Macular Degeneration: Allikmets R

Allikmets R. · Departments of Ophthalmology and Pathology, Columbia University, New York, NY 10032, USA. · Am J Hum Genet. · Pubmed #10970771 links to  free full text

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Allikmets R. · No affiliation provided · Eur J Ophthalmol. · Pubmed #10651188 No free full text.

Abstract: Age-related macular degeneration (AMD), a multifactorial human disorder, is the most common cause of acquired visual impairment in people over the age 60. It is estimated to affect millions of individuals worldwide. Prevalence increases with age; among persons 75 years and older, mild, or early forms occur in nearly 30% and advanced forms in about 7% of the population. AMD has been associated both with environmental and genetic factors. However, the clinical heterogeneity, late age at onset, and complex etiology have confounded genetic studies of the disorder. Methods applicable to the study of single-gene and some complex disorders (i.e., linkage analysis, sib-pair analysis, transmission disequilibrium test, etc.) have had limited utility in elucidating the genetic components of the complex AMD trait. Recently, substantial progress has been made in determining the genetic basis of monogenic eye disorders. On a monthly basis mutations are identified in new genes responsible for some form of retinal degeneration. Most, if not all, of these genes become candidates for potential involvement in multifactorial disorders especially if the phenotypes of the early-onset Mendelian diseases they cause resemble later onset complex traits. Unfortunately, to date mutational analyses of the candidate genes in AMD patients to date have not yielded the highly anticipated information: statistically significant association of sequence variants with AMD. Whether this is due to the unsuccessful selection of the right candidate genes for the analysis, or the methods employed, or both, has to be elucidated. This review summarizes current knowledge of genetic research aimed at delineating the molecular genetic basis of age-related macular degeneration. Moreover, it attempts to offer some approaches for the future studies directed towards understanding the genetic components of this complex disorder.

Klaver CC, Allikmets R. · Department of Ophthalmology, Columbia University, New York, N.Y., USA. · Dev Ophthalmol. · Pubmed #12876836 No free full text.

Abstract: Determining the genetic component of the age-related macular degeneration (AMD) complex trait has been the primary goal of ophthalmic genetics research for almost a decade. During this time, genes of several Mendelian traits affecting the macula have been identified. In this review, we will discuss the consequences of molecular defects in the VMD2, EFEMP1, TIMP3, ELOVL4 and ABCA4 genes, and their association with macular disease. We will also analyze our current knowledge on the implications of genetic variations in these genes for AMD by summarizing data from all studies which have investigated the possible role of these candidate genes in the etiology of AMD. Finally, we will elaborate on methods for genetic dissection of complex traits and discuss the appropriate applications of these methods for identifying genetic determinants of AMD.

Shroyer NF, Lewis RA, Allikmets R, Singh N, Dean M, Leppert M, Lupski JR. · Program in Cell and Molecular Biology, Baylor College of Medicine, Houston, TX 77030, USA. · Vision Res. · Pubmed #10396622 No free full text.

Abstract: The ABCR gene encodes a rod photoreceptor specific ATP-binding cassette transporter. Mutations in ABCR are associated with at least four inherited retinal dystrophies: Stargardt disease, Fundus Flavimaculatus, cone-rod dystrophy, and retinitis pigmentosa. A statistically significant increase in heterozygous ABCR alterations has been identified in patients with age-related macular degeneration (AMD). A pedigree is described which manifests both Stargardt disease and AMD in which an ABCR mutation cosegregates with both disease phenotypes. These data from this case report support the hypothesis that ABCR is a dominant susceptibility locus for AMD. Recent work regarding ABCR is reviewed and a model is presented in which decreased ABCR function correlates with severity of retinal disease.

Ferrara DC, Merriam JE, Freund KB, Spaide RF, Takahashi BS, Zhitomirsky I, Fine HF, Yannuzzi LA, Allikmets R. · LuEsther T. Mertz Retinal Research Center, New York, New York, USA. · Arch Ophthalmol. · Pubmed #19001225 No free full text.

Abstract: OBJECTIVE: To analyze the frequency of major age-related macular degeneration (AMD)-associated alleles in patients with multifocal choroiditis (MFC). METHODS: A cohort of 48 patients with MFC was compared with previously characterized cohorts of patients with advanced AMD (368 samples) and matched unaffected controls (368 samples). Allele and genotype frequencies of single nucleotide polymorphisms for the following AMD-associated alleles were evaluated: risk alleles in complement factor H (CFH) gene (Y402H and IVS14) and LOC387715/HTRA1 gene on 10q26 (A69S) and protective alleles in CFH (IVS1, IVS6, and delCFHR1-3) and complement factor B loci (H9L and R32Q). RESULTS: Frequencies of all major AMD-associated alleles in the CFH locus indicate a strong, statistically significant association of CFH gene single nucleotide polymorphisms and MFC. However, the same analysis for the single nucleotide polymorphisms in complement factor B and 10q26 loci matched the results in the control group. CONCLUSIONS: Like AMD, the MFC phenotype is strongly associated with the major alleles/haplotypes in the CFH locus. Clinical Relevance We report compelling evidence of a strong association between CFH polymorphisms and MFC, which contributes to the understanding of MFC pathogenesis and suggests new potential therapeutic targets.

Hwang JC, Zernant J, Allikmets R, Barile GR, Chang S, Smith RT. · Department of Ophthalmology, Columbia University, New York, New York 10032, USA. · Retina. · Pubmed #18854780 No free full text.

Abstract: OBJECTIVE: To demonstrate that Stargardt disease (STGD) can present with peripapillary atrophy. METHODS: Retrospective case series. The medical records of 150 consecutive patients (300 eyes) were reviewed retrospectively from a STGD database from January 1999 to May 2007 at Columbia University's Harkness Eye Institute. STGD patients demonstrating peripapillary atrophy were identified. RESULTS: Three of 150 cases of STGD (2.0%) demonstrated peripapillary atrophy. Case 1 revealed peripapillary and central atrophy with heterozygous ABCA4 mutations P1380L and IVS40 + 5G>A. Case 2 demonstrated atrophic fleck lesions involving the peripapillary region and central atrophy with homozygous ABCA4 mutations P1380L and P1380L. Case 3 revealed bilateral central atrophy and pisciform fleck atrophy involving the peripapillary, macular, and peripheral regions with ABCA4 mutations P1380L and R2030Q. Overall, ABCA4 mutation P1380L was noted in 13 cases (8.7%), IVS40 + 5G>A in 6 cases (4.0%), and R2030Q in 1 case (0.7%). The remaining cases shared one common STGD mutation with Case 1, 2, and 3 (P1380L or IVS40 + 5G>A) and demonstrated classic STGD findings of central atrophy and varying presence of peripheral flecks without peripapillary lesions. CONCLUSION: STGD can present with peripapillary atrophy. This relatively uncommon phenotype may arise from specific combinations of STGD ABCA4 mutations rather than single mutations.

Tsang SH, Tsui I, Chou CL, Zernant J, Haamer E, Iranmanesh R, Tosi J, Allikmets R. · Bernard and Shirlee Brown Glaucoma Laboratory, Department of Pathology and Cell Biology, Columbia University, New York, New York, USA. · Am J Ophthalmol. · Pubmed #18723146 No free full text.

Abstract: PURPOSE: To develop a systematic approach for the molecular diagnosis of retinitis pigmentosa (RP) and to report new genotype-phenotype correlations for phosphodiesterase 6 (PDE6)-based RP mutations. DESIGN: Clinical and molecular studies on a retrospective case series. METHODS: We screened 40 unrelated RP patients with an autosomal recessive RP microarray. Individuals with RP caused by PDE6 deficiency underwent genetic segregation and phenotype analysis. RESULTS: A disease-associated allele was identified in 32% of patients. Two probands (5%) had PDE6 mutations. The first proband was a compound heterozygote for known R102C and N216S alleles in PDE6A (MIM#180071). Pedigree analysis determined that the N216S variant was benign and direct sequencing discovered a novel, S303C allele. The second proband had a homozygous D600N mutation in the PDE6B gene (MIM#180072). Visual acuities of PDE6-deficient patients ranged from 20/40 to 20/200. Clinical studies showed unusual vitreomacular traction, cystoid macular edema, macular atrophy, and ring hyperfluorescence in PDE6-deficient patients. Such extensive vitreoretinal degeneration is not characteristic of photoreceptor-specific enzyme deficiencies. CONCLUSION: High-throughput deoxyribonucleic acid microarray chips can be used in combination with clinical imaging to precisely characterize patients with RP. Identifying the precise mutation in RP may become the standard of care as gene therapy emerges.

Barbazetto IA, Room M, Yannuzzi NA, Barile GR, Merriam JE, Bardal AM, Freund KB, Yannuzzi LA, Allikmets R. · Department of Ophthalmology, Columbia University, New York, New York, USA. · Invest Ophthalmol Vis Sci. · Pubmed #18502988 No free full text.

Abstract: PURPOSE: To investigate the prevalence of sequence variants in the ATM gene and to determine the frequency of major age-related macular degeneration (AMD)-associated variants in CFH, CFB, and 10q26 loci in patients with idiopathic perifoveal telangiectasia (IPT). METHODS: Thirty patients with diagnoses of IPT underwent standard ophthalmologic evaluation that included visual acuity testing, fundus photography, and fluorescein angiography. DNA was screened for variations in the ATM gene by a combination of denaturing high-performance liquid chromatography and direct sequencing. Major AMD-associated alleles in CFH, CFB, and 10q loci were screened by PCR-restriction fragment-length polymorphism. RESULTS: Nineteen female and 11 male patients (average age, 59 years) with a median visual acuity of 20/50 were evaluated. Six patients were of Asian-Indian origin, one was Hispanic, and 23 were of European-American ancestry. Nine of 30 (30%) patients had diabetes mellitus, 18 of 30 (60%) patients had hypertension, and 12 of 30 (40%) patients had a history of smoking. Screening of the ATM gene revealed a null allele in 2 of 23 (8.7%) patients of European ancestry, previously disease-associated missense alleles in 4 of 23 (17.4%) patients, and common missense alleles in 7 of 23 (30.4%) patients. No variants were identified in the ATM gene in patients of Asian or Hispanic origin. Frequencies of major AMD-associated alleles in CFH, CFB, and 10q loci in the IPT cohort were similar to those in the ethnically matched general population. CONCLUSIONS: At least 26%, and maybe up to 57%, of IPT patients of European-American descent carried possibly disease-associated ATM alleles. Vascular risk factors such as hypertension, diabetes, and smoking may be associated with the pathogenesis of the disease.

Despriet DD, Bergen AA, Merriam JE, Zernant J, Barile GR, Smith RT, Barbazetto IA, van Soest S, Bakker A, de Jong PT, Allikmets R, Klaver CC. · Department of Clinical and Molecular Ophthalmogenetics, Netherlands Institute for Neuroscience, Royal Netherlands Academy of Arts and Sciences (KNAW), Amsterdam, The Netherlands. · Invest Ophthalmol Vis Sci. · Pubmed #18172114 links to  free full text

Abstract: PURPOSE: To determine whether variants in the candidate genes TLR4, CCL2, and CCR2 are associated with age-related macular degeneration (AMD). METHODS: This study was performed in two independent Caucasian populations that included 357 cases and 173 controls from the Netherlands and 368 cases and 368 controls from the United States. Exon 4 of the TLR4 gene and the promoter, all exons, and flanking intronic regions of the CCL2 and CCR2 genes were analyzed in the Dutch study and common variants were validated in the U.S. study. Quantitative (q)PCR reactions were performed to evaluate expression of these genes in laser-dissected retinal pigment epithelium from 13 donor AMD and 13 control eyes. RESULTS: Analysis of single nucleotide polymorphisms (SNPs) in the TLR4 gene did not show a significant association between D299G or T399I and AMD, nor did haplotypes containing these variants. Univariate analyses of the SNPs in CCL2 and CCR2 did not demonstrate an association with AMD. For CCR2, haplotype frequencies were not significantly different between cases and controls. For CCL2, one haplotype containing the minor allele of C35C was significantly associated with AMD (P = 0.03), but this did not sustain after adjustment for multiple testing (q = 0.30). Expression analysis did not demonstrate altered RNA expression of CCL2 and CCR2 in the retinal pigment epithelium from AMD eyes (for CCL2 P = 0.62; for CCR2 P = 0.97). CONCLUSIONS: No evidence was found of an association between TLR4, CCR2, and CCL2 and AMD, which implies that the common genetic variation in these genes does not play a significant role in the etiology of AMD.

Hageman GS, Hancox LS, Taiber AJ, Gehrs KM, Anderson DH, Johnson LV, Radeke MJ, Kavanagh D, Richards A, Atkinson J, Meri S, Bergeron J, Zernant J, Merriam J, Gold B, Allikmets R, Dean M, Anonymous00181. · Department of Ophthalmology and Visual Sciences, Cell Biology and Functional Genomics Laboratory, The University of Iowa, 11190E PFP, 200 Hawkins Drive, Iowa City, Iowa 52240, USA. · Ann Med. · Pubmed #17438673 links to  free full text

Abstract: BACKGROUND: Variants in the complement factor H gene (CFH) are associated with age-related macular degeneration (AMD). CFH and five CFH-related genes (CFHR1-5) lie within the regulators of complement activation (RCA) locus on chromosome 1q32. Aims and Methods. In this study, the structural and evolutionary relationships between these genes and AMD was refined using a combined genetic, molecular and immunohistochemical approach. RESULTS: We identify and characterize a large, common deletion that encompasses both the CFHR1 and CFHR3 genes. CFHR1, an abundant serum protein, is absent in subjects homozygous for the deletion. Genotyping analyses of AMD cases and controls from two cohorts demonstrates that deletion homozygotes comprise 1.1% of cases and 5.7% of the controls (chi-square=32.8; P= 1.6 E-09). CFHR1 and CFHR3 transcripts are abundant in liver, but undetectable in the ocular retinal pigmented epithelium/choroid complex. AMD-associated CFH/CFHR1/CFHR3 haplotypes are widespread in human populations. CONCLUSION: The absence of CFHR1 and/or CFHR3 may account for the protective effects conferred by some CFH haplotypes. Moreover, the high frequencies of the 402H allele and the delCFHR1/CFHR3 alleles in African populations suggest an ancient origin for these alleles. The considerable diversity accumulated at this locus may be due to selection, which is consistent with an important role for the CFHR genes in innate immunity.

Yzer S, Fishman GA, Racine J, Al-Zuhaibi S, Chakor H, Dorfman A, Szlyk J, Lachapelle P, van den Born LI, Allikmets R, Lopez I, Cremers FP, Koenekoop RK. · McGill Ocular Genetics Centre, Division of Ophthalmology, Montreal, Quebec, Canada. · Invest Ophthalmol Vis Sci. · Pubmed #16936081 links to  free full text

Abstract: PURPOSE: To test human CRB1 heterozygotes for possible clinical or functional retinal changes and to evaluate whether a patient with Leber congenital amaurosis (LCA) with CRB1 mutations not consistent with previously described CRB1 phenotypes carried a modifier allele in another LCA gene. METHODS: Seven unrelated heterozygous carriers of CRB1 mutations underwent phenotyping by full eye examinations (indirect ophthalmoscopy and slit lamp biomicroscopy) and functional testing (standard full-field electroretinography [ERG] and multifocal ERG). For genotyping of the LCA patients and their parents, denaturing high-performance liquid chromatography (dHPLC) analyses were performed, followed by sequence analysis of CRB1, followed by sequence analysis of the AIPL1 and CRX genes to identify a putative modifier effect in a patient with an atypical CRB1 phenotype. RESULTS: Reduced full-field ERG b-wave amplitudes were observed with scotopic -2 dB flash (140 microV; P < 0.05), normal full-field cone ERGs, and significant regional retinal dysfunction on mfERG in five of seven carriers of CRB1 mutations. A known AIPL1 mutation (p. R302L) was identified as a potential modifier allele in a patient with LCA carrying two CRB1 mutations and with a prominent maculopathy. CONCLUSIONS: In human heterozygotes of CRB1 mutations (parents of offspring with LCA), distinctive regional retinal dysfunctions were found by multifocal ERG measurements that were consistent with the focal histologic abnormalities reported for the two CRB1 knockout mice models. This phenotypic finding may identify CRB1 carriers and point to the causal gene defect in affected LCA offspring, significantly facilitating the molecular diagnostic process. Evidence suggests a modifier allele in AIPL1 in a patient with LCA with prominent atrophic macular lesions and homozygous defects in CRB1.

Gold B, Merriam JE, Zernant J, Hancox LS, Taiber AJ, Gehrs K, Cramer K, Neel J, Bergeron J, Barile GR, Smith RT, Anonymous00162, Hageman GS, Dean M, Allikmets R. · Laboratory of Genomic Diversity, National Cancer Institute, Frederick, Maryland 21702, USA. · Nat Genet. · Pubmed #16518403 No free full text.

Abstract: Age-related macular degeneration (AMD) is the most common form of irreversible blindness in developed countries. Variants in the factor H gene (CFH, also known as HF1), which encodes a major inhibitor of the alternative complement pathway, are associated with the risk for developing AMD. Here we test the hypothesis that variation in genes encoding other regulatory proteins of the same pathway is associated with AMD. We screened factor B (BF) and complement component 2 (C2) genes, located in the major histocompatibility complex class III region, for genetic variation in two independent cohorts comprising approximately 900 individuals with AMD and approximately 400 matched controls. Haplotype analyses identify a statistically significant common risk haplotype (H1) and two protective haplotypes. The L9H variant of BF and the E318D variant of C2 (H10), as well as a variant in intron 10 of C2 and the R32Q variant of BF (H7), confer a significantly reduced risk of AMD (odds ratio = 0.45 and 0.36, respectively). Combined analysis of the C2 and BF haplotypes and CFH variants shows that variation in the two loci can predict the clinical outcome in 74% of the affected individuals and 56% of the controls. These data expand and refine our understanding of the genetic risk for AMD.

Maiti P, Kong J, Kim SR, Sparrow JR, Allikmets R, Rando RR. · Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts 02115, USA. · Biochemistry. · Pubmed #16411761 No free full text.

Abstract: The accumulation of the lipofuscin fluorophores in retinal pigment epithelial (RPE) cells leads to the blinding degeneration characteristic of Stargardt disease and related forms of macular degeneration. RPE lipofuscin, including the fluorophore A2E, forms in large part as a byproduct of the visual cycle. Inhibiting visual cycle function with small molecules is required to prevent the formation of the retinotoxic lipofuscins. This in turn requires identification of rate-limiting steps in the operation of the visual cycle. Specific, non-retinoid isoprenoid compounds are described here, and shown through in both in vitro and in vivo experiments, to serve as antagonists of RPE65, a protein that is essential for the operation of the visual cycle. These RPE65 antagonists block regeneration of 11-cis-retinal, the chromophore of rhodopsin, thereby demonstrating that RPE65 is at least partly rate-limiting in the visual cycle. Furthermore, chronic treatment of a mouse model of Stargardt disease with the RPE65 antagonists abolishes the formation of A2E. Thus, RPE65 is also on the rate-limiting pathway to A2E formation. These nontoxic isoprenoid RPE65 antagonists are candidates for the treatment of forms of macular degeneration wherein lipofuscin accumulation is an important risk factor. These antagonists will also be used to probe the molecular function of RPE65 in vision.

Hargitai J, Zernant J, Somfai GM, Vamos R, Farkas A, Salacz G, Allikmets R. · 2nd Department of Ophthalmology, Semmelweis University, Budapest, Hungary. · Invest Ophthalmol Vis Sci. · Pubmed #16303926 links to  free full text

Abstract: PURPOSE: Autosomal recessive Stargardt disease (arSTGD) presents with substantial clinical and genetic heterogeneity. This study was conducted to correlate foveolar thickness (FT) and total macular volume (TMV), measured by optical coherence tomography (OCT), with other clinical characteristics and with specific genetic variation in Hungarian patients with arSTGD. METHODS: After a standard ophthalmic workup, both eyes of 35 patients with STGD from Hungary and of 25 age-matched healthy control subjects were tested with OCT. FT and TMV were measured automatically with the OCT mapping software in the nine Early Treatment Diabetic Retinopathy Study areas of 3500 microm in diameter. All patients were screened for mutations by a combination of the ABCR400 microarray and direct sequencing. RESULTS: The patients with STGD presented with markedly thinned retina in the foveola and decreased macular volume, 72 microm and 1.69 mm3, respectively, compared with 169 microm and 2.48 mm3 in the normal subjects, respectively. Statistically significant correlation was observed between visual acuity (VA) and TMV and between VA and FT. Disease-associated mutations were detected in 23 (65.7%) of 35 patients, including 48.5% with both alleles and 17.2% with one allele. The most frequent ABCA4 alleles in Hungarian patients with STGD were L541P/A1038V (in 28% of all patients), G1961E (20%) and IVS40+5G-->A (17%). Specific genotypes correlated with some phenotypic features and allowed for predictions of the disease progression. CONCLUSIONS: Hungarian patients with STGD presented with extensive foveolar thinning and macular volume loss. Genetic analysis detected several ABCA4 alleles at high frequency in the cohort of patients, suggesting founder effect(s). Unusually homogeneous distribution of disease-associated mutations aided genotype-phenotype correlation analyses in this population.

Simonelli F, Testa F, Zernant J, Nesti A, Rossi S, Allikmets R, Rinaldi E. · Department of Ophthalmology, Second University of Naples, Naples, Italy. · Ophthalmic Res. · Pubmed #15942264 No free full text.

Abstract: Autosomal recessive Stargardt disease (STGD) has been associated with substantial genetic and phenotypic heterogeneity. By systematic clinical analyses of STGD patients with complete genetic data (i.e. identified mutations on both alleles of the ABCA4 gene), we set out to determine phenotypic subtypes and to correlate these with specific ABCA4 alleles. Twenty-eight patients from 18 families with STGD/fundus flavimaculatus were investigated. All patients were submitted to complete ophthalmologic examination, electrophysiology, fluorescein angiography and ABCA4 gene chip analysis. Two main clinical phenotypes were observed among the examined patients. The severe phenotype was characterized by the onset of the disease <20 years and reduced ERG response, whereas the mild phenotype presented with later onset of the disease and a normal ERG response. Genetic analysis of the ABCA4 gene revealed, in the severe group, more frequently deletions, stop codons and insertions as compared to the mild phenotype group (p=0.0113 by Fisher's exact test). Moreover, the compound heterozygous mutations G1961E/5018+2T-->C found in 7 patients from 3 unrelated STGD families were associated with a mild phenotype in all subjects, except 1. This study documented variability of the clinical expression of STGD in relation to the age of onset of the disease, fundus appearance and the ERG response and allowed to subdivide patients into a severe and a mild phenotype group. These findings suggest that an extensive and comprehensive genetic analysis of STGD patients combined with thorough clinical evaluation, including the careful recording of the age of onset of the disease, would allow a more precise prognostic evaluation.

Fishkin NE, Sparrow JR, Allikmets R, Nakanishi K. · Department of Chemistry, Columbia University, New York, NY 10032, USA. · Proc Natl Acad Sci U S A. · Pubmed #15870200 links to  free full text

Abstract: Several lines of investigation suggest that the nondegradable fluorophores that accumulate as lipofuscin in retinal pigment epithelium (RPE) cells contribute to the etiology of macular degeneration. Despite evidence that much of this fluorescent material may originate as inadvertent products of the retinoid cycle, the enzymatic pathway by which the 11-cis-retinal chromophore of rhodopsin is generated, the only fluorophores of the RPE to be characterized as yet have been A2E and its isomers. Here, we report the isolation and structural characterization of an additional RPE lipofuscin fluorophore that originates as a condensation product of two molecules of all-trans-retinal (ATR) dimer and forms a protonated Schiff base conjugate with phosphatidylethanolamine (PE), the latter conjugate (ATR dimer-PE) having UV-visible absorbance maxima at 285 and 506 nm. ATR dimer was found to form natively in bleached rod outer segments in vitro and when rod outer segments were incubated with ATR. HPLC analysis of eye-cups that included RPE and isolated neural retina from Abcr-/- mice and RPE isolated from human donor eyes revealed the presence of a pigment with the same UV-visible absorbance and retention time as synthetic ATR dimer-PE conjugate. Evidence that ATR dimer undergoes a photooxidation process involving the addition of oxygens at double bonds as well as an aromatic demethylation also may indicate a role for this molecule, or its derivatives, in the photoreactivity of RPE lipofuscin.

Hageman GS, Anderson DH, Johnson LV, Hancox LS, Taiber AJ, Hardisty LI, Hageman JL, Stockman HA, Borchardt JD, Gehrs KM, Smith RJ, Silvestri G, Russell SR, Klaver CC, Barbazetto I, Chang S, Yannuzzi LA, Barile GR, Merriam JC, Smith RT, Olsh AK, Bergeron J, Zernant J, Merriam JE, Gold B, Dean M, Allikmets R. · Department of Ophthalmology and Visual Sciences, Cell Biology and Functional Genomics Laboratory, University of Iowa, Iowa City, IA 52240, USA. · Proc Natl Acad Sci U S A. · Pubmed #15870199 links to  free full text

Abstract: Age-related macular degeneration (AMD) is the most frequent cause of irreversible blindness in the elderly in developed countries. Our previous studies implicated activation of complement in the formation of drusen, the hallmark lesion of AMD. Here, we show that factor H (HF1), the major inhibitor of the alternative complement pathway, accumulates within drusen and is synthesized by the retinal pigmented epithelium. Because previous linkage analyses identified chromosome 1q25-32, which harbors the factor H gene (HF1/CFH), as an AMD susceptibility locus, we analyzed HF1 for genetic variation in two independent cohorts comprised of approximately 900 AMD cases and 400 matched controls. We found association of eight common HF1 SNPs with AMD; two common missense variants exhibit highly significant associations (I62V, chi2 = 26.1 and P = 3.2 x 10(-7) and Y402H, chi2 = 54.4 and P = 1.6 x 10(-13)). Haplotype analysis reveals that multiple HF1 variants confer elevated or reduced risk of AMD. One common at-risk haplotype is present at a frequency of 50% in AMD cases and 29% in controls [odds ratio (OR) = 2.46, 95% confidence interval (1.95-3.11)]. Homozygotes for this haplotype account for 24% of cases and 8% of controls [OR = 3.51, 95% confidence interval (2.13-5.78)]. Several protective haplotypes are also identified (OR = 0.44-0.55), further implicating HF1 function in the pathogenetic mechanisms underlying AMD. We propose that genetic variation in a regulator of the alternative complement pathway, when combined with a triggering event, such as infection, underlie a major proportion of AMD in the human population.

Umeda S, Ayyagari R, Allikmets R, Suzuki MT, Karoukis AJ, Ambasudhan R, Zernant J, Okamoto H, Ono F, Terao K, Mizota A, Yoshikawa Y, Tanaka Y, Iwata T. · National Institute of Sensory Organs, National Hospital Organization Tokyo Medical Center, Tokyo 152-8902, Japan. · Invest Ophthalmol Vis Sci. · Pubmed #15671300 links to  free full text

Abstract: PURPOSE: To describe hereditary macular degeneration observed in the cynomolgus monkey (Macaca fascicularis), which shares phenotypic features with age-related macular degeneration in humans, and to test the involvement of candidate gene loci by mutation screening and linkage analysis. METHODS: Ophthalmic examinations with fundus photography, fluorescein angiography (FA), indocyanine green angiography (IA), electroretinography (ERG), and histologic studies were performed on both affected and unaffected monkeys in the pedigree. The monkey orthologues of the human ABCA4, VMD2, EFEMP1, TIMP3, and ELOVL4 genes were cloned and screened for mutations by single-strand conformation polymorphism (SSCP) analysis or denaturing high-performance liquid chromatography (DHPLC) and direct sequencing in six affected and five unaffected monkeys from the pedigree and in six unrelated, unaffected monkeys. Subsequently, 13 human macular degeneration loci including these five genes were analyzed to test for linkage with the disease. Nineteen affected and seven unaffected monkeys in the pedigree were analyzed by using human microsatellite markers linked to the 13 loci. RESULTS: Yellowish white spots were observed in the macula and fovea centralis, and in some cases the spots scattered to the peripheral retina along the blood vessels. FA showed hyperfluorescence corresponding to the dots except in the foveola. No anomalies were found by IA and ERG. Histologic studies demonstrated that the spots were drusen. Mutation analysis of the ABCA4, VMD2, EFEMP1, TIMP3, and ELOVL4 genes identified a few sequence variants, but none of them segregated with the disease. Linkage analysis with markers linked to these five genes and an additional eight human macular degeneration loci failed to establish linkage. Haplotype analysis excluded the involvement of the 13 candidate loci for harboring the gene associated with macular degeneration in the monkeys. CONCLUSIONS: Significant homology was identified between monkey and human orthologues of the five macular degeneration genes. Thirteen loci associated with macular degeneration in humans or harboring macular degeneration genes were excluded as causal of early-onset macular degeneration in the monkeys. It is likely that none of these loci, but rather a novel gene, is involved in causing the observed phenotype in this monkey pedigree.

Hayashi M, Merriam JE, Klaver CC, Zernant J, Bergen AA, Smith RT, Chang S, Merriam JC, Allikmets R. · Department of Ophthalmology Columbia University Eye Institute Research, Rm. 715 630 West 168th Street New York, NY 10032 USA. · Ophthalmic Genet. · Pubmed #15370542 No free full text.

Abstract: The age-related maculopathy (ARM) genetics program at Columbia University utilizes comprehensive genetic analysis of candidate genes in large case-control studies to determine genotypes associated with the ARM complex trait. Genes encoding laminins, a class of extracellular matrix proteins, represent attractive candidates for two reasons. First, the presence of laminins in the basal lamina of the retinal pigment epithelium (RPE), Bruch's membrane, and choriocapillaris suggests a possible role in the pathophysiology of ARM. Second, three laminin genes, LAMC1, LAMC2, and LAMB3, are located in the 1q25-31 region, within the previously mapped ARMD1 locus. The entire open reading frame of the three laminin genes was screened for variants by denaturing high-performance liquid chromatography (DHPLC) and direct sequencing in at least 92, and up to 368 ARM patients and matched unaffected controls. Sixty-nine sequence variants were detected in the 69 exons of the LAMC1, LAMC2, and LAMB3 genes. Screening of exon 104 of the recently proposed ARMD1 gene, HEMICENTIN-1, residing in the 1q25-31 locus, did not detect the suggested causal variant, Q5345R, in 632 study subjects. Overall, we did not find statistically significant differences in the frequency of variants between ARM-affected individuals and age-matched controls. Four rare, non-synonymous, variants were detected in single cases of ARM patients. Our data on relatively limited numbers of study subjects do not suggest a significant role for genetic variation in the three laminin genes and in exon 104 of HEMICENTIN-1 in predisposing individuals to ARM. However, as in many instances in similar studies, involvement of rare amino acid-changing variants in a fraction of ARM cannot be ruled out.

Kim SR, Fishkin N, Kong J, Nakanishi K, Allikmets R, Sparrow JR. · Department of Ophthalmology, Columbia University, New York, NY 10027, USA. · Proc Natl Acad Sci U S A. · Pubmed #15277666 links to  free full text

Abstract: There is a growing body of evidence that the nondegradable fluorophores that accumulate as the lipofuscin of retinal pigment epithelium (RPE) are involved in mechanisms leading to the degeneration of RPE in macular degeneration. Most of the constituents of RPE lipofuscin are inadvertent products of the retinoid visual cycle, the enzymatic pathway by which the 11-cis-retinal chromophore of rhodopsin is generated. Indeed, a major constituent of RPE lipofuscin, the pyridinium bisretinoid A2E, is a diretinal conjugate that forms in photoreceptor cells and is deposited in RPE cells as a consequence of the phagocytosis of the outer segment membrane by RPE cells. Given the adverse effects of A2E, there is considerable interest in combating its deposition so as to protect against vision loss. These efforts, however, necessitate an understanding of factors that modulate its formation. Here we show that an amino acid variant in murine Rpe65, a visual-cycle protein required for the regeneration of 11-cis-retinal, is associated with reduced A2E accumulation.

Stenirri S, Fermo I, Battistella S, Galbiati S, Soriani N, Paroni R, Manitto MP, Martina E, Brancato R, Allikmets R, Ferrari M, Cremonesi L. · Unit of Genomics for Diagnosis of Human Pathologies, University Hospital San Raffaele, Milan, Italy. · Clin Chem. · Pubmed #15192030 links to  free full text

Abstract: BACKGROUND: Mutations in the retina-specific ABC transporter (ABCA4) gene have been associated with several forms of macular degenerations. Because the high complexity of the molecular genotype makes scanning of the ABCA4 gene cumbersome, we describe here the first use of denaturing HPLC (DHPLC) to screen for ABCA4 mutations. METHODS: Temperature conditions were designed for all 50 exons based on effective separation of 83 samples carrying 86 sequence variations and 19 mutagenized controls. For validation, samples from 23 previously characterized Stargardt patients were subjected to DHPLC profiling. Subsequently, samples from a cohort of 30 patients affected by various forms of macular degeneration were subjected to DHPLC scanning under the same conditions. RESULTS: DHPLC profiling not only identified all 132 sequence alterations previously detected by double-gradient denaturing gradient gel electrophoresis but also identified 5 sequence alterations that this approach had missed. Moreover, DHPLC scanning of an additional panel of 30 previously untested patients led to the identification of 26 different mutations and 29 polymorphisms, accounting for 203 sequence variations on 29 of the 30 patients screened. In total, the DHPLC approach allowed us to identify 16 mutations that had never been reported before. CONCLUSIONS: These results provide strong support for the use of DHPLC for molecular characterization of the ABCA4 gene.

Simonelli F, Testa F, Zernant J, Nesti A, Rossi S, Rinaldi E, Allikmets R. · Department of Ophthalmology, Second University of Naples, Naples, Italy. · Ophthalmic Res. · Pubmed #15017103 No free full text.

Abstract: Genetic variation in the ABCA4 (ABCR) gene has been associated with several distinct retinal phenotypes, including Stargardt disease/fundus flavimaculatus (STGD/FFM), cone-rod dystrophy (CRD), retinitis pigmentosa (RP) and age-related macular degeneration. The current model of genotype/phenotype association suggests that patients harboring deleterious mutations in both ABCR alleles would develop RP-like retinal pathology. Here we describe ABCA4-associated phenotypes, including a proband with a homozygous nonsense mutation in a family from Southern Italy. The proband had been originally diagnosed with STGD. Ophthalmologic examination included kinetic perimetry, electrophysiological studies and fluorescein angiography. DNA of the affected individual and family members was analyzed for variants in all 50 exons of the ABCA4 gene by screening on the ABCR400 microarray. A homozygous nonsense mutation 2971G>T (G991X) was detected in a patient initially diagnosed with STGD based on funduscopic evidence, including bull's eye depigmentation of the fovea and flecks at the posterior pole extending to the mid-peripheral retina. Since this novel nucleotide substitution results in a truncated, nonfunctional, ABCA4 protein, the patient was examined in-depth for the severity of the disease phenotype. Indeed, subsequent electrophysiological studies determined severely reduced cone amplitude as compared to the rod amplitude, suggesting the diagnosis of CRD. ABCR400 microarray is an efficient tool for determining causal genetic variation, including new mutations. A homozygous protein-truncating mutation in ABCA4 can cause a phenotype ranging from STGD to CRD as diagnosed at an early stage of the disease. Only a combination of comprehensive genotype/phenotype correlation studies will determine the proper diagnosis and prognosis of ABCA4-associated pathology.

Margalit E, Sunness JS, Green WR, Kelman SE, Schachat AP, Fiergang D, Allikmets R. · Wilmer Eye Institute, Baltimore, Maryland 21205, USA. · Arch Ophthalmol. · Pubmed #14609928 No free full text.

This publication has no abstract.

Jaakson K, Zernant J, Külm M, Hutchinson A, Tonisson N, Glavac D, Ravnik-Glavac M, Hawlina M, Meltzer MR, Caruso RC, Testa F, Maugeri A, Hoyng CB, Gouras P, Simonelli F, Lewis RA, Lupski JR, Cremers FP, Allikmets R. · Asper Biotech, Tartu, Estonia. · Hum Mutat. · Pubmed #14517951 No free full text.

Abstract: Genetic variation in the ABCR (ABCA4) gene has been associated with five distinct retinal phenotypes, including Stargardt disease/fundus flavimaculatus (STGD/FFM), cone-rod dystrophy (CRD), and age-related macular degeneration (AMD). Comparative genetic analyses of ABCR variation and diagnostics have been complicated by substantial allelic heterogeneity and by differences in screening methods. To overcome these limitations, we designed a genotyping microarray (gene chip) for ABCR that includes all approximately 400 disease-associated and other variants currently described, enabling simultaneous detection of all known ABCR variants. The ABCR genotyping microarray (the ABCR400 chip) was constructed by the arrayed primer extension (APEX) technology. Each sequence change in ABCR was included on the chip by synthesis and application of sequence-specific oligonucleotides. We validated the chip by screening 136 confirmed STGD patients and 96 healthy controls, each of whom we had analyzed previously by single strand conformation polymorphism (SSCP) technology and/or heteroduplex analysis. The microarray was >98% effective in determining the existing genetic variation and was comparable to direct sequencing in that it yielded many sequence changes undetected by SSCP. In STGD patient cohorts, the efficiency of the array to detect disease-associated alleles was between 54% and 78%, depending on the ethnic composition and degree of clinical and molecular characterization of a cohort. In addition, chip analysis suggested a high carrier frequency (up to 1:10) of ABCR variants in the general population. The ABCR genotyping microarray is a robust, cost-effective, and comprehensive screening tool for variation in one gene in which mutations are responsible for a substantial fraction of retinal disease. The ABCR chip is a prototype for the next generation of screening and diagnostic tools in ophthalmic genetics, bridging clinical and scientific research.

Seddon JM, Sharma S, Chong S, Hutchinson A, Allikmets R, Adelman RA. · Department of Ophthalmology, Massachusetts Eye and Ear Infirmary, Harvard Medical School, Boston, Massachusetts 02114, USA. · Ophthalmology. · Pubmed #13129869 No free full text.

Abstract: OBJECTIVE: To evaluate mutations in the Best mascular dystrophy (VMD2) gene in two families with Best disease and to describe the phenotype-genotype correlations of genetically determined affected and unaffected individuals. DESIGN: Family genetic study. PARTICIPANTS: Two families with Best disease were identified, and family members were evaluated by ophthalmologic examination or fundus photography to assess their phenotype. All affected patients and some of the unaffected family members had a blood sample drawn, and the DNA was analyzed for mutations in the VMD2 gene. MAIN OUTCOME MEASURES: Twenty-one subjects in the two pedigrees with Best disease were studied. One amino acid-changing mutation in the VMD2 gene was found to segregate independently in each family (P297S or E300D, respectively). RESULTS: Eleven individuals had some evidence of maculopathy, including retinal pigment epithelial changes, drusen, pigment epithelial irregularities, or cicatricial changes. Ten of these 11 patients (91%) with maculopathy had a mutation in the VMD2 gene, of whom 8 were clinically diagnosed as having Best disease and 2 were diagnosed as having possible Best maculopathy. The one patient without a mutation in the VMD2 gene had age-related macular degeneration (AMD). Ten family members did not have evidence of maculopathy, of whom 6 had no mutation in the VMD2 gene. Four family members (2 in each pedigree) had mutations in the VMD2 gene, abnormal electro-oculogram (EOG) results, but normal maculae at age 40 or older. Of the 7 individuals with no mutation in the VMD2 gene, 6 were phenotypically normal and the other had late-onset visual loss resulting from AMD. CONCLUSIONS: All family members with maculopathy consistent with Best disease (n = 10) had an amino acid-changing mutation in the VMD2 gene. Four individuals who did not have maculopathy, but did have an abnormal EOG, also had mutations in the VMD2 gene. The presence of a VMD2 mutation is associated with abnormal retinal function, which can occur in the absence of phenotypic manifestation of macular disease.