Macular Degeneration: Koenekoop RK

Koenekoop RK. · Department of Ophthalmology, McGill University, Montreal Children's Hospital, 2300 Tupper, Montreal, Quebec H3H 1P3, Canada. · Ophthalmic Genet. · Pubmed #12789571 No free full text.

Abstract: The gene ABCA4 encodes the rod and cone photoreceptor Rim protein, which is a transmembrane transporter of vitamin A intermediates. ABCA 4 mutations are responsible for a large variety of retinal degenerations including all cases of Stargardt macular dystrophy and fundus flavimaculatus, some forms of cone-rod degeneration, and retinitis pigmentosa, and likely increase the risk of developing age-related macular degeneration (AMD). The purpose of this mini-review is to highlight the advances in our understanding of Stargardt disease and the ABCA4 gene from the first description of the disease by Karl Stargardt in 1909 to gene discovery by Allikmets and colleagues in 1997. The knockout mouse model by Mata and co-workers has provided crucial pathophysiological information that has led to new ideas regarding treatment possibilities. These hypotheses were tested by Radu and colleagues in the mouse and shown to be efficacious.

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.

Dharmaraj S, Leroy BP, Sohocki MM, Koenekoop RK, Perrault I, Anwar K, Khaliq S, Devi RS, Birch DG, De Pool E, Izquierdo N, Van Maldergem L, Ismail M, Payne AM, Holder GE, Bhattacharya SS, Bird AC, Kaplan J, Maumenee IH. · Johns Hopkins Center for Hereditary Eye Diseases, Wilmer Eye Institute, Johns Hopkins Medical Institutions, Baltimore, MD 21287-9237, USA. · Arch Ophthalmol. · Pubmed #15249368 links to  free full text

Abstract: OBJECTIVES: To describe the phenotype of Leber congenital amaurosis (LCA) in 26 probands with mutations in aryl hydrocarbon receptor interacting protein-like 1 protein (AIPL1) and compare it with phenotypes of other LCA-related genes. To describe the electroretinogram (ERG) in heterozygote carriers. METHODS: Patients with AIPL1-related LCA were identified in a cohort of 303 patients with LCA by polymerase chain reaction single-strand confirmational polymorphism mutation screening and/or direct sequencing. Phenotypic characterization included clinical and ERG evaluation. Seven heterozygous carrier parents also underwent ERG testing. RESULTS: Seventeen homozygotes and 9 compound heterozygotes were identified. The W278X mutation was most frequent (48% of alleles). Visual acuities ranged from light perception to 20/400. Variable retinal appearances, ranging from near normal to varying degrees of chorioretinal atrophy and intraretinal pigment migration, were noted. Atrophic and/or pigmentary macular changes were present in 16 (80%) of 20 probands. Keratoconus and cataracts were identified in 5 (26%) of 19 patients, all of whom were homozygotes. The ERG of a parent heterozygote carrier revealed significantly reduced rod function, while ERGs for 6 other carrier parents were normal. CONCLUSIONS: The phenotype of LCA in patients with AIPL1 mutations is relatively severe, with a maculopathy in most patients and keratoconus and cataract in a large subset. Rod ERG abnormalities may be present in heterozygous carriers of AIPL1 mutations. CLINICAL RELEVANCE: Understanding and recognizing the phenotype of LCA may help in defining the course and severity of the disease. Identifying the gene defect is the first step in preparation for therapy since molecular diagnosis in LCA will mandate the choice of treatment.

Heckler LV, Lederer DE, Alwadani F, Koenekoop RK. · No affiliation provided · Can J Ophthalmol. · Pubmed #18443618 links to  free full text

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