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Daiki Kubota, Kaori Matsumoto, Mika Hayashi, Noriko Oishi, Kiyoko Gocho, Kunihiko Yamaki, Shinichiro Kobayakawa, Tsutomu Igarashi, Hiroshi Takahashi, Shuhei Kameya | Ophthalmic Genetics | 20 Aug 2020 | 41 (6) | pgs. 629–638 | doi.org/10.1080/13816810.2020.1810284 Abstract Purpose The hexokinase 1 ( HK1 ) gene encodes one of the four human hexokinases that play essential roles in glucose metabolism. Recently, several cases of E847K mutation in the HK1 gene were reported to cause inherited retinal dystrophy. The purpose of this study was to identify the phenotypical characteristics of patients with a recurrent E847K mutation in the HK1 gene. Methods Three generations of one family with autosomal dominant retinitis pigmentosa were examined. Whole exome sequencing was performed on the DNA. Fundus imaging by an adaptive optics fundus camera was used to obtain high-resolution photoreceptor images. Results Fundus examination of the proband showed degeneration of the mid-peripheral retina, and SD-OCT images showed an absence of the ellipsoid zone (EZ) and interdigitation zone (IZ) in the parafovea and more peripherally. SD-OCT images of the mother of the proband showed an absence of the EZ and IZ, and fundus autofluorescence images showed hypo-autofluorescence surrounding the macular region. One daughter of the proband had only mild night blindness, however, the density of the cone photoreceptors was reduced in the parafoveal region. Whole exome sequencing identified a heterozygous variant, E847K, in the HK1 gene. This variant was found to co-segregate with the disease in three family members. Conclusions Although the systemic phenotypes were found to be associated with the HK1 mutations, only the E847K mutation can cause a non-syndromic photoreceptor degeneration. Our study strengthened the hypothesis that the amino acid E847 might play a critical role in the maintenance of the morphology and function of the photoreceptors. Introduction The hexokinase 1 ( HK1 ; OMIM 14260) gene encodes one of the four human hexokinases that play essential roles in glucose metabolism ( Citation1–3 ). Hexokinase catalyzes the first step in glucose metabolism using ATP for the phosphorylation of glucose to glucose-6-phosphate. Four different forms of hexokinase, HK1, HK2, HK3, and HK4 that are encoded by different genes, are present in mammalian tissues ( Citation3 ). Among these, HK1 is the most ubiquitously expressed and is the predominant hexokinase in the brain, erythrocytes, lymphocytes, and fibroblasts ( Citation1 ). A proteomic study of rats found that HK1 and HK2 are expressed in the retina ( Citation4 ). HK1 was found to be strongly expressed in the photoreceptor inner segment and in the outer plexiform layer, inner nuclear layer, inner plexiform layer, and ganglion cell layer ( Citation4 ). Thus far, four phenotypes that are associated with HK1 mutations have been listed in the OMIM database ( Citation5 ). They are nonspherocytic hemolytic anemia (NSHA) due to hexokinase deficiency (OMIM; 235700), Russe type of hereditary motor and sensory neuropathy (HMSNR, OMIM; 605285), retinitis pigmentosa 79 (RP79, OMIM; 617460), and neurodevelopmental disorder with visual defects and brain anomalies (NEDVIBA, OMIM; 618547). NSHA, due to hexokinase deficiency, and the Russe type of HMSNR are autosomal recessive inheritance disorders that are caused by homozygous or compound heterozygous loss-of function mutations of the HK1 gene ( Citation6–8 ). On the other hand, five families of autosomal dominant retinitis pigmentosa (adRP; RP79) were reported by Sullivan et al. who reported on a heterozygous missense Glu847Lys (E847K) mutation in the HK1 gene that segregated fully with the disease in each family ( Citation9 ). None of the patients had any extraocular manifestations, and none had any systemic abnormalities in glycolysis ( Citation9 ). Later, several groups reported similar non-syndromic autosomal dominant retinitis pigmentosa or allied diseases with the same heterozygous E847K mutation in the HK1 gene ( Citation10–13 ). Most recently, seven patients from six unrelated families with NEDVIBA were reported by Okur et al. They identified four different de novo heterozygous missense mutations in the HK1 gene in these patients ( Citation14 ). They also reported that these patients were syndromic, and several cases had a combination of retinitis pigmentosa and optic atrophy. However, the inheritance pattern and detailed ophthalmic findings were uncertain because a pedigree analysis and fundus images were not presented ( Citation14 ). The purpose of this study was to determine the phenotypic characteristics of the members of a Japanese family with a recurrent E847K mutation in the HK1 gene. To accomplish this, the family members underwent comprehensive ocular examinations including high-resolution retinal imaging by an adaptive optics fundus camera. Click here to read entire article References Katzen HM, Schimke RT. Multiple forms of hexokinase in the rat: tissue distribution, age dependency, and properties. Proc Natl Acad Sci U S A. 1965 Oct;54(4):1218–25. PMID: 5219826; PMCID: PMC219842. doi:10.1073/pnas.54.4.1218. Aleshin AE, Zeng C, Bourenkov GP, Bartunik HD, Fromm HJ, Honzatko RB. The mechanism of regulation of hexokinase: new insights from the crystal structure of recombinant human brain hexokinase complexed with glucose and glucose-6-phosphate. 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Nanda Boon, Jan Wijnholds, and Lucie P. Pellissier |  Frontier Neuroscience |  Vol 14 | 2020 Aug 14 |  doi.org/10.3389/fnins.2020.00860 Retinitis pigmentosa (RP) and Leber congenital amaurosis (LCA) are inherited degenerative retinal dystrophies with vision loss that ultimately lead to blindness. Several genes have been shown to be involved in early onset retinal dystrophies, including CRB1 and RPE65 . Gene therapy recently became available for young RP patients with variations in the RPE65 gene. Current research programs test adeno-associated viral gene augmentation or editing therapy vectors on various disease models mimicking the disease in patients. These include several animal and emerging human-derived models, such as human-induced pluripotent stem cell (hiPSC)-derived retinal organoids or hiPSC-derived retinal pigment epithelium (RPE), and human donor retinal explants. Variations in the CRB1 gene are a major cause for early onset autosomal recessive RP with patients suffering from visual impairment before their adolescence and for LCA with newborns experiencing severe visual impairment within the first months of life. These patients cannot benefit yet from an available gene therapy treatment. In this review, we will discuss the recent advances, advantages and disadvantages of different CRB1 human and animal retinal degeneration models. In addition, we will describe novel therapeutic tools that have been developed, which could potentially be used for retinal gene augmentation therapy for RP patients with variations in the CRB1 gene. CRB Family Members Crumbs (Crb) is a large transmembrane protein initially discovered at the apical membrane of Drosophila epithelial cells ( Tepass et al., 1990 ). Several years later, it was found that mutations in a human homolog of the Drosophila melanogaster protein crumbs, denoted as CRB1 (Crumbs homolog 1), was involved in retinal dystrophies in humans ( Den Hollander et al., 1999 ). The human CRB1 gene is mapped to chromosome 1q31.3, and contains 12 exons, has 12 identified transcript variants so far, three CRB family members, and over 210 kb genomic DNA ( Den Hollander et al., 1999 ) 1 . Canonical CRB1 is, like its Drosophila homolog, a large transmembrane protein consisting of multiple epidermal growth factor (EGF) and laminin-globular like domains in its extracellular N-terminus ( Figure 1A ). The intracellular C-terminal domain contains a FERM and a conserved glutamic acid-arginine-leucine-isoleucine (ERLI) PDZ binding motives. An alternative transcript of CRB1, CRB1-B , was recently described and suggested to have significant extracellular domain overlap with canonical CRB1 while bearing unique 5′ and 3′ domains ( Ray et al., 2020 ). In mammals, CRB1 is a member of the Crumbs family together with CRB2 and CRB3 ( Figure 1A ). CRB2 displays almost the same protein structure as CRB1, except a depletion of four EGF domains. CRB3A lacks the entire typical extracellular domain but contains the transmembrane domain juxtaposed to the intracellular part with the FERM-binding motif and a ERLI PDZ sequence. A second protein (isoform CRB3B) arises from the same CRB3 gene due to alternate splicing of the last exon, resulting in a different C-terminus with a cysteine-leucine-proline-isoleucine (CLPI) amino acid sequence, and thus lacks the PDZ domain ( Fan et al., 2007 ; Margolis, 2018 ). Interestingly, the CRB3B isoform is found in mammals, but not in zebrafish or Drosophila ( Fan et al., 2007 ). Further details about CRB isoform details can be found in Quinn et al. (2017) . References Adachi, M., Hamazaki, Y., Kobayashi, Y., Itoh, M., Tsukita, S., Furuse, M., et al. (2009). 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Aug 12, 2020 | David Hutton The FDA this week granted the fourth Orphan Drug Designation (ODD) for a novel gene therapy product candidate (OCU400, Ocugen Inc.) in the treatment of PDE6B gene mutation-associated retinal diseases. This designation targets retinitis pigmentosa (RP) caused by PDE6B mutations. RP that is a result of this mutation leads to blindness by midlife, and is characterized by the progressive loss of photoreceptors — with or without the loss of retinal pigment epithelium cells. At least one mutation in the PDE6B gene has been found to cause autosomal dominant congenital stationary night blindness, which is characterized by the inability to see in low light. According to a press release, Ocugen’s modifier gene therapy platform allows ophthalmologists to address multiple diseases with a single product. The novel gene therapy product candidate has the potential to be broadly effective in restoring retinal integrity and function across a range of genetically diverse inherited retinal diseases. It consists of a functional copy of a nuclear hormone receptor (NHR) gene, NR2E3, delivered to target cells in the retina using an adeno-associated viral vector. As a potent modifier gene, expression of NR2E3 within the retina may help reset retinal homeostasis and potentially offer longer benefit, stabilizing cells and rescuing photoreceptor degeneration and vision loss. Click here to read the source article.

Sriganesh Ramachandra Rao, Lara A. Skelton, Fuguo Wu, Agnieszka Onysk, Grzegorz Spolnik, Witold Danikiewicz, Mark C. Butler, Delores A. Stacks, Liliana Surmacz, Xiuqian Mu, Ewa Swiezewska, Steven J. Pittler, Steven J. Fliesler | iScience | Vol 23, Issue 6 | June 2020 26 |  doi.org/10.1016/j.isci.2020.101198 Summary Dehydrodolichyl diphosphate synthase (DHDDS) catalyzes the committed step in dolichol synthesis. Recessive mutations in DHDDS cause retinitis pigmentosa (RP59), resulting in blindness. We hypothesized that rod photoreceptor-specific ablation of Dhdds would cause retinal degeneration due to diminished dolichol-dependent protein N -glycosylation. Dhdds flx/flx mice were crossed with rod-specific Cre recombinase-expressing (Rho-iCre75) mice to generate rod-specific Dhdds knockout mice ( Dhdds flx/flx iCre+). In vivo morphological and electrophysiological evaluation of Dhdds flx/flx iCre+ retinas revealed mild retinal dysfunction at postnatal (PN) 4 weeks, compared with age-matched controls; however, rapid photoreceptor degeneration ensued, resulting in almost complete loss of rods and cones by PN 6 weeks. Retina dolichol levels were markedly decreased by PN 4 weeks in Dhdds flx/flx iCre+ mice, relative to controls; despite this, N -glycosylation of retinal proteins , including opsin (the dominant rod-specific glycoprotein), persisted in Dhdds flx/flx iCre+ mice. These findings challenge the conventional mechanistic view of RP59 as a congenital disorder of glycosylation . Introduction Retinitis pigmentosa (RP) represents a large class of inherited retinal dystrophies caused by mutations in several families of genes, leading to pigmentary retinopathy and progressive, irreversible blindness. Typically, RP is characterized by the initial loss of rod photoreceptors (PRs), deposition of pigment granules, and peripheral vision loss ( Ferrari et al., 2011 , Hamel, 2006 ). Defective asparagine-linked glycosylation ( N -glycosylation) of proteins in rod cells, particularly the visual pigment rhodopsin (RHO), results in progressive, irreversible rod cell degeneration and death, with concomitant loss of vision ( Murray et al., 2009 , Murray et al., 2015 , Kaushal et al., 1994 , Fliesler et al., 1984a ). Successful glycosylation of RHO is necessary for its vectorial trafficking through the inner segment (cell body) of the rod cell to the site of rod outer segment (ROS) membrane assembly at the base of the ROS. Retinal degeneration has been observed in patients harboring RHO mutations involving the N -glycosylation consensus sites, and in animal models involving comparable RHO mutations ( Van Den Born et al., 1994 , Zhu et al., 2004 , Sullivan et al., 1993 , Murray et al., 2015 , Iwabe et al., 2016 ), as well as by tunicamycin-induced and genetic inhibition of global/RHO N -glycosylation ( Fliesler and Basinger, 1985 , Fliesler et al., 1985 , Sabry et al., 2016 , Thompson et al., 2013 , Murray et al., 2015 ). Protein N -glycosylation involves the following steps (schematic representation, Figure 1 ): generation of dolichol (Dol, an important isoprenoid arising from the mevalonate pathway) and dolichyl phosphate (Dol-P, the obligate glycan carrier necessary for N -linked glycosylation, O -mannosylation, and C -mannosylation) ( Burda and Aebi, 1999 , Endo et al., 2003 , Park et al., 2014 , Cantagrel et al., 2010 , Burton et al., 1979 , Maeda et al., 2000 , Doucey et al., 1998 ), generation of complex Dol-P-linked oligosaccharides (DLO) ( Krasnova and Wong, 2016 , Gandini et al., 2017 , Behrens and Leloir, 1970 ), and transfer of those oligosaccharides from DLO to the N -glycosylation consensus site on the target polypeptide ( Welply et al., 1983 ). Genetic defects affecting the glycosylation mechanism constitute a large family of syndromes termed “congenital disorders of glycosylation” (CDGs), with more than 150 causative genes ( Ng and Freeze, 2018 , Sparks and Krasnewich, 1993 ). A family of genetic diseases pertaining to Dol synthesis is classified as CDG-I (the class of CDG involving defective glycan assembly and/or their transfer in the endoplasmic reticulum [ER]) due to the requirement of DLO for N -glycosylation. Common clinical features of CDGs include failure to thrive, retarded development, protein-losing enteropathy, early-onset encephalopathy, as well as retinopathies such as RP ( Sparks and Krasnewich, 1993 , Thompson et al., 2013 , Hamdan et al., 2017 , Morava et al., 2009 ).

A new gene therapy has been used to treat patients with a rare inherited eye disorder which causes blindness. It's hoped the NHS treatment will halt sight loss and even improve vision. Matthew Wood, 48, one of the first patients to receive the injection, told the BBC: "I value the remaining sight I have so if I can hold on to that it would be a big thing for me." The treatment costs around £600,000 but NHS England has agreed a discounted price with the manufacturer Novartis. Luxturna (voretigene neparvovec), has been approved by The National Institute for Health and Care Excellence (NICE), which estimates that just under 90 people in England will be eligible for the treatment. The gene therapy is for patients who have retinal dystrophy as a result of inheriting a faulty copy of the RPE65 gene from both parents. The gene is important for providing the pigment that light sensitive cells need to absorb light. Initially this affects night vision but eventually, as the cells die, it can lead to complete blindness. Read more . . .

By Patricia C Sanchez Diaz, DVM, PhD, FAAO Purpose This report aims to illustrate the impact of genetic testing in the diagnosis and management of hereditary retinal dystrophy. Here we describe the genetic changes identified in the USH2A gene in three patients with a clinical diagnosis of Usher syndrome (RP plus hearing loss) and discuss the implications of these genetic findings in helping patients to better understand their condition and to plan for their future. Read more

Changyi Ji , Yao Li , Alec Kittredge , Austin Hopiavuori , Nancy Ward , Peng Yao , Yohta Fukuda , Yu Zhang , Stephen H. Tsang , Tingting Yang  | Scientific Reports | Vol 9 | 19026 | 13 Dec 2019 | https://doi.org/10.1038/s41598-019-54892-7 Abstract BEST1 is a Ca2+-activated Cl− channel predominantly expressed in retinal pigment epithelium (RPE), and over 250 genetic mutations in the BEST1 gene have been identified to cause retinal degenerative disorders generally known as bestrophinopathies. As most BEST1 mutations are autosomal dominant, it is of great biomedical interest to determine their disease-causing mechanisms and the therapeutic potential of gene therapy. Here, we characterized six Best vitelliform macular dystrophy (BVMD)-associated BEST1 dominant mutations by documenting the patients’ phenotypes, examining the subcellular localization of endogenous BEST1 and surface Ca2+-dependent Cl− currents in patient-derived RPEs, and analyzing the functional influences of these mutations on BEST1 in HEK293 cells. We found that all six mutations are loss-of-function with different levels and types of deficiencies, and further demonstrated the restoration of Ca2+-dependent Cl− currents in patient-derived RPE cells by WT BEST1 gene supplementation. Importantly, BEST1 dominant and recessive mutations are both rescuable at a similar efficacy by gene augmentation via adeno-associated virus (AAV), providing a proof-of-concept for curing the vast majority of bestrophinopathies. Introduction Genetic mutation of the human BEST1 gene causes bestrophinopathies, which consist of a spectrum of retinal degeneration disorders including Best vitelliform macular dystrophy (BVMD) 1 , 2 , autosomal recessive bestrophinopathy (ARB) 3 , adult-onset vitelliform dystrophy (AVMD) 4 , 5 , autosomal dominant vitreoretinochoroidopathy (ADVIRC) 6 , and retinitis pigmentosa (RP) 7 . BVMD, featuring an early-onset and debilitating form of central macular degeneration, is the most common bestrophinopathy. Due to abnormalities in the fluid and/or electrolyte homeostasis between the RPE and photoreceptor outer segments 8 , the disease leads to the formation of serous retinal detachment and lesions that resemble egg yolk, or vitelliform, while rod and cone photoreceptor function remains unaffected. All types of bestrophinopathies, except for ARB, result from autosomal dominant mutation of BEST1 . Patients are susceptible to untreatable, progressive vision loss, which significantly deteriorates life quality. Therefore, understanding the mechanisms of BEST1 disease-causing mutations and designing strategies to restore the damaged cellular function are critical for developing treatments for bestrophinopathies. The protein encoded by the BEST1 gene is a Cl− channel named BESTROPHIN1 (BEST1), which is activated in response to intracellular Ca2+ and conducts Ca2+-dependent Cl− current on the cell membrane of retinal pigment epithelium (RPE) 1 , 2 , 9 , 10 . Consistently, Ca2+-dependent Cl− current has been suggested to generate a critical visual response upon light exposure, namely light peak (LP) 11 , 12 , 13 , which is defective in almost all BEST1 -mutated patients as shown by electrooculography (EOG) 14 , 15 . This BEST1- Cl− current- LP correlation suggests gene supplementation as a promising approach for curing bestrophinopathies. Indeed, we reported that the impaired Cl− current in RPE derived from an ARB patient bearing a BEST1 recessive mutation was rescuable by baculovirus (BV) -mediated supplementation of the WT BEST1 gene 9 . Moreover, a recent study in canine models demonstrated that the retinal abnormalities caused by recessive mutation of BEST1 can be corrected by adeno-associated virus (AAV) -mediated subretinal BEST1 gene augmentation 16 . However, the rescue efficacy of gene augmentation for BEST1 dominant mutations is still unknown. This is a very important question because firstly, most of BEST1 mutations are dominant, and secondly, it will determine whether disruption/suppression of the dominant mutant allele is necessary in therapeutic interventions. In principle, the excess of WT BEST1 could overwhelm the mutant BEST1 despite the latter being dominant over the former at a 1:1 ratio. As canines do not have BEST1 dominant mutation genotypes while Best1 knockout mice do not show any retinal phenotype or Cl− current abnormality 17 , 18 , patient-derived RPEs offer a more relevant model for testing the rescue of BEST1 dominant mutations. Here, we analyzed six BEST1 dominant mutations from BVMD patients, namely p.A10T, p.R218H, p.L234P, p.A243T, p.Q293K and p.D302A, using clinical examinations, patient-derived RPEs, electrophysiological recordings and structural models. Our results showed that these mutations are all loss-of-function with complete or partial deficiency of channel activity, while some of them affect the subcellular localization and/or Ca2+-sensitivity of BEST1. Remarkably, defective Ca2+-dependent Cl− currents in patient-derived RPE cells were restored by virus-mediated supplementation of the WT BEST1 gene in a time- and dose-dependent manner. Moreover, both dominant and recessive mutations of BEST1 are rescuable at a similar efficacy, and both BV and AAV can be used as the vector for gene delivery. Together, our findings underscore the great potential of gene augmentation therapy in treating bestrophinopathies, including those caused by BEST1 dominant mutations. Results Retinal phenotypes of six BVMD patients with different BEST1 mutations We examined six BVMD patients from unrelated families. Generalized retinal dysfunction was found in all six patients. Fundus autofluorescence imaging and optical coherence tomography (OCT) revealed vitelliform lesions located in the subretinal space, as well as serous retinal detachments and cystic fluid in the maculae area (Fig.  1 and Supplementary Fig.  S1 ). Unlike BEST1 recessive patients, whose electroretinography (ERG) and EOG results are significantly different from WT people 9 , BVMD patients display normal ERG but abnormal EOG results (Supplementary Fig.  S2 ) 19 . Click here to read entire article References Marquardt, A. et al . Mutations in a novel gene, VMD2, encoding a protein of unknown properties cause juvenile-onset vitelliform macular dystrophy (Best’s disease). Human molecular genetics 7, 1517–1525 (1998). Petrukhin, K. et al . Identification of the gene responsible for Best macular dystrophy. Nature genetics 19, 241–247 (1998). Burgess, R. et al . Biallelic mutation of BEST1 causes a distinct retinopathy in humans. American journal of human genetics 82, 19–31 (2008). Allikmets, R. et al . Evaluation of the Best disease gene in patients with age-related macular degeneration and other maculopathies. Hum Genet 104, 449–453 (1999). Kramer, F. et al . Mutations in the VMD2 gene are associated with juvenile-onset vitelliform macular dystrophy (Best disease) and adult vitelliform macular dystrophy but not age-related macular degeneration. Eur J Hum Genet 8, 286–292 (2000). Yardley, J. et al . Mutations of VMD2 splicing regulators cause nanophthalmos and autosomal dominant vitreoretinochoroidopathy (ADVIRC). Investigative ophthalmology & visual science 45, 3683–3689 (2004). Davidson, A. E. et al . Missense mutations in a retinal pigment epithelium protein, bestrophin-1, cause retinitis pigmentosa. American journal of human genetics 85, 581–592 (2009). Yang, T., Justus, S., Li, Y. & Tsang, S. H. BEST1: the Best Target for Gene and Cell Therapies. Molecular therapy: the journal of the American Society of Gene Therapy 23, 1805–1809 (2015). Li, Y. et al . Patient-specific mutations impair BESTROPHIN1′s essential role in mediating Ca2+-dependent Cl- currents in human RPE. Elife , https://doi.org/10.7554/eLife.29914 (2017). Marmorstein, A. D. et al . Bestrophin, the product of the Best vitelliform macular dystrophy gene (VMD2), localizes to the basolateral plasma membrane of the retinal pigment epithelium. Proc Natl Acad Sci USA 97, 12758–12763 (2000). Fujii, S., Gallemore, R. P., Hughes, B. A. & Steinberg, R. H. Direct evidence for a basolateral membrane Cl- conductance in toad retinal pigment epithelium. The American journal of physiology 262, C374–383 (1992). Gallemore, R. P. & Steinberg, R. H. Effects of DIDS on the chick retinal pigment epithelium. II. Mechanism of the light peak and other responses originating at the basal membrane. J Neurosci 9, 1977–1984 (1989). Gallemore, R. P. & Steinberg, R. H. Light-evoked modulation of basolateral membrane Cl- conductance in chick retinal pigment epithelium: the light peak and fast oscillation. Journal of neurophysiology 70, 1669–1680 (1993). Boon, C. J. et al . The spectrum of ocular phenotypes caused by mutations in the BEST1 gene. Progress in retinal and eye research 28, 187–205 (2009). Marmorstein, A. D., Cross, H. E. & Peachey, N. S. Functional roles of bestrophins in ocular epithelia. Progress in retinal and eye research 28, 206–226 (2009). Guziewicz, K. E. et al . BEST1 gene therapy corrects a diffuse retina-wide microdetachment modulated by light exposure. Proc Natl Acad Sci USA 115, E2839–E2848 (2018). Marmorstein, L. Y. et al . The light peak of the electroretinogram is dependent on voltage-gated calcium channels and antagonized by bestrophin (best-1). J Gen Physiol 127, 577–589 (2006). Milenkovic, A. et al . Bestrophin 1 is indispensable for volume regulation in human retinal pigment epithelium cells. Proc Natl Acad Sci USA 112, E2630–2639 (2015). Johnson, A. A. et al . Bestrophin 1 and retinal disease. Progress in retinal and eye research . https://doi.org/10.1016/j.preteyeres.2017.01.006 (2017).

Imran H Yusuf, Johannes Birtel, Morag Shanks, Penny Clouston, Susan M. Downes, Peter Charbel Issa, Robert E MacLaren Abstract Purpose : SNRNP200 is a gene recently identified as a cause of autosomal dominant retinitis pigmentosa (RP). The aim of this study was to report novel disease-associated variants and describe the retinal phenotype in patients with RP due to variants in SNRNP200, a gene encoding a ubiquitously expressed protein important in pre-mRNA splicing. Methods : A cross-sectional descriptive study involving patients identified from two tertiary referral retinal genetics clinics. 9 consecutive patients from 8 families with RP attributed to variants in SNRNP200 were included. Genetic diagnoses were established with molecular genetic testing using targeted next-generation sequencing. All patients underwent full clinical ophthalmic evaluation, retinal imaging with spectral-domain optical coherence tomography, short wavelength fundus autofluorescence (Heidelberg Spectralis) and digital colour fundus photography. Results : 9 patients were included in the study, 4 of whom were female, aged between 16 and 55 years of age. Each patient presented with symptoms and signs typical of a rod-cone dystrophy. Retinal imaging characteristics are presented in Figure 1. There was no suggestion of any systemic or syndromic features. Disease onset was commonly seen in childhood, although two patients experienced symptom onset in middle age (range 4 to 53 years). Progression of retinal degeneration was slow: 7 patients had a best corrected visual acuity of better than 20/40 in the better seeing eye at last follow-up (age 16 to 55), although two patients developed macular oedema. Molecular genetic testing revealed 2 novel variants (c.1547G>T p.(Cys516Phe) and c.2359G>A p.(Ala787Thr)) and 7 previously described variants in SNRNP200, all of which were missense variants. Both novel variants are well conserved, segregate with disease in affected families and are predicted to be disease causing in silico. Conclusions : Variants in SNRNP200 result in non-syndromic rod-cone dystrophy characterized clinically by a variable age of symptom onset with a retinal phenotype typical of RP. This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019. Read the original article.

Andrew P. Schachat MD, in Ryan's Retina, 2018 USH Interactome The USH genes encode proteins of different classes and families, including motor proteins, scaffold proteins, cell adhesion molecules and transmembrane receptor proteins. In vitro direct interaction studies between USH proteins and also localization studies in mouse models have, however, suggested functional relationships between these proteins such that an “USH interactome” has been proposed.606 In these studies, it should be noted, however, that although all the USH mouse models show severe hearing loss and vestibular dysfunction, only the Ush2A-/- mouse, shows signs of RP.607 From such work, a “multiprotein scaffold complex” model has been proposed for harmonin, whirlin, and sans. There is also evidence that harmonin and whirlin can bind all other components of the USH network, including cadherin 23, protocadherin 15, usherin, VLGR1 and myosinVIIA.569,603,608 Click here to read source article

Artur V. Cideciyan, Raghavi Sudharsan, Valérie L. Dufour, Michael, T. Massengill, Simone Iwabe, Malgorzata Swider, BriannaLisi, Alexander Sumaroka, Luis Felipe Marinho, Tatyana Appelbaum, Brian Rossmiller, William W. Hauswirth, Samuel G.Jacobson, Alfred S. Lewin, Gustavo D. Aguirre, William A. Beltran | Edited by Jeremy Nathans, Johns Hopkins University, Baltimore, MD | August 20, 2018 | 115 (36) E8547-E8556 | https://doi.org/10.1073/pnas.1805055115 Article Summary A number of gene-augmentation strategies are entering clinical trials for the treatment of inherited retinal blindness. Gene therapy for autosomal dominant diseases faces significant obstacles that include allelic heterogeneity and the potential need to silence the mutated gene. Here we show that a single-gene therapy vector that combines knockdown of the causative gene with its replacement by a resistant wild-type copy can prevent photoreceptor cell death and vision loss in a canine model of autosomal dominant retinitis pigmentosa. Read more, click here

Joanna Monika Gray ,  Harry Otway Orlans ,  Morag Shanks ,  Penny Clouston ,  Robert Elvis MacLaren   | Ophthalmic Genetics | 21 May 2018 | Volume 39(4) | pages 508-511 | doi: 10.1080/13816810.2018.1474369 Background The growing number of clinical trials currently underway for inherited retinal diseases has highlighted the importance of achieving a molecular diagnosis for all new cases presenting to hospital eye services. The male germ cell-associated kinase ( MAK ) gene encodes a cilium-associated protein selectively expressed in the retina and testis, and has recently been implicated in autosomal recessive retinitis pigmentosa (RP). Whole exome sequencing has previously identified a homozygous Alu insertion in probands with recessive RP and nonsense and missense mutations have also been reported. Materials and methods Here we describe two novel mutations in different alleles of the MAK gene in a 75-year-old British female, who had a clinical diagnosis of RP () with onset in the fourth decade and no relevant family history. The mutations were established through next generation sequencing of a panel of 111 genes associated with RP and RP-like phenotypes. Results Two novel null mutations were identified within the MAK gene. The first c.1195_1196delAC p.(Thr399fs), was a two base-pair deletion creating a frame-shift in exon 9 predicted to result in nonsense-mediated decay. The second, c.279-2A>G, involved the splice acceptor consensus site upstream of exon 4, predicted to lead to aberrant splicing. Conclusions The natural history of this individual’s RP is consistent with previously described MAK mutations, being significantly milder than that associated with other photoreceptor ciliopathies. We suggest inclusion of MAK as part of wider genetic testing in all individuals presenting with RP. Click here to buy article

with mutations in PDE6A and PDE6B Samer Khateb, MD, PhD | Marco Nassisi, MD | Kinga M. Bujakowska, PhD | Cécile Méjécase, MSc | Christel Condroyer, MSc | Aline Antonio, BA | Marine Foussard, BA | Vanessa Démontant, BA | Saddek Mohand-Saïd, MD, PhD | José-Alain Sahel, MD | Christina Zeitz, PhD | Isabelle Audo, MD, PhD | JAMA Ophthalmol | 2019 Apr 18 | 137(6) | 669-679 | doi:10.1001/jamaophthalmol.2018.6367 Key Points Question What are the functional and structural changes over time of patients with rod-cone dystrophy harboring mutations in PDE6A and PDE6B? Findings In this cohort, longitudinal, follow-up study of 54 patients with rod-cone dystrophy and mutations in PDE6A or PDE6B, progressive photoreceptor degeneration was documented. The findings reveal a similar disease course between both genetic groups with preservation of functional visual abilities at older ages. Meaning The results of this study suggest that these functional and structural findings may enable a better prognostic estimation and candidate selection for photoreceptor therapeutic rescue. Abstract Importance A precise phenotypic characterization of retinal dystrophies is needed for disease modeling as a basis for future therapeutic interventions. Objective To compare genotype, phenotype, and structural changes in patients with rod-cone dystrophy (RCD) associated with mutations in PDE6A or PDE6B. To read more of the source article, click here.