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Robert E. Maclaren - One of the best experts on this subject based on the ideXlab platform.

  • Low-contrast visual acuity versus low-luminance visual acuity in Choroideremia.
    Clinical & experimental optometry, 2021
    Co-Authors: Laura J Wood, Jasleen K. Jolly, Colm Andrews, Iain R Wilson, Doron G. Hickey, Jasmina Cehajic-kapetanovic, Robert E. Maclaren
    Abstract:

    Choroideremia is a progressive X‐linked inherited rod‐cone dystrophy. Patients present with nyctalopia and progressive visual field loss, but visual acuity remains well preserved early on. This stu...

  • a distinct retinal pigment epithelial cell autofluorescence pattern in Choroideremia predicts early involvement of overlying photoreceptors
    Acta Ophthalmologica, 2020
    Co-Authors: Marta Stevanovic, Jasleen K. Jolly, Jasmina Cehajic Kapetanovic, Robert E. Maclaren
    Abstract:

    PURPOSE Choroideremia is an X-linked retinal disease characterized by early retinal pigment epithelium (RPE) loss and subsequent retinal degeneration. The RPE adopts either a smooth or mottled appearance on fundus autofluorescence (FAF). It is not known how RPE changes predict the health of the overlying ellipsoid zone (EZ). METHODS A retrospective review of FAF and optical coherence tomography (OCT) images from 20 patients with Choroideremia was performed. The percentage of intact EZ in each smooth and mottled FAF region was determined using one horizontal trans-foveal OCT section. RESULTS Fourteen out of 20 patients had distinct smooth and mottled areas in both eyes and were included in the sub-analysis. On average, 62.5 ± 10.1% of the EZ in each smooth region of the right eyes was intact compared to 10.0 ± 4.3% in the mottled areas. The same trend was observed in left eyes: 76.5 ± 7.2% of the EZ was intact in the smooth regions versus 9.8 ± 3.9% in the mottled areas (two-way anova, p < 0.0001). Thus, the mottled FAF regions were associated with EZ disruption more so than the smooth areas. CONCLUSION Retinal pigment epithelium (RPE) changes correlate with the health of the overlying EZ in Choroideremia. The smooth FAF region likely represents early stages of the disease, with most of the area containing preserved EZ, whereas the mottled zone indicates more advanced stages and has mostly disrupted EZ. Because of the clear relationship between FAF findings and EZ integrity, FAF imaging can be used to monitor disease progression and identify areas of preserved EZ that could be rescued by gene therapy.

  • association of messenger rna level with phenotype in patients with Choroideremia potential implications for gene therapy dose
    JAMA Ophthalmology, 2020
    Co-Authors: Lewis E Fry, Alun R Barnard, Maria I. Patrício, Jonathan H. Williams, Penny Clouston, James Aylward, Harriet Hewitt, Kanmin Xue, Robert E. Maclaren
    Abstract:

    Importance Gene therapy is a promising treatment for Choroideremia, an X-linked retinal degeneration. The required minimum level of gene expression to ameliorate degeneration rate is unknown. This can be interrogated by exploring the association between messenger RNA (mRNA) levels and phenotype in mildly affected patients with Choroideremia. Objective To analyzeCHMmRNA splicing outcomes in 2 unrelated patients with the same c.940+3delACHMsplice site variant identified as mildly affected from a previous study of patients with Choroideremia. Design, Setting, and Participants In this retrospective observational case series, 2 patients with c.940+3delACHMvariants treated at a single tertiary referral center were studied. In addition, a third patient with a c.940+2T>A variant that disrupts the canonical dinucleotide sequence at the same donor site served as a positive control. Data were collected from October 2013 to July 2018. Main Outcomes and Measures Central area of residual fundus autofluorescence was used as a biomarker for disease progression.CHMtranscript splicing was assessed by both end point and quantitative polymerase chain reaction. Rab escort protein 1 (REP1) expression was assessed by immunoblot. Results The 2 mildly affected patients with c.940+3delA variants had large areas of residual autofluorescence for their age and longer degeneration half-lives compared with the previous cohort of patients with Choroideremia. The control patient with a c.940+2T>A variant had a residual autofluorescence area within the range expected for his age. Both patients with the c.940+3delA variant expressed residual levels of full-lengthCHMmRNA transcripts relative to the predominant truncated transcript (mean [SEM] residual level: patient 1, 2.3% [0.3]; patient 2, 4.7% [0.2]), equivalent to approximately less than 1% of the level of full-lengthCHM expressed in nonaffected individuals. Full-lengthCHM expression was undetectable in the control patient. REP1 expression was less than the threshold for detection both in patients 1 and 2 and the control patient compared with wild-type controls. Conclusions and Relevance These results demonstrate the first genotype-phenotype association in Choroideremia. A +3 deletion in intron 7 is sufficient to cause Choroideremia in a milder form. If replicated with gene therapy, these findings would suggest that relatively low expression (less than 1%) of the wild-type levels of mRNA would be sufficient to slow disease progression.

  • optimisation of dark adaptation time required for mesopic microperimetry
    British Journal of Ophthalmology, 2019
    Co-Authors: Ruofan Connie Han, Robert E. Maclaren, Joanna Monika Gray, Jennie Han, Jasleen K. Jolly
    Abstract:

    Background Macular Integrity Assessment (MAIA) microperimetry is increasingly used in clinical and research settings to assess point retinal sensitivity and fixation stability. Testing occurs under mesopic conditions, commonly after a period of dark adaptation. Our aim was to identify the minimum length of adaptation required to optimise microperimetry performance. Methods MAIA microperimetry using the 10-2 grid was performed on 40 right eyes of 40 healthy participants aged 18–73 with no ocular pathology and vision of at least 0.1 logMAR after ambient light exposure, with 0, 5, 10, 15, 20 and 30 min of adaptation in mesopic settings. Ten right eyes of 10 participants with Choroideremia were also tested following 0 and 20 min of adaptation. We further tested 10 right eyes of 10 healthy participants after bright light exposure, with 0, 10 and 20 min of adaptation. We compared changes in threshold sensitivity and fixation stability across time points. Results Microperimetry performance did not improve with increasing adaptation time in healthy participants or patients with Choroideremia after ambient light exposure. After bright light exposure, we found microperimetry thresholds improved after 10 min of adaptation, but did not improve further at 20 min. Conclusion Mesopic adaptation is not required before MAIA microperimetry after exposure to ambient light. Ten minutes of adaptation is sufficient after exposure to a bright light stimulus, such as ophthalmoscopy or retinal imaging. The brief time of dark adaptation required corresponds to cone adaptation curves and provides further evidence for cone-mediated central retinal function under mesopic conditions.

  • The Biological Activity of AAV Vectors for Choroideremia Gene Therapy Can Be Measured by In Vitro Prenylation of RAB6A
    Elsevier, 2018
    Co-Authors: Maria I. Patrício, Alun R Barnard, Christopher I. Cox, Clare Blue, Robert E. Maclaren
    Abstract:

    Choroideremia (CHM) is a rare, X-linked recessive retinal dystrophy caused by mutations in the CHM gene. CHM is ubiquitously expressed in human cells and encodes Rab escort protein 1 (REP1). REP1 plays a key role in intracellular trafficking through the prenylation of Rab GTPases, a reaction that can be reproduced in vitro. With recent advances in adeno-associated virus (AAV) gene therapy for CHM showing gene replacement to be a promising approach, an assay to assess the biological activity of the vectors is of the uttermost importance. Here we sought to compare the response of two Rab proteins, RAB27A and RAB6A, to the incorporation of a biotinylated lipid donor in a prenylation reaction in vitro. First, we found the expression of REP1 to be proportional to the amount of recombinant AAV (rAAV)2/2-REP1 used to transduce the cells. Second, prenylation of RAB6A appeared to be more sensitive to REP1 protein expression than prenylation of RAB27A. Moreover, the method was reproducible in other cell lines. These results support the further development of a prenylation reaction using a biotinylated lipid donor and RAB6A to assess the biological activity of AAV vectors for CHM gene therapy. Keywords: AAV gene therapy, Choroideremia, prenylation, potency assa

Re Maclaren - One of the best experts on this subject based on the ideXlab platform.

  • Low luminance visual acuity and low luminance deficit in Choroideremia and RPGR-associated retinitis pigmentosa
    'Association for Research in Vision and Ophthalmology (ARVO)', 2021
    Co-Authors: Lj Wood, Re Maclaren, As Josan, Buckley Tmw, Jk Jolly
    Abstract:

    Introduction: Choroideremia and RPGR-associated retinitis pigmentosa (RP) are two distinct inherited rod-cone degenerations, where good visual acuity (VA) is maintained until late disease stages, limiting its usefulness as a disease marker. Low luminance VA and low luminance deficit (standard VA minus low luminance VA) may be more sensitive visual function measures. Methods: Standard VA was obtained using Early Treatment Diabetic Retinopathy Study letter charts (Precision Vision, Bloomington, IL, USA). Low luminance VA was assessed using a 2.0-log unit neutral density filter, with the same chart setup, without formal dark adaptation. Mean central retinal sensitivity was assessed using MAIA microperimetry (Centervue SpA, Padova, Italy). Optical coherence tomography imaging was attained with Heidelberg Eye Explorer software (Heidelberg Engineering, Heidelberg, Germany). Results: Twenty-four male participants with confirmed pathogenic RPGR mutations, 44 male participants with confirmed pathogenic CHM mutations, and 62 age-matched controls underwent clinical assessment prior to clinical trial recruitment. Low luminance VA was significantly reduced in both disease groups compared to controls. The low luminance deficit correlated with microperimetry retinal sensitivity and ellipsoid zone width. Eleven participants with moderate VA had poor low luminance VA (subsequently a large low luminance deficit), no detectable microperimetry sensitivity, and severely constricted ellipsoid zone widths. Conclusions:Low luminance VA and subsequently low luminance deficit are useful markers of central macular visual function in both Choroideremia and RPGR-associated RP, when standard VA is preserved. Translational Relevance: Low luminance visual acuity and low luminance deficit are useful vision measures in two distinct rod-cone degenerations and may be useful in other retinal degenerations

  • Potential lifetime quality of life benefits of Choroideremia gene therapy: projections from a clinically informed decision model
    'Springer Science and Business Media LLC', 2019
    Co-Authors: Halioua-haubold C-l, Jk Jolly, Ja Smith, Pinedo Villanueva R, Da Brindley, Re Maclaren
    Abstract:

    Background The first gene therapy for an inherited retinal dystrophy recently received market approval in the United States; multiple other gene therapies are in the clinical pipeline. Thus far, gene therapy has commanded prices in the range of USD 500,000 to over USD 1,000,000 for the one-time doses and have been indicated for highly orphan diseases where there is no other viable treatment option. To be adopted by healthcare systems, gene therapy will need to show clinical benefit in line with its increased costs. Before longitudinal patient studies are available, model-based estimations will be necessary to project the full clinical benefit of gene therapy. Methods To investigate the lifetime benefit of gene therapy for the retinal dystrophy Choroideremia, we have built a Markov model of disease progression informed by clinical data of AAV.REP1 and voretigene neparvovec (Luxturna, Spark Therapeutics). Gene therapy patient benefit was estimated by quality-adjusted life years (QALYs) in three hypothetical disease severity patient groups. The severity of disease was defined by the combined effect of remaining retinal area and visual acuity and assigned corresponding health utility values. Results Early-stage patients treated with gene therapy were estimated to gain, in average, 14.30 QALYs over standard-of-care, mid-stage patients 6.22 QALYs, and late-stage patients 1.48 QALYs over untreated patients during their lifetime owing to treatment. Cost-effectiveness was not assessed as AAV.REP1 is still in clinical trials. Conclusions In young adults in the earlier stages of Choroideremia, successful gene therapy is expected to provide a significant increase in health-related quality of life.

  • The impact of progressive visual field constriction on reading ability in an inherited retinal degeneration
    'S. Karger AG', 2019
    Co-Authors: Jk Jolly, Xue K, Ce Couldridge-smith, Re Maclaren
    Abstract:

    Background: The ability to read is an important factor in the quality of life. Choroideremia is an inherited retinal degeneration presenting with gradual, progressive constriction of the central visual field, providing a useful disease model to investigate the impact of the visual field on reading ability. Objective: The aim of this study was to provide practical guidance on the usefulness of measuring reading ability in patients.Method: The Radner Reading Test was administered to 33 patients (65 eyes with Choroideremia). To quantify the residual retinal area, the patients underwent microperimetry and imaging. The visual angle subtended by the largest letter read by each subject was calculated using Emsley’s Model Eye. Results: A minimum of 1 letter must be seen to allow the eye to read, with preservation of foveal sensitivity. The relationship between reading speed and acuity varies with the visual field. The reading speed is higher in eyes with an intact fovea (p Conclusions: In order to read, an eye must have enough retinal width close to the fovea to see at least 1 full letter. Direction of print does not impact the ability to read, allowing results from different languages to be combined in clinical trials.

  • VASCULAR ALTERATIONS REVEALED WITH OPTICAL COHERENCE TOMOGRAPHY ANGIOGRAPHY IN PATIENTS WITH Choroideremia
    'Ovid Technologies (Wolters Kluwer Health)', 2019
    Co-Authors: Battaglia Parodi M, Re Maclaren, Arrigo A, Aragona E, Toto L, Mastropasqua R, Mp Manitto, Bandello F.
    Abstract:

    PURPOSE: Choroideremia is a rare degenerative retinal disease that causes incurable blindness. It occurs as a result of the deficiency of the X-linked CHM gene, which encodes the Rab escort protein 1 (REP1). Gene therapy has been developed to treat CHM using adeno-associated viral vectors and is currently undergoing clinical trials. Expression of the CHM gene is ubiquitous throughout the retina, and it is therefore important to identify which retinal layers are affected in the disease process. The purpose of this study was to assess in particular the choriocapillaris using optical coherence tomography angiography because this layer is difficult to see with conventional imaging techniques. METHODS: Six men with Choroideremia were identified and underwent standardized optical coherence tomography angiography as part of an ethics-approved clinical study and were compared with age-matched control subjects. RESULTS: The choriocapillaris appeared normal in regions where the retinal pigment epithelium remained intact, but it was deficient elsewhere. The outer retinal vasculature showed significant changes peripherally but also some changes centrally. The inner retinal vasculature appeared unaffected by the disease process. CONCLUSION: Choroideremia is a disease in which the choriocapillaris maintains a normal structure until the loss of the overlying retinal pigment epithelium. The inner retina also appears not to be affected at the vascular level. Although this study is limited by the small number of patients eligible for inclusion in the study, the observations support the concept of targeting gene therapy to the retinal pigment epithelium and outer retina because there is no evidence of independent degeneration of the choriocapillaris

  • Retinal degeneration in Choroideremia follows an exponential decay function
    'Elsevier BV', 2018
    Co-Authors: Jw Aylward, Mi Patricio, Xue K, Jk Jolly, Jc Wood, Brett J, Km Jasani, Re Maclaren
    Abstract:

    Fundus autofluorescence (AF) arises from lipofuscin, which is derived from retinoid byproducts of the visual cycle and accumulates within retinal pigment epithelial cells. Alterations in AF pattern are seen in a wide range of retinal degenerations. Choroideremia is an X-linked retinal dystrophy caused by loss-of-function mutations within the CHM gene, encoding Rab escort protein-1. It is uniquely characterized by a central “island” of residual AF that undergoes gradual shrinkage with disease progression. The decrease in AF area is correlated precisely with loss of overlying photoreceptors, leading to progressive visual field restriction and blindness around the fifth decade. Retinal gene replacement therapy using an adeno-associated viral vector could potentially slow down or stop disease progression in Choroideremia. Although visual acuity may be improved by gene therapy, it is affected relatively late in the disease; therefore, the area of residual AF may provide an alternative anatomic biomarker for monitoring progression at earlier stages. A previous cross-sectional study suggested an exponential decrease in AF area with age in Choroideremia. However, longitudinal data on natural disease progression is lacking. For instance, it is uncertain whether individuals progressed at different rates depending on genetic, epigenetic, or environmental factors, and whether the rate of progression varied between early and late stages of the disease

Miguel C. Seabra - One of the best experts on this subject based on the ideXlab platform.

  • Functional expression of Rab escort protein 1 following AAV2-mediated gene delivery in the retina of Choroideremia mice and human cells ex vivo
    Journal of Molecular Medicine, 2013
    Co-Authors: Tanya Tolmachova, Robert E. Maclaren, Alun R Barnard, Oleg E. Tolmachov, Samantha R. Silva, Daniel M. Lipinski, Nathan J. Walker, Miguel C. Seabra
    Abstract:

    Choroideremia (CHM) is an X-linked retinal degeneration of photoreceptors, the retinal pigment epithelium (RPE) and choroid caused by loss of function mutations in the CHM / REP1 gene that encodes Rab escort protein 1. As a slowly progressing monogenic retinal degeneration with a clearly identifiable phenotype and a reliable diagnosis, CHM is an ideal candidate for gene therapy. We developed a serotype 2 adeno-associated viral vector AAV2/2-CBA-REP1, which expresses REP1 under control of CMV-enhanced chicken β-actin promoter (CBA) augmented by a Woodchuck hepatitis virus post-transcriptional regulatory element. We show that the AAV2/2-CBA-REP1 vector provides strong and functional transgene expression in the D17 dog osteosarcoma cell line, CHM patient fibroblasts and CHM mouse RPE cells in vitro and in vivo. The ability to transduce human photoreceptors highly effectively with this expression cassette was confirmed in AAV2/2-CBA-GFP transduced human retinal explants ex vivo. Electroretinogram (ERG) analysis of AAV2/2-CBA-REP1 and AAV2/2-CBA-GFP-injected wild-type mouse eyes did not show toxic effects resulting from REP1 overexpression. Subretinal injections of AAV2/2-CBA-REP1 into CHM mouse retinas led to a significant increase in a- and b-wave of ERG responses in comparison to sham-injected eyes confirming that AAV2/2-CBA-REP1 is a promising vector suitable for Choroideremia gene therapy in human clinical trials.

  • retinal pigment epithelium defects accelerate photoreceptor degeneration in cell type specific knockout mouse models of Choroideremia
    Investigative Ophthalmology & Visual Science, 2010
    Co-Authors: Tanya Tolmachova, Miguel C. Seabra, Robert E. Maclaren, Silene T Wavreshapton, Alun R Barnard, Clare E Futter
    Abstract:

    Purpose. Choroideremia (CHM) is a progressive X-linked degeneration of three ocular layers (photoreceptors, retinal pigment epithelium, and choroid), with a complex and still largely unclear pathogenesis. To investigate the pathophysiology of CHM, the authors engineered mice with a cell type–specific Chm/Rep1 knockout (KO).

  • deficient geranylgeranylation of ram rab27 in Choroideremia
    Journal of Biological Chemistry, 1995
    Co-Authors: Miguel C. Seabra, Janmeet S. Anant
    Abstract:

    Choroideremia, an X-linked form of retinal degeneration, results from defects in the Rab escort protein-1 (REP-1) gene. REP-1 and REP-2 assist in the attachment of geranylgeranyl groups to Rab GTPases, a modification essential for their action as molecular switches regulating intracellular vesicular transport. If Rabs that depend preferentially on REP-1 for prenylation exist, they will accumulate unprenylated in Choroideremia cells. Using recombinant Rab geranylgeranyl transferase and REPs to label unprenylated cytosolic proteins, we identified one unprenylated protein in Choroideremia lymphoblasts that was prenylated in vitro more efficiently by REP-1 than by REP-2. This protein was purified and identified as Ram (renamed Rab27), a previously cloned Rab of unknown function. Immunohistochemistry of rat retina showed that Ram/Rab27 is expressed in the pigment epithelium and choriocapillaris, the two retinal cell layers that degenerate earliest in Choroideremia. These results raise the possibility that the retinal degeneration in Choroideremia results from the deficient geranylgeranylation of Ram/Rab27 or a closely related protein.

  • rep 2 a rab escort protein encoded by the Choroideremia like gene
    Journal of Biological Chemistry, 1994
    Co-Authors: Frans P M Cremers, Miguel C. Seabra, Michael S Brown, Scott A Armstrong, Joseph L Goldstein
    Abstract:

    Rab escort proteins (REPs) bind to newly synthesized Rab proteins and remain bound during and after the attachment of a geranylgeranyl (GG) group by the catalytic component of the Rab GG transferase. Transfer of the GG group is absolutely dependent on the participation of a REP. REP-1, the first characterized REP, is produced by a gene on the X chromosome that is defective in patients with Choroideremia, a form of retinal degeneration. Cremers et al. (Cremers, F.P.M., Molloy, C. M., van de Pol, D. J. R., van den Hurk, J. A. J. M., Bach, I., Geurts van Kessel, A. H. M., and Ropers, H.-H. (1992) Hum. Mol. Genet. 1, 71-75) isolated a related gene, designated Choroideremia-like, which encodes a protein that closely resembles REP-1. In the current studies, we produced REP-1 and REP-2 by recombinant DNA methods and showed that both proteins were approximately equal in facilitating the attachment of GG groups to several Rab proteins, including Rab1A, Rab5A, and Rab6. However, REP-2 was only 25% as active as REP-1 in supporting GG attachment to Rab3A and Rab3D. The low activity toward Rab3A was increased to that of Rab1A when the COOH-terminal 12 amino acids of Rab3A were replaced with the corresponding residues of Rab1A. We suggest that REP-2 substitutes for the absent function of REP-1 in nonretinal cells of patients with Choroideremia, thus preventing cellular dysfunction throughout the body. In the retina, REP-2 may be only partially effective, leading eventually to retinal degeneration and blindness.

  • cdna cloning of component a of rab geranylgeranyl transferase and demonstration of its role as a rab escort protein
    Cell, 1993
    Co-Authors: Douglas A Andres, Miguel C. Seabra, Michael S Brown, Scott A Armstrong, Tor E Smeland, Frans P M Cremers, Joseph L Goldstein
    Abstract:

    cDNA cloning of component A of rat Rab geranylgeranyl transferase confirms identity of the protein with the human Choroideremia gene product and its resemblance to Rab3A guanine nucleotide dissociation inhibitor (GDI), which binds prenylated Rabs. In biochemical assays we demonstrate that component A binds unprenylated Rab1A, presents it to the catalytic component B, and remains bound to it after the geranylgeranyl transfer reaction. In the absence of detergents, the reaction terminates when all of component A is occupied with prenylated Rab. Detergents allow multiple rounds of catalysis, apparently by dissociating the component A-Rab complex and thus allowing recycling of component A. Within the cell, component A may be regenerated by transferring its prenylated Rab to a protein acceptor, such as Rab3A GDI. In view of its function in escorting Rab proteins during and presumably after the prenyl transfer reaction, we propose to rename component A as Rab escort protein (REP). A genetic defect in REP underlies human Choroideremia, a disease of retinal degeneration.

Ian M Macdonald - One of the best experts on this subject based on the ideXlab platform.

  • Visual Psychophysics and Physiological Optics Microperimetry as an Outcome Measure in Choroideremia Trials: Reproducibility and Beyond
    2016
    Co-Authors: Ioannis S Dimopoulos, Calvin Tseng, Ian M Macdonald
    Abstract:

    Citation: Dimopoulos IS, Tseng C, MacDonald IM. Microperimetry as an outcome measure in Choroideremia trials: reproducibility and beyond. Invest Ophthalmol Vis Sci. 2016;57:4151-4161. DOI:10.1167/ iovs.16-19338 PURPOSE. To determine test-retest repeatability of microperimetry testing (MP) in Choroideremia (CHM) subjects using standard and personalized stimulus grids. METHODS. Fifteen CHM subjects (28 eyes) underwent consecutive repeat examinations with the Macular Integrity Assessment (MAIA) microperimeter using a standard (108) and a customized macular grid adapted to individual macular pathology. Repeatability of standardgrid mean (MS) and point-wise (PWS) sensitivity was determined and compared with agematched controls (seven eyes), with PWS separately analyzed for loci within and outside the border of degeneration. Interpolated volumetric indices were used to estimate repeatability of customized grids and compare their performance to standard grids. RESULTS. Test-retest measures of standard-grid MS yielded higher coefficients of variation (CV) in CHM subjects compared with controls (0.09 vs. 0.02). Volumetric indices from customized grids improved repeatability by driving CV values to 0.05 and close to 0.02 for region-ofinterest (ROI) analysis. Variability of PWS was significantly higher in CHM, especially at the border of degeneration (10.68 vs. 4.74 dB at the central retina, P < 0.001). CONCLUSIONS. Microperimetry testing in CHM shows high test-retest variation at the border of degeneration, which influences repeatability of MS measures. Volumetric measures from customized grids can improve reliability of both global and regional sensitivity assessment. Nevertheless, inherent test-retest variation of individual points needs to be taken into account when assessing potential functional decline and/or disease progression

  • loss of function mutations in rab escort protein 1 rep 1 affect intracellular transport in fibroblasts and monocytes of Choroideremia patients
    PLOS ONE, 2009
    Co-Authors: Natalia V Strunnikova, Jennifer Barb, Yuri V Sergeev, Ashwin Thiagarajasubramanian, Christopher Silvin, Peter J Munson, Ian M Macdonald
    Abstract:

    Background Choroideremia (CHM) is a progressive X-linked retinopathy caused by mutations in the CHM gene, which encodes Rab escort protein-1 (REP-1), an escort protein involved in the prenylation of Rabs. Under-prenylation of certain Rabs, as a result of loss of function mutations in REP-1, could affect vesicular trafficking, exocytosis and secretion in peripheral cells of CHM patients.

  • detection of localized retinal dysfunction in a Choroideremia carrier
    American Journal of Ophthalmology, 2004
    Co-Authors: Marsha C Cheung, Ian M Macdonald, George Nune, Min Wang, Kerry E Mctaggart, Jacque L Duncan
    Abstract:

    Abstract Purpose To investigate severe unilateral vision loss in a Choroideremia carrier. Design Case report. Methods Ocular examination, genetic testing, Humphrey visual fields, full-field and multifocal (mf) electroretinogram (ERG) tests were used to study a family with Choroideremia. Results In a carrier with unilateral central vision loss, mfERG showed severely reduced amplitudes which correlated with a band of retinal pigment epithelial and choroidal atrophy in the macula, a dense central scotoma on Humphrey visual fields testing, and decreased ERG amplitudes. Conclusions Multifocal ERG may be a sensitive tool to measure functional abnormalities in Choroideremia carriers. Mosaic inactivation of the normal gene may cause expression of the mutation with severe vision loss in Choroideremia carriers.

Alun R Barnard - One of the best experts on this subject based on the ideXlab platform.

  • association of messenger rna level with phenotype in patients with Choroideremia potential implications for gene therapy dose
    JAMA Ophthalmology, 2020
    Co-Authors: Lewis E Fry, Alun R Barnard, Maria I. Patrício, Jonathan H. Williams, Penny Clouston, James Aylward, Harriet Hewitt, Kanmin Xue, Robert E. Maclaren
    Abstract:

    Importance Gene therapy is a promising treatment for Choroideremia, an X-linked retinal degeneration. The required minimum level of gene expression to ameliorate degeneration rate is unknown. This can be interrogated by exploring the association between messenger RNA (mRNA) levels and phenotype in mildly affected patients with Choroideremia. Objective To analyzeCHMmRNA splicing outcomes in 2 unrelated patients with the same c.940+3delACHMsplice site variant identified as mildly affected from a previous study of patients with Choroideremia. Design, Setting, and Participants In this retrospective observational case series, 2 patients with c.940+3delACHMvariants treated at a single tertiary referral center were studied. In addition, a third patient with a c.940+2T>A variant that disrupts the canonical dinucleotide sequence at the same donor site served as a positive control. Data were collected from October 2013 to July 2018. Main Outcomes and Measures Central area of residual fundus autofluorescence was used as a biomarker for disease progression.CHMtranscript splicing was assessed by both end point and quantitative polymerase chain reaction. Rab escort protein 1 (REP1) expression was assessed by immunoblot. Results The 2 mildly affected patients with c.940+3delA variants had large areas of residual autofluorescence for their age and longer degeneration half-lives compared with the previous cohort of patients with Choroideremia. The control patient with a c.940+2T>A variant had a residual autofluorescence area within the range expected for his age. Both patients with the c.940+3delA variant expressed residual levels of full-lengthCHMmRNA transcripts relative to the predominant truncated transcript (mean [SEM] residual level: patient 1, 2.3% [0.3]; patient 2, 4.7% [0.2]), equivalent to approximately less than 1% of the level of full-lengthCHM expressed in nonaffected individuals. Full-lengthCHM expression was undetectable in the control patient. REP1 expression was less than the threshold for detection both in patients 1 and 2 and the control patient compared with wild-type controls. Conclusions and Relevance These results demonstrate the first genotype-phenotype association in Choroideremia. A +3 deletion in intron 7 is sufficient to cause Choroideremia in a milder form. If replicated with gene therapy, these findings would suggest that relatively low expression (less than 1%) of the wild-type levels of mRNA would be sufficient to slow disease progression.

  • The Biological Activity of AAV Vectors for Choroideremia Gene Therapy Can Be Measured by In Vitro Prenylation of RAB6A
    Elsevier, 2018
    Co-Authors: Maria I. Patrício, Alun R Barnard, Christopher I. Cox, Clare Blue, Robert E. Maclaren
    Abstract:

    Choroideremia (CHM) is a rare, X-linked recessive retinal dystrophy caused by mutations in the CHM gene. CHM is ubiquitously expressed in human cells and encodes Rab escort protein 1 (REP1). REP1 plays a key role in intracellular trafficking through the prenylation of Rab GTPases, a reaction that can be reproduced in vitro. With recent advances in adeno-associated virus (AAV) gene therapy for CHM showing gene replacement to be a promising approach, an assay to assess the biological activity of the vectors is of the uttermost importance. Here we sought to compare the response of two Rab proteins, RAB27A and RAB6A, to the incorporation of a biotinylated lipid donor in a prenylation reaction in vitro. First, we found the expression of REP1 to be proportional to the amount of recombinant AAV (rAAV)2/2-REP1 used to transduce the cells. Second, prenylation of RAB6A appeared to be more sensitive to REP1 protein expression than prenylation of RAB27A. Moreover, the method was reproducible in other cell lines. These results support the further development of a prenylation reaction using a biotinylated lipid donor and RAB6A to assess the biological activity of AAV vectors for CHM gene therapy. Keywords: AAV gene therapy, Choroideremia, prenylation, potency assa

  • Gene Therapy for Choroideremia Using an Adeno-Associated Viral (AAV) Vector
    2016
    Co-Authors: Alun R Barnard, Robert E. Maclaren
    Abstract:

    Choroideremia is an outer retinal degeneration with a characteristic clinical appearance that was first described in the nineteenth century. The disorder begins with reduction of night vision and gradually progresses to blindness bymiddle age. The appearance of the fundus in sufferers is recognizable by the characteristic pale color caused by the loss of the outer retina, retinal-pigmented epithelium, and choroidal vessels, leading to exposure of the underlying sclera. Choroideremia shows X-linked recessive inheritance and the Choroideremia gene (CHM) was one of the first to be identified by positional cloning in 1990. Subsequent identification and characterization of the CHM gene, which encodes Rab escort protein 1 (REP1), has led to better comprehension of the disease and enabled advances in genetic diagnosis. Despite several decades of work to understand the exact pathogenesis, no estab-lished treatments currently exist to stop or even slow the progression of retinal degeneration in Choroideremia. Encouragingly, several specific molecular and clinical features make Choroideremia an ideal candidate for treatment with gene therapy. This work describes the considerations and challenges in the development of a new clinical trial using adeno-asso-ciated virus (AAV) encoding the CHM gene

  • visual acuity after retinal gene therapy for Choroideremia
    The New England Journal of Medicine, 2016
    Co-Authors: Thomas L. Edwards, Andrew R Webster, Graeme C M Black, Jasleen K. Jolly, Tanya Tolmachova, Alun R Barnard, Markus Groppe, Charles L Cottriall, Andrew J Lotery, Graham E Holder
    Abstract:

    In this study, the subfoveal injection of a gene-therapy vector carrying nonmutated CHM, the gene that, when mutated, causes a form of blindness called Choroideremia, was followed by an improvement in visual acuity in two of six patients at 3.5 years after injection.

  • retinal gene therapy in patients with Choroideremia initial findings from a phase 1 2 clinical trial
    The Lancet, 2014
    Co-Authors: Robert E. Maclaren, Tanya Tolmachova, Alun R Barnard, Markus Groppe, Charles L Cottriall, L Seymour, Reed K Clark, Mj During
    Abstract:

    Summary Background Choroideremia is an X-linked recessive disease that leads to blindness due to mutations in the CHM gene, which encodes the Rab escort protein 1 (REP1). We assessed the effects of retinal gene therapy with an adeno-associated viral (AAV) vector encoding REP1 (AAV.REP1) in patients with this disease. Methods In a multicentre clinical trial, six male patients (aged 35–63 years) with Choroideremia were administered AAV.REP1 (0·6–1·0×10 10 genome particles, subfoveal injection). Visual function tests included best corrected visual acuity, microperimetry, and retinal sensitivity tests for comparison of baseline values with 6 months after surgery. This study is registered with ClinicalTrials.gov, number NCT01461213. Findings Despite undergoing retinal detachment, which normally reduces vision, two patients with advanced Choroideremia who had low baseline best corrected visual acuity gained 21 letters and 11 letters (more than two and four lines of vision). Four other patients with near normal best corrected visual acuity at baseline recovered to within one to three letters. Mean gain in visual acuity overall was 3·8 letters (SE 4·1). Maximal sensitivity measured with dark-adapted microperimetry increased in the treated eyes from 23·0 dB (SE 1·1) at baseline to 25·3 dB (1·3) after treatment (increase 2·3 dB [95% CI 0·8–3·8]). In all patients, over the 6 months, the increase in retinal sensitivity in the treated eyes (mean 1·7 [SE 1·0]) was correlated with the vector dose administered per mm 2 of surviving retina ( r =0·82, p=0·04). By contrast, small non-significant reductions (p>0·05) were noted in the control eyes in both maximal sensitivity (–0·8 dB [1·5]) and mean sensitivity (–1·6 dB [0·9]). One patient in whom the vector was not administered to the fovea re-established variable eccentric fixation that included the ectopic island of surviving retinal pigment epithelium that had been exposed to vector. Interpretation The initial results of this retinal gene therapy trial are consistent with improved rod and cone function that overcome any negative effects of retinal detachment. These findings lend support to further assessment of gene therapy in the treatment of Choroideremia and other diseases, such as age-related macular degeneration, for which intervention should ideally be applied before the onset of retinal thinning. Funding UK Department of Health and Wellcome Trust.