A comprehensive clinical and biochemical functional study of a novel RPE65 hypomorphic mutation

PURPOSE. Later onset and progression of retinal dystrophy occur with some RPE65 missense mutations. The functional consequences of the novel P25L RPE65 mutation was correlated with its early-childhood phenotype and compared with other pathogenic missense mutations. METHODS. In addition to typical clinical tests, fundus autofluorescence (FAF), optical coherence tomography (OCT), and two-color threshold perimetry (2CTP) were measured. RPE65 mutations were screened by SSCP and direct sequencing. Isomerase activity of mutant RPE65 was assayed in 293F cells and quantified by HPLC analysis of retinoids. RESULTS. A very mild phenotype was detected in a now 7-yearold boy homozygous for the P25L mutation in RPE65. Although abnormal dark adaptation was noticed early, best corrected visual acuity was 20/20 at age 5 years and 20/30 at age 7 years. Nystagmus was absent. Cone electroretinogram (ERG) was measurable, rod ERG severely reduced, and FAF very low. 2CTP detected mainly cone-mediated responses in scotopic conditions, and light-adapted cone responses were approximately 1.5 log units below normal. High-resolution spectral domain OCT revealed morphologic changes. Isomerase activity in 293F cells transfected with RPE65/P25L was reduced to 7.7% of wild-type RPE65-transfected cells, whereas RPE65/ L22P-transfected cells had 13.5%. CONCLUSIONS. The mild clinical phenotype observed is consistent with the residual activity of a severely hypomorphic mutant RPE65. Reduction to Ͻ10% of wild-type RPE65 activity by homozygous P25L correlates with almost complete rod function loss and cone amplitude reduction. Functional survival of cones is possible in patients with residual RPE65 isomerase activity. This patient should profit most from gene therapy. (Invest Ophthalmol Vis Sci. 2008;49:5235-5242) DOI: 10.1167/iovs.07-1671 H uman mutations in the gene for the highly preferentially expressed RPE protein RPE65 are associated with a spectrum of retinal dystrophies ranging from more severe earlyonset conditions, variously described as Leber congenital amaurosis type 2/autosomal recessive childhood-onset severe retinal dystrophy or early-onset severe retinal dystrophy (LCA2/arCSR, EOSRD) to later onset conditions described as autosomal recessive retinitis pigmentosa (arRP). 1-7 Recently, RPE65 has been established as the isomerase central to the retinoid visual cycle. 8 -10 This cycle 11 is crucial for supply of the chromophore 11-cis retinal for visual pigment regeneration. Animal models have contributed greatly to our understanding of the role of RPE65 in the visual cycle, regeneration, and retinal dystrophy. Rpe65 knockout mice display a biochemical phenotype consisting of extreme chromophore starvation (no rhodopsin) in the photoreceptors concurrent with overaccumulation of all-trans retinyl esters in the RPE 10 and are extremely insensitive to light. This insensitivity to light protects Rpe65 Ϫ/Ϫ mice from light damage, establishing rhodopsin as the mediator of light-induced retinal damage. 12 There is also a natural mutation in mouse Rpe65 called rd12. 14,15 The utility of gene therapy was established by preclinical trials in these dogs. 21 This level appears to be more than enough to maintain near-normal function. In contrast, human RPE65 EOSRD displays a wide spectrum of severity, age of onset, and progression not seen in animal models. In this article, we present the mild phenotypic consequences of a homozygous P25L missense mutation in a young patient and correlate these with the biochemical effect of this mutation on RPE65 activity. We show that even though the isomerase activity of the mutant RPE65 was quite impaired, the patient had near-normal visual acuity. However, rod function was extremely impaired. In addition, short-wavelength cones appeared more impaired than long-wavelength cones, consistent with findings in other patients with RPE65 mutations that blue color vision is much more and earlier impaired than is red vision, opposite to the usual case in cone dystrophies. These From th

Clinical characterization of 66 patients with congenital retinal disease due to the deep-intronic c.2991+1655A>G mutation in CEP290

PURPOSE. To describe the phenotypic spectrum of retinal disease caused by the c.2991+1655A>G mutation in CEP290 and to compare disease severity between homozygous and compound heterozygous patients. METHODS. Medical records were reviewed for best-corrected visual acuity (BCVA), age of onset, fundoscopy descriptions. Foveal outer nuclear layer (ONL) and ellipsoid zone (EZ) presence was assessed using spectral-domain optical coherence tomography (SD-OCT). Differences between compound heterozygous and homozygous patients were analyzed based on visual performance and visual development. RESULTS. A total of 66 patients were included. The majority of patients had either light perception or no light perception. In the remaining group of 14 patients, median BCVA was 20/195 Snellen (0.99 LogMAR; range 0.12–1.90) for the right eye, and 20/148 Snellen (0.87 LogMAR; range 0.22–1.90) for the left. Homozygous patients tended to be more likely to develop light perception compared to more severely affected compound heterozygous patients (P = 0.080) and are more likely to improve from no light perception to light perception (P = 0.022) before the age of 6 years. OCT data were available in 12 patients, 11 of whom had retained foveal ONL and EZ integrity up to 48 years (median 23 years) of age. CONCLUSIONS. Homozygous patients seem less severely affected compared to their compound-heterozygous peers. Improvement of visual function may occur in the early years of life, suggesting a time window for therapeutic intervention up to the approximate age of 17 years. This period may be extended by an intact foveal ONL and EZ on OCT

Mutations in RD3

PURPOSE. To identify the underlying mutation and describe the phenotype in a consanguineous Kurdish family with Leber's congenital amaurosis (LCA)/early onset severe retinal dystrophy (EOSRD). METHODS. Members of the index family were followed up to 22 years by ophthalmological examinations, including best corrected visual acuity (BCVA), Goldmann visual field (GVF), two-color-threshold perimetry (2CTP) and Ganzfeld electroretinogram (ERG), fundus photographs, fundus autofluorescence (FAF), and optical coherence tomography (OCT). After excluding seven of nine known LCA/EOSRD genes in the index patient, linkage analysis was performed in the family using a microarray followed by microsatellite fine mapping and direct sequencing of candidate genes. RD3 was screened by direct sequencing of 85 independent patients with LCA/EOSRD presenting with a BCVA ≥ 1.0 LogMAR before the age of 2 years to assess the prevalence of RD3 mutations in LCA/EOSRD. Since RD3 and RetGC1 have a functional relation, study authors screened for a modifying effect of RD3 mutations in 17 independent patients with mutations in GUCY2D. RESULTS. BCVA was severely reduced from the earliest examinations (as early as 3 months), never exceeding 1.3 LogMAR. The disease presented as cone-rod dystrophy with dystrophic changes in the macula and bone spicules in the periphery on progression. Linkage analysis narrowed the region of interest towards the LCA12 locus. Direct sequencing of RD3 revealed a homozygous nonsense mutation (c.180C > A) in all affected members tested. Screening of additional unrelated LCA/EOSRD patients revealed only polymorphisms in RD3. CONCLUSIONS. This is the second family reported so far with mutations in RD3. Mutations in RD3 are a very rare cause of LCA associated with an extremely severe form of retinal dystrophy

Bestrophin 1 – Phenotypes and Functional Aspects in Bestrophinopathies

<div><p></p><p>This is to review the current state of knowledge on the functional and clinical aspects of bestrophin 1, a prominent member of a family of proteins involved in the control and properties of the light peak of the EOG. Initially human bestrophin 1 gene (<i>BEST1</i>) mutations were identified to underlie Best vitelliform macular dystrophy (VMD), a dominantly inherited, juvenile-onset form of macular degeneration. In the recent past the phenotypical spectrum of retinal disorders associated with <i>BEST1</i> mutations has been extended and the term bestrophinopathies was coined. The physiological role of bestrophin 1 is still not completely understood but has been linked to the generation of a transepithelial chloride current by controlling voltage-dependent calcium channels (VDCC). Dysfunction of bestrophin 1 may result in abnormal ion and fluid transport by the retinal pigment epithelium (RPE) disturbing and even disrupting direct interactions between the RPE and the photoreceptors.</p></div