Macular Degeneration: Webster AR

Ziskind A, Bardien S, van der Merwe L, Webster AR. · Division of Ophthalmology, Faculty of Health Sciences, University of Stellenbosch, Cape Town, South Africa. · Ophthalmic Genet. · Pubmed #18766990 No free full text.

Abstract: The H402 allele of the CFH gene is an established risk factor for age-related maculopathy (ARMD) in Caucasians, accounting for approximately 60% of the genetic risk at the population level. In general, the advanced forms of ARMD are rare in Black populations in Africa, as well as Black populations who have lived for generations in the United States or the West Indies, although there are reports that the earlier forms such as drusen may not be all that uncommon. The aim of the present study was to estimate the frequency of the C allele of the CFH Y402H variant in an aged South African Black Xhosa population and to describe the evidence of ARMD found.

Hornan DM, Peirson SN, Hardcastle AJ, Molday RS, Cheetham ME, Webster AR. · Institute of Ophthalmology, Molecular Genetics, University College, London, United Kingdom. · Invest Ophthalmol Vis Sci. · Pubmed #18055785 links to  free full text

Abstract: PURPOSE: The macula is essential for visual acuity. It contains many more cone photoreceptors than does the peripheral retina. In this study, macular gene expression was compared with that in the rod-rich peripheral retina. METHODS: Two-millimeter foveomacular and four-millimeter macular punches from human donor eyes, in addition to sections of midperipheral retina, were used to study differential gene expression. Multiple microarray experiments were combined with quantitative PCR and bioinformatic analyses. In the present study, the expression of both known and previously unidentified retinal genes was determined. RESULTS: Several macula enriched transcripts were revealed. Nuclear pore complex interacting protein (NPIP) and eukaryotic translation initiation factor 2alpha kinase (GCN2) were expressed at levels approaching that of red/green cone opsin in the macula. The protein products of several genes highlighted using these expression analyses were also localized in the retina. Both NPIP and histone deacetylase 9 (HDAC9) proteins were detected in cone photoreceptor outer segments. CONCLUSIONS: Characterizing macula enriched transcripts is an important stepping-stone in understanding the molecular basis for visual acuity in the retina. The approach also provides excellent candidates for diseases that affect the macula and fovea such as age-related macular degeneration (AMD). Indeed, several of these transcripts, such as NPIP and GCN2, have genomic loci that are consistent with being candidate genes for AMD.

Audo I, Vanakker OM, Smith A, Leroy BP, Robson AG, Jenkins SA, Coucke PJ, Bird AC, De Paepe A, Holder GE, Webster AR. · Laboratoire de Physiopathologie Cellulaire Moléculaire et de la Rétine, Institut National de la Santé et de la Recherche Médicale, Université Pierre et Marie Curie, Paris, France. · Invest Ophthalmol Vis Sci. · Pubmed #17724214 links to  free full text

Abstract: PURPOSE: Pseudoxanthoma elasticum (PXE; [MIM 264800]) is an autosomal recessive systemic disorder characterized by progressive degeneration and calcification of elastic fibers in connective tissue. The phenotype is variable, with cutaneous, vascular, and ophthalmic abnormalities. The disorder is a consequence of mutations in the ABCC6 gene. Visual impairment is mainly due to neovascular complications, and retinal function is usually assumed to be normal. The purpose of this study was the objective assessment of macular and generalized retinal function in unrelated patients with clinical and/or genetic features of PXE. METHODS: Four unrelated patients carrying a clinical diagnosis of PXE presented with unexplained visual loss. After ophthalmic examination, retinal and macular function was assessed by full-field electroretinogram (ERG) and pattern ERG, respectively, according to ISCEV (International Society for Clinical Electrophysiology of Vision) recommendations. Molecular analysis of the ABCC6 gene was performed in three patients by dHPLC (denaturing high-performance liquid chromatography) and direct sequencing. RESULTS: Full-field ERG revealed significant reduction of cone and rod responses in all four patients. Funduscopic appearances varied. Three patients were found to carry ABCC6 mutations. In case 1, a novel nonsense mutation (p.L1474X) was detected in exon 31 paired with a splice-site mutation. Mutation analyses in cases 3 and 4 revealed previously reported ABCC6 mutations. CONCLUSIONS: These findings suggest that retinal dysfunction in PXE may not be uncommon. The mechanism underlying retinal dysfunction is unknown but may result from metabolic disturbance leading to retinal toxicity with a possible role of modifying genetic or environmental factors rather than specific ABCC6 mutations.

Sivaprasad S, Adewoyin T, Bailey TA, Dandekar SS, Jenkins S, Webster AR, Chong NV. · Laser and Retinal Research Unit, King's College Hospital, King's College London, England. · Arch Ophthalmol. · Pubmed #17420372 links to  free full text

Abstract: OBJECTIVES: To determine the role of systemic complement activation in the pathogenesis of age-related macular degeneration and to examine whether serum C3a des Arg reflects systemic complement activation, independent of individual complement component levels. METHODS: Plasma complement C3a des Arg levels and a single nucleotide polymorphism at position 402 of the complement factor H gene (CFH) were determined in 3 groups of subjects: 42 subjects with early age-related maculopathy, 42 subjects with neovascular (wet) age-related macular degeneration, and a control group of 38 subjects with no clinical evidence of age-related changes at the macula. RESULTS: The median (range) of plasma complement C3a des Arg levels in the age-related maculopathy and neovascular age-related macular degeneration groups were 52.6 (2.8-198.1) ng/mL and 60.9 (3.1-173.1) ng/mL, respectively. The levels were significantly raised compared with the control group (n = 38), which had a median (range) plasma complement C3a des Arg level of 40.3 (6.1-81.7) ng/mL (analysis of variance, P = .02). The concentration of plasma C3a des Arg did not differ significantly between those with different CFH genotypes (P = .07). CONCLUSION: Systemic activation of the complement system may contribute to the pathogenesis of age-related macular degeneration independent of CFH polymorphism. CLINICAL RELEVANCE: The results of this study may be relevant to aiming new treatment strategies toward reducing systemic low-grade inflammation.

Tschernutter M, Jenkins SA, Waseem NH, Saihan Z, Holder GE, Bird AC, Bhattacharya SS, Ali RR, Webster AR. · Institute of Ophthalmology, Bath Street, London EC1V 9EL, UK. · Br J Ophthalmol. · Pubmed #16714263 links to  free full text

Abstract: BACKGROUND/AIM: MERTK, a tyrosine kinase receptor protein expressed by the retinal pigment epithelium (RPE), is mutated in both rodent models and humans affected by retinal disease. This study reports a survey of families for Mertk mutations and describes the phenotype exhibited by one family. METHODS: 96 probands with retinal dystrophy, consistent with autosomal recessive segregation, were screened by direct sequencing. A family homozygous for a likely null allele was investigated clinically. RESULTS: A novel frame shifting deletion was identified in one of 96 probands. Other polymorphisms were detected. The deletion allele occurred on both chromosomes of four affected family members. Electrophysiology demonstrated early loss of scotopic and macular function with later loss of photopic function. Visual acuities and visual fields were preserved into the second decade. Perception of light vision was present in a patient in the fourth decade. A "bull's eye" appearance and a hyperautofluorescent lesion at the central macula were consistent clinical findings. CONCLUSIONS: Mutations in Mertk are a rare cause of ARRP in humans. The study extends the phenotypic characteristics of this retinal dystrophy and shows distinctive clinical signs that may improve its clinical identification. The moderate severity and presence of autofluorescence implies that outer segment phagocytosis is not entirely absent.

Dandekar SS, Jenkins SA, Peto T, Bird AC, Webster AR. · Professorial Unit, Moorfields Eye Hospital, 162 City Road, London EC1V 2PD, UK. · Br J Ophthalmol. · Pubmed #16597668 links to  free full text

Abstract: AIMS: To assess the influence of smoking on the type of age related macular degeneration (AMD) lesion causing visual impairment in a large cohort of patients with AMD at a tertiary referral UK centre. METHODS: Prospective, observational, cross sectional study to analyse smoking data on 711 subjects, of western European origin, in relation to the type of AMD lesion present. Colour fundus photographs were graded according to a modified version of the international classification. Multiple logistic regression analysis was performed, adjusting for age and sex using the statistical package SPSS ver 9.0 for Windows. chi(2) tests were also used to assess pack year and ex-smoker data. RESULTS: 578 subjects were graded with neovascular AMD and 133 with non-neovascular AMD. There was no statistically significant association found between smoking status or increasing number of pack years and type of AMD lesion. The odds of "current smokers" compared to "non-smokers" developing neovascular rather than non-neovascular AMD when adjusted for age and sex was 1.88 (95% CI: 0.91 to 3.89; p = 0.09). CONCLUSIONS: Smoking is known to be a risk factor for AMD and this study suggests that smokers are at no more risk of developing neovascular than atrophic lesions.

Dandekar SS, Jenkins SA, Peto T, Scholl HP, Sehmi KS, Fitzke FW, Bird AC, Webster AR. · Moorfields Eye Hospital and Institute of Ophthalmology, London, England. · Arch Ophthalmol. · Pubmed #16286612 No free full text.

Abstract: OBJECTIVE: To describe the autofluorescence (AF) characteristics of choroidal neovascularization (CNV) in patients with age-related macular degeneration. METHODS: Autofluorescence images of 65 consecutive eyes with CNV at various stages of evolution were analyzed. Twenty images were of recent-onset CNV (group 1), 8 were of eyes 1 to 6 months after CNV diagnosis (group 2), and 37 were late-stage CNV (group 3). Autofluorescence images from groups 1 and 2 were compared with fundus fluorescein angiographic images. RESULTS: Group 1 showed areas of hyperfluorescence on fundus fluorescein angiography corresponding to areas of normal AF in 16 of 20 cases, with adjacent areas of increased AF in 13 cases. The main areas of abnormal AF were larger than the main areas of abnormal fluorescence on fundus fluorescein angiography in 18 of the 20 cases. Groups 2 and 3 showed areas of decreased AF corresponding to areas of previous leakage on fundus fluorescein angiography (in group 2) or atrophy. CONCLUSIONS: Preserved AF in group 1 indicates viable retinal pigment epithelium initially, which has implications for visual prognosis. Decreased AF in groups 2 and 3 indicates loss of retinal pigment epithelium and photoreceptors. Autofluorescence imaging may increase our understanding of CNV in age-related macular degeneration.

Michaelides M, Wilkie SE, Jenkins S, Holder GE, Hunt DM, Moore AT, Webster AR. · Institute of Ophthalmology, University College London, London, United Kingdom. · Ophthalmology. · Pubmed #15953638 No free full text.

Abstract: PURPOSE: To determine the underlying molecular genetic basis of a retinal dystrophy identified in a 4-generation family and to examine the phenotype and the degree of intrafamilial variability. DESIGN: Prospective case series. PARTICIPANTS: Six affected individuals from a nonconsanguineous British family. METHODS: Detailed ophthalmologic examination, color fundus photography, autofluorescence imaging, and electrophysiologic assessment were performed. Blood samples were taken for DNA extraction, and mutation screening of GUCA1A, the gene encoding guanylate cyclase-activating protein 1 (GCAP1), was undertaken. RESULTS: All affected subjects complained of mild photophobia and reduced central and color vision. Onset was between the third and fifth decade, with subsequent gradual deterioration of visual acuity and color vision. Visual acuity ranged between 6/9 and counting fingers. Color vision was either absent or markedly reduced along all 3 color axes. A range of macular appearances was seen, varying from mild retinal pigment epithelial disturbance to extensive atrophy. Electrophysiologic testing revealed a range of electrophysiologic abnormalities: isolated cone electroretinography abnormalities, reduced cone and rod responses (with cone loss greater than rod), and isolated macular dysfunction. The 4 coding exons of GUCA1A were screened for mutations in affected and unaffected family members. A single transition, A319G, causing a nonconservative missense substitution, Tyr99Cys, segregated uniquely in all affected subjects. CONCLUSIONS: The Tyr99Cys GUCA1A mutation has been previously shown to cause autosomal dominant progressive cone dystrophy. This is the first report of this mutation also causing both cone-rod dystrophy and isolated macular dysfunction. The phenotypic variation described here exemplifies the intrafamilial heterogeneity of retinal dysfunction that can be observed in persons harboring the same mutation and chromosomal segment.

Ebenezer ND, Michaelides M, Jenkins SA, Audo I, Webster AR, Cheetham ME, Stockman A, Maher ER, Ainsworth JR, Yates JR, Bradshaw K, Holder GE, Moore AT, Hardcastle AJ. · Division of Molecular Genetics, University College London, UK. · Invest Ophthalmol Vis Sci. · Pubmed #15914600 links to  free full text

Abstract: PURPOSE: To test the incidence of mutations in RPGR ORF15 in six families with X-linked progressive retinal degeneration (cone-rod dystrophy [XLCORD], macular or cone dystrophy) and to undertake a detailed phenotypic assessment of families in whom ORF15 mutations were identified. METHODS: To amplify and sequence ORF15 in its entirety, a cloning strategy was developed. Families with mutations in ORF15 underwent electrophysiological testing, color vision assessment, color fundus photography, and fundus autofluorescence (AF) imaging. RESULTS: Novel protein truncation mutations were identified in two families. In family A, a 2-bp mutation was identified in ORF15+A1094C G1095T, predicted to result in a truncated protein (E364D/E365X). In family B, a G-to-T transversion (ORF15+1176G>T) resulted in a nonsense mutation (G392X). Characteristics of phenotype in both families included progressive deterioration of central vision and subsequently night vision, mild photophobia, and moderate to high myopia. Ophthalmoscopic abnormalities were generally confined to the macula. A parafoveal ring of increased AF was observed, and electrophysiological evidence of a greater generalized abnormality in cone than rod responses were consistent with a cone-rod dystrophy phenotype. CONCLUSIONS: The cloning strategy for ORF15 facilitated comprehensive sequence analysis in patients. Two families were identified with nonsense mutations, and clinical evaluation revealed them both to have a similar phenotype. The presence of a parafoveal ring of increased AF was an early indicator of affected status in these families. No disease-causing mutations in ORF15 were detected in four other families, suggesting that ORF15 mutations may not be the most common cause of XLCORD.

Hammond CJ, Webster AR, Snieder H, Bird AC, Gilbert CE, Spector TD. · Twin Research and Genetic Epidemiology Unit, St. Thomas' Hospital, Lambeth Palace Road, London SE1 7EH, England, UK. · Ophthalmology. · Pubmed #11927430 No free full text.

Abstract: OBJECTIVE: Age-related macular degeneration (AMD) is the most common cause of blindness in industrialized countries. There has been considerable interest in the genetics of early age-related maculopathy (ARM) and AMD, because they have phenotypes similar to inherited diseases where mutations have been identified, but the heritability of ARM and AMD is unknown. DESIGN: A classical twin study was performed to compare the concordance in monozygotic (MZ) and dizygotic (DZ) twins in an unselected sample of female volunteer twins. PARTICIPANTS: Five hundred six twin pairs, 226 MZ and 280 DZ, with a mean age of 62 years, were examined. METHODS: ARM was graded from stereoscopic macular photographs of 501 of the twin pairs (99%) according to the International ARM Epidemiologic Study Group grading system. The casewise concordance was calculated for twin pairs from 2 x 2 contingency tables of affected/unaffected twins, and these tables were used in maximum likelihood genetic modeling to estimate the heritabilities of phenotypes graded. MAIN OUTCOME MEASURES: Prevalence of ARM; concordance in MZ and DZ twins of the phenotypes of ARM, soft drusen >63 microm and > or =125 microm diameter, pigmentary changes and hard drusen (<20 and > or =20 in number); heritability of ARM and subphenotypes. RESULTS: The overall prevalence of ARM was 14.6% (95% confidence interval [CI], 12.4%-16.8%). The concordance for ARM in MZ twins was 0.37 compared with 0.19 in DZ twins, suggesting a role for genes. Modeling confirmed a genetic effect for phenotypes of ARM, soft drusen, pigmentary changes, and > or =20 hard drusen, although there was little genetic effect for scattered (<20) hard drusen. The heritability of ARM was estimated as 45% (95% CI, 35%-53%). The most heritable phenotypes were soft drusen > or =125 microm (57%) and > or =20 hard drusen (81%), with the latter being dominantly inherited. CONCLUSIONS: This study confirms a significant genetic influence in ARM and suggests that future genetic studies should examine phenotypes of large (> or =125 microm) soft drusen and > or =20 hard drusen, because these seem to be the most heritable components.

Webster AR, Héon E, Lotery AJ, Vandenburgh K, Casavant TL, Oh KT, Beck G, Fishman GA, Lam BL, Levin A, Heckenlively JR, Jacobson SG, Weleber RG, Sheffield VC, Stone EM. · Department of Ophthalmology, The University of Iowa College of Medicine, 200 Hawkins Drive, Iowa City, IA 52242, USA. · Invest Ophthalmol Vis Sci. · Pubmed #11328725 links to  free full text

Abstract: PURPOSE. To assess the allelic variation of the ATP-binding transporter protein (ABCA4). METHODS. A combination of single-strand conformation polymorphism (SSCP) and automated DNA sequencing was used to systematically screen this gene for sequence variations in 374 unrelated probands with a clinical diagnosis of Stargardt disease, 182 patients with age-related macular degeneration (AMD), and 96 normal subjects. RESULTS. There was no significant difference in the proportion of any single variant or class of variant between the control and AMD groups. In contrast, truncating variants, amino acid substitutions, synonymous codon changes, and intronic variants were significantly enriched in patients with Stargardt disease when compared with their presence in subjects without Stargardt disease (Kruskal-Wallis P < 0.0001 for each variant group). Overall, there were 2480 instances of 213 different variants in the ABCA4 gene, including 589 instances of 97 amino acid substitutions, and 45 instances of 33 truncating variants. CONCLUSIONS. Of the 97 amino acid substitutions, 11 occurred at a frequency that made them unlikely to be high-penetrance recessive disease-causing variants (HPRDCV). After accounting for variants in cis, one or more changes that were compatible with HPRDCV were found on 35% of all Stargardt-associated alleles overall. The nucleotide diversity of the ABCA4 coding region, a collective measure of the number and prevalence of polymorphic sites in a region of DNA, was found to be 1.28, a value that is 9 to 400 times greater than that of two other macular disease genes that were examined in a similar fashion (VMD2 and EFEMP1).