone-rod dystrophy (CORD6). Significant progress toward clinical application of gene replacement therapy for Leber congenital amaurosis (LCA) due to recessive mutations in GUCY2D (LCA1) has been made, but a different approach is needed to treat CORD6 where gain of function mutations cause dysfunction and dystrophy. The CRISPR/Cas9 gene editing system efficiently disrupts genes at desired loci, enabling complete gene knockout or homology directed repair. Here, adeno-associated virus (AAV)-delivered CRISPR/Cas9 was used specifically to edit/disrupt this gene's early coding sequence in mouse and macaque photoreceptors in vivo, thereby knocking out retGC1 expression and demonstrably altering retinal function and structure. Neither preexisting nor induced Cas9-specific T-cell responses resulted in ocular inflammation in macaques, nor did it limit GUCY2D editing. The results show, for the first time, the ability to perform somatic gene editing in primates using AAV-CRISPR/Cas9 and demonstrate the viability this approach for treating inherited retinal diseases in general and CORD6 in particular.

Novel variants identified with next-generation sequencing in Polish patients with cone-rod dystrophy

Purpose

The aim of this study was to identify the molecular genetic basis of cone-rod dystrophy in 18 unrelated families of Polish origin. Cone-rod dystrophy is one of the inherited retinal dystrophies, which constitute a highly heterogeneous group of disorders characterized by progressive dysfunction of photoreceptors and retinal pigment epithelium (RPE) cells.

Methods

The study group was composed of four groups of patients representing different Mendelian inheritance of the disease: autosomal dominant (AD), autosomal recessive (AR), X-linked recessive (XL), and autosomal recessive or X-linked recessive (AR/XL). The combined molecular strategy included Sanger sequencing of the RPGR-ORF15 gene (three families with XL and three families with the AR/XL mode of inheritance), mutation-specific microarray analysis of the ABCA4 gene (five families with the AR mode of inheritance and two families with the AR/XL mode of inheritance), targeted next-generation sequencing (NGS) of inherited retinal disease-associated (IRD) genes (seven families with the AD mode of inheritance and five families with the AR mode of inheritance), and whole exome sequencing, performed in select families who had been mutation-negative in the analysis with the targeted NGS panel (one family with the AD mode of inheritance, one family with the AR mode of inheritance, and two families with the AR/XL mode of inheritance).

Results

Based on this combined strategy, we managed to identify potentially causative variants in seven out of 18 families with CRD. Five of these variants are novel: c.3142_3143dupAA, p.(Glu1049Argfs*41) in the RPGR-ORF15 gene, two variants: c.1612delT, p.(Trp538Glyfs*15) and c.2389dupG, p.(Ile798Hisfs*20) in the PROM1 gene in one family, c.592A>C, p.(Ser198Arg) in the PRPH2 gene and the variant c.1691A>G, p.(Asp564Gly) in the ATF6 gene that we have already reported to be pathogenic. NGS on the IRD panel allowed the molecular basis of CRD to be identified in four out of 14 families with a total detection rate of 38%. WES allowed identification of the molecular genetic basis of CRD in one family.

Conclusions

This is the first report on the spectrum of disease genes and pathogenic variants causing CRD in the Polish population. The study presents five novel variants identified in four genes and therefore, broadens the spectrum of probable pathogenic variants associated with CRD.

Digital LED Pixels: Instructions for use and a characterization of their properties

This article details how to control light emitting diodes (LEDs) using an ordinary desktop computer. By combining digitally addressable LEDs with an off-the-shelf microcontroller (Arduino), multiple LEDs can be controlled independently and with a high degree of temporal, chromatic, and luminance precision. The proposed solution is safe (can be powered by a 5-V battery), tested (has been used in published research), inexpensive (∼ $60 + $2 per LED), highly interoperable (can be controlled by any type of computer/operating system via a USB or Bluetooth connection), requires no prior knowledge of electrical engineering (components simply require plugging together), and uses widely available components for which established help forums already exist. Matlab code is provided, including a ‘minimal working example’ of use suitable for use by beginners. Properties of the recommended LEDs are also characterized, including their response time, luminance profile, and color gamut. Based on these, it is shown that the LEDs are highly stable in terms of both luminance and chromaticity, and do not suffer from issues of warm-up, chromatic shift, and slow response times associated with traditional CRT and LCD monitor technology.

Stem Cell Ophthalmology Treatment Study (SCOTS): bone marrow-derived stem cells in the treatment of Leber's hereditary optic neuropathy

The Stem Cell Ophthalmology Treatment Study (SCOTS) is currently the largest-scale stem cell ophthalmology trial registered at ClinicalTrials.gov (identifier: NCT01920867). SCOTS utilizes autologous bone marrow-derived stem cells (BMSCs) to treat optic nerve and retinal diseases. Treatment approaches include a combination of retrobulbar, subtenon, intravitreal, intra-optic nerve, subretinal, and intravenous injection of autologous BMSCs according to the nature of the disease, the degree of visual loss, and any risk factors related to the treatments. Patients with Leber's hereditary optic neuropathy had visual acuity gains on the Early Treatment Diabetic Retinopathy Study (ETDRS) of up to 35 letters and Snellen acuity improvements from hand motion to 20/200 and from counting fingers to 20/100. Visual field improvements were noted. Macular and optic nerve head nerve fiber layer typically thickened. No serious complications were seen. The increases in visual acuity obtained in our study were encouraging and suggest that the use of autologous BMSCs as provided in SCOTS for ophthalmologic mitochondrial diseases including Leber's hereditary optic neuropathy may be a viable treatment option.

Chaotic analysis of the electroretinographic signal for diagnosis

Electroretinogram (ERG) is a time-varying potential which arises from different layers of retina. To be specific, all the physiological signals may contain some useful information which is not visible to our naked eye. However this subtle information is difficult to monitor directly. Therefore the ERG signal features which are extracted and analyzed using computers are highly useful for diagnosis. This work discusses the chaotic aspect of the ERG signal for the controls, congenital stationary night blindness (CSNB), and cone-rod dystrophy (CRD) classes. In this work, nonlinear parameters like Hurst exponent (HE), the largest Lyapunov exponent (LLE), Higuchi's fractal dimension (HFD), and approximate entropy (ApEn) are analyzed for the three different classes. It is found that the measures like HE dimension and ApEn are higher for controls as compared to the other two classes. But LLE shows no distinguishable variation for the three cases. We have also analyzed the recurrence plots and phase-space plots which shows a drastic variation among the three groups. The results obtained show that the ERG signal is highly complex for the control groups and less complex for the abnormal classes with P value less than 0.05.

Exome sequencing of index patients with retinal dystrophies as a tool for molecular diagnosis

BACKGROUND

Retinal dystrophies (RD) are a group of hereditary diseases that lead to debilitating visual impairment and are usually transmitted as a Mendelian trait. Pathogenic mutations can occur in any of the 100 or more disease genes identified so far, making molecular diagnosis a rather laborious process. In this work we explored the use of whole exome sequencing (WES) as a tool for identification of RD mutations, with the aim of assessing its applicability in a diagnostic context.

METHODOLOGY/PRINCIPAL FINDINGS

We ascertained 12 Spanish families with seemingly recessive RD. All of the index patients underwent mutational pre-screening by chip-based sequence hybridization and resulted to be negative for known RD mutations. With the exception of one pedigree, to simulate a standard diagnostic scenario we processed by WES only the DNA from the index patient of each family, followed by in silico data analysis. We successfully identified causative mutations in patients from 10 different families, which were later verified by Sanger sequencing and co-segregation analyses. Specifically, we detected pathogenic DNA variants (∼50% novel mutations) in the genes RP1, USH2A, CNGB3, NMNAT1, CHM, and ABCA4, responsible for retinitis pigmentosa, Usher syndrome, achromatopsia, Leber congenital amaurosis, choroideremia, or recessive Stargardt/cone-rod dystrophy cases.

CONCLUSIONS/SIGNIFICANCE

Despite the absence of genetic information from other family members that could help excluding nonpathogenic DNA variants, we could detect causative mutations in a variety of genes known to represent a wide spectrum of clinical phenotypes in 83% of the patients analyzed. Considering the constant drop in costs for human exome sequencing and the relative simplicity of the analyses made, this technique could represent a valuable tool for molecular diagnostics or genetic research, even in cases for which no genotypes from family members are available.

Ophthalmologic stem cell transplantation therapies

Vision loss is a major social issue, with more than 20 million people over the age of 18 years affected in the USA alone. Loss of vision is feared more than premature death or cardiovascular disease, according to a recent Society for Consumer Research group survey. The annual direct cost of medical care for the most prevalent eye disease, age-related macular degeneration, was estimated at US$255 billion in 2010 with an additional economic impact of US$88 billion due to lost productivity and the burden of family and community care for visual disability. With the blossoming of human stem cell research, regenerative treatments are now being developed that can help reduce this burden. Positive results from animal studies demonstrate that stem cell-based transplants can preserve and potentially improve vision. This has led to new clinical trials for several eye diseases that are yielding encouraging results. In the next few years, additional trials and longer-term results are anticipated to further develop ocular regenerative therapies, with the potential to revolutionize our approach to ophthalmic disease and damage.

A novel locus for autosomal dominant cone-rod dystrophy maps to chromosome 10q

Here we report recruitment of a three-generation Romani (Gypsy) family with autosomal dominant cone-rod dystrophy (adCORD). Involvement of known adCORD genes was excluded by microsatellite (STR) genotyping and linkage analysis. Subsequently, two independent total-genome scans using STR markers and single-nucleotide polymorphisms (SNPs) were performed. Haplotype analysis revealed a single 6.7-Mb novel locus between markers D10S1757 and D10S1782 linked to the disease phenotype on chromosome 10q26. Linkage analysis gave a maximum LOD score of 3.31 for five fully informative STR markers within the linked interval corresponding to the expected maximum in the family. Multipoint linkage analysis of SNP genotypes yielded a maximum parametric linkage score of 2.71 with markers located in the same chromosomal interval. There is no previously mapped CORD locus in this interval, and therefore the data reported here is novel and likely to identify a new gene that may eventually contribute to new knowledge on the pathogenesis of this condition. Sequencing of several candidate genes within the mapped interval led to negative findings in terms of the underlying molecular pathogenesis of the disease in the family. Analysis by comparative genomic hybridization excluded large chromosomal aberrations as causative of adCORD in the pedigree.

Mutation analysis at codon 838 of the Guanylate Cyclase 2D gene in Spanish families with autosomal dominant cone, cone-rod, and macular dystrophies

PURPOSE

Heterozygous mutations around codon 838 of the guanylate cyclase 2D (GUCY2D) gene have recently been associated with more than a third of autosomal dominant macular dystrophy patients. The aim of our study was to evaluate the prevalence of these mutations in Spanish families with autosomal dominant cone, cone-rod, and macular dystrophies.

METHODS

Mutation analysis was performed by PCR amplification of exon 13 of GUCY2D and subsequent restriction analysis. To confirm the results, automatic sequencing analysis was also performed.

RESULTS

Among the 22 unrelated Spanish families included in the study, we found two associated disease mutations at codon 838 of the GUCY2D gene, one of which had not been previously described (p.R838P). This novel mutation exhibited phenotypic variability.

CONCLUSIONS

The prevalence of mutations around codon 838 of GUCY2D in our group of families (9.09%) is lower than that previously reported in other populations. However, the discovery of a novel mutation at codon 838 further suggests that this locus is a mutation hotspot within the GUCY2D gene, and confirms the importance of analyzing this codon to characterize molecularly these autosomal dominant retinal disorders.

A novel recessive GUCY2D mutation causing cone-rod dystrophy and not Leber's congenital amaurosis

Cone-rod dystrophies are inherited retinal dystrophies that are characterized by progressive degeneration of cones and rods, causing an early decrease in central visual acuity and colour vision defects, followed by loss of peripheral vision in adolescence or early adult life. Both genetic and clinical heterogeneity are well known. In a family with autosomal recessive cone-rod dystrophy, genetic analyses comprising genome scan with microsatellite markers, fine mapping and candidate gene approach resulted in the identification of a homozygous missense GUCY2D mutation. This is the first GUCY2D mutation associated with autosomal recessive cone-rod dystrophy rather than Leber's congenital amaurosis (LCA), a severe disease leading to childhood blindness. This study hence establishes GUCY2D, which is a common cause for both recessive LCA and dominant cone-rod dystrophy, as a good candidate for autosomal recessive cone-rod dystrophy.

Cone-rod dystrophy and a frameshift mutation in the PROM1 gene

PURPOSE

To identify the genetic cause underlying autosomal recessive cone-rod dystrophy (CORD) and high myopia.

METHODS

Nine members of a consanguineous Arab family were clinically examined and were given fluorescein angiography (FA), biometry, and full field electroretinogram (ERG) testing. Blood samples were collected for DNA extraction. A homozygousity genome-wide scan was performed using >382 polymorphic microsatellite markers on genomic DNA from three affected family members. Regions of homozygosity were further analyzed in all members of the family. Mutation analysis of the PROM1 gene was performed by direct sequencing of PCR-amplified exons.

RESULTS

The phenotype is characterized by severe visual impairment evident in the first decade of life. Affected family members have bull;s-eye macular appearance, peripheral retinal pigment clumps, and cone-rod type ERG changes. Additionally, they have high myopia with axial lengths exceeding 25.3 mm. A genome-wide scan detected a region of 2.1 Mb on chromosome 4p that fully segregates with the disease within the family. This region encompasses the PROML1 gene, mutations of which have been implicated in retinal dystrophies. PROML1 mutation analysis identified a novel single nucleotide insertion at position 1629 of the cDNA resulting in truncation of approximately one-third of the protein.

CONCLUSIONS

The mutation described in this report further expands the clinical spectrum of PROM1 mutations.

The retinal ciliopathies

While the functions of many of the proteins located in or associated with the photoreceptor cilia are poorly understood, disruption of the function of these proteins may result in a wide variety of phenotypes ranging from isolated retinal degeneration to more pleiotropic phenotypes. Systemic findings include neurosensory hearing loss, developmental delay, situs-inversus, infertility, disorders of limb and digit development, obesity, kidney disease, liver disease, and respiratory disease. The concept of "retinal ciliopathies" brings to attention the importance of further molecular analysis of this organelle as well as provides a potential common target for therapies for these disorders. The retinal ciliopathies include retinitis pigmentosa, macular degeneration, cone-dystrophy, cone-rod dystrophy, Leber congenital amaurosis, as well as retinal degenerations associated with Usher syndrome, primary ciliary dyskinesia, Senior-Loken syndrome, Joubert syndrome, Bardet-Biedl syndrome, Laurence-Moon syndrome, McKusick-Kaufman syndrome, and Biemond syndrome. Mutations for these disorders have been found in retinitis pigmentosa-1 (RP1), retinitis pigmentosa GTPase regulator (RPGR), retinitis pigmentosa GTPase regulator interacting protein (RPGR-IP), as well as the Usher, Bardet-Biedl, and nephronophthisis genes. Other systemic disorders associated with retinal degenerations that may also involve ciliary abnormalities include: Alstrom, Edwards-Sethi, Ellis-van Creveld, Jeune, Meckel-Gruber, Orofaciodigital Type 9, and Gurrieri syndromes. Understanding these conditions as ciliopathies may help the ophthalmologist to recognize associations between seemingly unrelated diseases and have a high degree of suspicion that a systemic finding may be present.

Refinement of the locus for autosomal recessive cone-rod dystrophy (CORD8) linked to chromosome 1q23-q24 in a Pakistani family and exclusion of candidate genes

Cone-rod retinal dystrophy (CORD) characteristically leads to early impairment of vision due to the simultaneous involvement of both cone and rod photoreceptor cells. Several loci/genes have been identified for CORD, including the cone-rod dystrophy (CORD8) locus [OMIM#605549] identified for a Pakistani family. All members of this family underwent detailed clinical re-examination to determine the nature of the dystrophy. All affected individuals suffered from bilateral CORD8 with an autosomal recessive mode of inheritance. The CORD8 locus, mapped on chromosome 1q12-q24, consisted of a very large critical disease region of 21 cM. Analysis with more recently available microsatellite markers within the reported region showed heterozygosity with some of the new markers, and the crossovers lead to a refinement of the disease region from 21 to 11.53 cM. Mutation screening has excluded some of the candidate genes in the region. The disease phenotype of this family could be due to a mutation in a novel gene located within the refined CORD8 locus.

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.

A detailed study of the phenotype of an autosomal dominant cone-rod dystrophy (CORD7) associated with mutation in the gene for RIM1

AIM

To characterise the phenotype of an autosomal dominant cone-rod dystrophy (CORD7) associated with the Arg844His mutation in RIM1.

METHODS

Eight members of a four generation, non-consanguineous British family were examined clinically and underwent electrophysiological testing, automated dark adapted perimetry, dark adaptometry, colour vision assessment, colour fundus photography, fundus fluorescein angiography (FFA), and fundus autofluorescence (AF) imaging.

RESULTS

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. The visual acuity ranged from 6/6 to 3/60. Colour vision testing showed mild to moderate dyschromatopsia in the majority of individuals. Fundus changes comprised a range of macular appearances varying from mild retinal pigment epithelial (RPE) disturbance to extensive atrophy and pigmentation. In some individuals retinal vessels were attenuated and in two subjects peripheral areas of retinal atrophy were present. An absent or severely reduced PERG was detected in all subjects, indicative of marked macular dysfunction. Full field ERG showed abnormal rod and cone responses. AF imaging revealed decreased macular AF centrally surrounded by a ring of increased AF in the majority of individuals. "Bull's eye" lesions were present in two individuals, comprising of a ring of decreased perifoveal AF bordered peripherally and centrally by increased AF. Photopic sensitivity testing demonstrated elevated central visual field thresholds with additional superior greater than inferior peripheral field loss. There were rod and cone sensitivity reductions in the central and peripheral visual fields, with the inferior retina being more affected than the superior.

CONCLUSIONS

The detailed phenotype is described of the autosomal dominant cone-rod dystrophy, CORD7, which is associated with a point mutation in RIM1, a gene encoding a photoreceptor synaptic protein. The pattern of disease progression and long term visual outcome facilitates improved genetic counselling and advice on prognosis. Such phenotypic data will be invaluable in the event of future therapy.

Clinical diagnoses that overlap with choroideremia

PURPOSE

To understand which clinical presentations suggest a diagnosis of choroideremia (CHM).

METHODS

Retrospective chart review. Included were patients for whom a clinical diagnosis of CHM was suggested, but either protein analysis or direct sequencing of the CHM gene could not confirm the diagnosis. Clinical presentation, family history and fundus photographs were reviewed.

RESULTS

We analyzed protein and DNA samples from members of more than 100 families in which at least 1 member had a clinical diagnosis of CHM. For 26 of these families, the clinical diagnosis of CHM could not be confirmed by laboratory analysis. Relevant clinical information was requested from the referring ophthalmologists so that alternative diagnoses could be considered. Sufficient information was provided for 13 of the 26 families. Four patients were reclassified as having retinitis pigmentosa (RP) from the clinical phenotype; only two clearly had X-linked inheritance. One patient had a syndrome including macular dystrophy, hearing loss, developmental delay and cerebral palsy. One patient was reclassified as having congenital stationary night blindness on the basis of an electronegative electroretinogram and a normal fundus. One patient had hearing loss suggesting Usher syndrome. One patient had signs consistent with cone-rod dystrophy (CRD). Five patients could not be reclassified on the basis of the clinical presentation.

CONCLUSION

RP, Usher syndrome and CRD are clinical phenotypes that may overlap with CHM. Clinical features that suggest CHM include severe chorioretinal atrophy with preservation of the macula, X-linked inheritance and retinal changes in a related female.

Identification of a locus on chromosome 2q11 at which recessive amelogenesis imperfecta and cone-rod dystrophy cosegregate

A consanguineous Arab pedigree in which recessive amelogenesis imperfecta (AI) and cone-rod dystrophy cosegregate, was screened for linkage to known retinal dystrophy and tooth abnormality loci by genotyping neighbouring microsatellite markers. This analysis resulted in linkage with a maximum lod score of 7.03 to the marker D2S2187 at the achromatopsia locus on chromosome 2q11, and haplotype analysis placed the gene(s) involved in a 2 cM/5 Mb interval between markers D2S2209 and D2S373. The CNGA3 gene, known to be involved in achromatopsia, lies in this interval but thorough analysis of its coding sequence revealed no mutation. Furthermore, affected individuals in four consanguineous recessive pedigrees with AI but without CRD were heterozygous at this locus, excluding it as a common cause of non-syndromic recessive AI. It remains to be established whether this pedigree is segregating two closely linked mutations causing disparate phenotypes or whether a single defect is causing pathology in both teeth and eyes.

Epidemiology of retinitis pigmentosa in Denmark

A nation-wide registration of Danish cases of retinitis pigmentosa (RP) provided 1890 persons diagnosed during the period 1850-1989. Prevalent at 1 January 1988 were 1301 persons (1:3943) comprising a multitude of different RP-types. Age specific prevalence rates demonstrated increasing rates of RP during the first four decades of life and a rather stable prevalence over the next 20-30 years. Corrected for incompleteness, a late decrease was found, reflecting an incomplete ascertainment of the oldest patients. A moving average method indicated an even later steady state value for the age-specific prevalence. The Danish prevalence figures were standardized according to the WHO World Standardized Prevalence Rates and compared with large studies from the USA and UK. No statistically significant difference was found. Usher syndrome was present in 12% of all RP-cases and Bardet-Biedl syndrome comprised 5%. Mental retardation was found in 144 cases (11%), mostly characterized by atypical RP. Nineteen per cent of patients affected by nonsystemic RP had an onset later than 30 years of age, whereas only a few per cent of persons with systemic RP had an RP onset after age 30 years. The Mendelian inheritance type of all cases was evaluated according to an unambiguous genetic classification, finding a larger amount of X-linked RP compared with other studies. Among nonsystemic RP-cases, 14.3% were found to be inherited as an X-linked trait whereas only 8.4% were autosomal dominantly inherited. The largest fraction was, as in previous materials, the simplex group (isolated cases) comprising 42.9% of the nonsystemic RP patients. Some factors influencing the results are discussed, with special emphasis on the problems associated with precise definitions of the Mendelian inheritance groups. A diagram according to the author's definition was constructed as a guideline ready for clinical application.

Biochemical analysis of a dimerization domain mutation in RetGC-1 associated with dominant cone-rod dystrophy

Mutations in the photoreceptor membrane guanylyl cyclase RetGC-1 have been linked to autosomal dominant cone-rod dystrophy. Three mutations were identified that alter strictly conserved residues within the RetGC-1 dimerization domain, a region predicted to form an amphipathic alpha-helical coil. Here we report on a biochemical characterization of one of the mutations, a substitution of cysteine for arginine at residue 838. We generated this mutation in vitro and measured its catalytic activity and sensitivity to guanylyl cyclase activating protein 1 (GCAP-1) and GCAP-2. The R838C substitution has several effects. It reduces the overall catalytic ability of RetGC-1 and dramatically reduces stimulation by GCAP-2, although GCAP-2 still appears to interact with the protein. The R838C substitution also increases the apparent affinity of RetGC-1 for GCAP-1 and alters the Ca(2+) sensitivity of the GCAP-1 response, allowing the mutant to be stimulated by GCAP-1 at higher Ca(2+) concentrations than wild type. The diminished response to GCAP-2, which we propose is not likely the cause of cone-rod degeneration in these patients, is interesting mechanistically because it separates the ability to bind a specific GCAP from the ability to be stimulated by it, and it also discriminates between the mechanisms of activation of GCAP-1 vs. GCAP-2. We suggest that the gain-of-function effects of R838C on RetGC-1 stimulated by GCAP-1, which are dominant in vitro and may cause an abnormal increase in cGMP synthesis in dark-adapted photoreceptors, may be the cause of the cone-rod degeneration.

Clinical and genetic studies of an autosomal dominant cone-rod dystrophy with features of Stargardt disease

Cone-rod dystrophy (CORD) and Stargardt disease (STGD) are two hereditary retinal dystrophies with similarities to age-related macular degeneration. Cone-rod dystrophies are a group of degenerative disorders resulting in decreased visual acuity and color vision, attenuated electroretinographic (ERG) responses, and atrophic macular lesions. Autosomal dominant, autosomal recessive, and X-linked forms of cone-rod dystrophy have been reported. Stargardt disease is characterized by reduced visual acuity, atrophic macular changes, prominent 'flavimaculatus flecks' in the pigment epithelium of the posterior retina, and a virtually pathognomic 'dark choroid' pattern on fluorescein angiography. Stargardt disease is classically inherited as an autosomal recessive trait, although numerous families have been described in which features of Stargardt disease are transmitted in an autosomal dominant manner. We have identified a new kindred with autosomal dominant cone-rod dystrophy with features of Stargardt-like disease. Detailed clinical evaluation, genotype analysis, and linkage analysis were performed. Fluorescein angiography revealed a 'dark choroid' pattern in three affected subjects. Electroretinography disclosed markedly reduced scotopic and photopic responses in three affected individuals. Genetic analysis revealed linkage to known loci for cone-rod dystrophy (CORD7) and Stargardt-like disease (STGD3) on chromosome 6q14. A peak lod score of 3.3 was obtained with the marker D6S280 at straight theta =0.010. A physical map was constructed by screening a YAC library with short tandem repeat markers in the region. Screening of a candidate gene, the rho1 subunit of the GABA receptor, failed to reveal any mutations.

The cone dystrophies

The cone dystrophies are a heterogeneous group of inherited disorders that result in dysfunction of the cone photoreceptors and sometimes their post-receptoral pathways. The major clinical features of cone dystrophy are photophobia, reduced visual acuity and abnormal colour vision. Ganzfeld electroretinography shows reduced or absent cone responses. On the basis of their natural history, the cone dystrophies may be broadly divided into two groups: stationary and progressive cone dystrophies. The stationary cone dystrophies have received more attention, and subsequently our knowledge of their molecular genetic, psychophysical and clinical characteristics is better developed. Various methods of classification have been proposed for the progressive cone dystrophies, but none is entirely satisfactory, largely because the underlying disease mechanisms are poorly understood. Multidisciplinary studies involving clinical assessment, molecular genetics, electrophysiology and psychophysics should lead to an improved understanding of the pathogenesis of these disorders.

A new family of Greek origin maps to the CRD locus for autosomal dominant cone-rod dystrophy on 19q

Retinal photoreceptor dystrophies (RD) are a highly heterogeneous group of genetic disorders of the retina, representing the most frequently inherited form of visual handicap, affecting approximately 1.5 million people world wide. To date, more than 40 genetic loci have been implicated in RD. One of them, the CORD2 locus, for an autosomal dominant form of cone-rod dystrophy (CRD), maps to chromosome 19q and has previously been reported in a single large family of British origin. We now report a new family with severe early onset CRD, phenotypically very similar to the British family, which also maps to 19q, but is of Greek origin. Haplotype data of the Greek family showed no recombination between and including markers D19S219 and D19S246 and linkage analysis gave a lod score of 2.7 (at theta=0) with marker D19S412, confirming the data obtained in the British family.

Molecular genetics of central retinal dystrophies

A range of chorioretinal dystrophies that principally affect the central retina have recently been associated with either specific genetic mutations or mapped to refined genomic loci. Mutations of two genes, peripherin/RDS (chromosome 6p) and TIMP3 (chromosome 22q) have been shown to be of particular importance to this group of disorders. Other conditions such as Stargardt's disease, Best's disease, pattern dystrophy, cone dystrophy and cone-rod dystrophy have been mapped to different regions of the genome, however the underlying genetic mutations await identification. Molecular genetic diagnostic techniques are now available for a number of central choroidoretinal dystrophies allowing for earlier, accurate diagnosis and laying the groundwork for future studies of potential therapeutic protocols.

Design for slides

The basic principles of design for projection slides are discussed, with particular reference to the impact of the personal computer and commercial presentation software on the material that is destined to end up on the screen at meetings and in seminar rooms. While modern software can be a boon to the presenter, allowing simple creation of slides, it can also encourage some of the worst excesses. The keynote of the design of slides for educational purposes should be simplicity, and ways of achieving simple but effective results are described.

Genetic linkage of cone-rod retinal dystrophy to chromosome 19q and evidence for segregation distortion

Inherited retinal dystrophies are the most common cause of childhood blindness in the developed world. Cone-rod retinal dystrophies are severe examples of this group of disorders. Analysis of a large cone-rod dystrophy pedigree suggested that inheritance within the family was influenced by meiotic drive (p = 0.008), a rare segregation distortion in human genetics. Two-point linkage analysis showed significant linkage with three markers mapping to chromosome 19q. Multipoint analysis gave a maximum lod score of 10.08 (theta = 0.05) distal to D19S47. Cone-rod dystrophy is therefore assigned to 19q13.1-q13.2 and a new candidate locus for other retinal dystrophies is identified.

Retinitis pigmentosa and allied disorders in Denmark. IV. Ophthalmic features in systemic and non-systemic cases

We analyzed the composition of a retinitis pigmentosa (RP) sample with respect to clinical appearance. The material included 1301 affected persons derived from a national Danish survey with a high degree of completeness. The cases were grouped according to ocular signs and symptoms into typical RP, atypical RP, vitreoretinal RP, chorioretinal dystrophy, and unclassified. The relative frequency with which these groups were nosologically allocated to systemic and non-systemic retinitis pigmentosa is presented. Among 837 cases of non-systemic RP 60% had ophthalmoscopic abnormalities and visual symptoms in accordance with typical RP, 29% were characterized as atypical and 6% presented with chorioretinal dystrophy. The results of earlier epidemiological studies, sex distribution, and new diagnostic concepts based on DNA analysis are discussed.