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.
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.
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.
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.
Optical coherence tomography angiography revealed profound alterations of both deep capillary plexus and choriocapillaris in patients with choroideremia; in contrast, the superficial capillary plexus was preserved. Moreover, en face images provided useful contributions in the description of the morphologic features of outer retinal tubulations.
*Department of Ophthalmology, IRCCS Ospedale San Raffaele, University Vita-Salute, Milan, Italy;
†Oxford Eye Hospital, Oxford University Hospitals NHS Foundation Trust, Oxford, United Kingdom; and
‡Ophthalmology Clinic, Department of Medicine and Science of Ageing, University G. D'Annunzio Chieti-Pescara, Chieti, Italy.
Reprint requests: Alessandro Arrigo, MD, Department of Ophthalmology, IRCCS Ospedale San Raffaele, University Vita-Salute, via Olgettina 60, Milan, 20132, Italy; e-mail: firstname.lastname@example.org
R. E. MacLaren received funding from the Oxford NIHR Biomedical Research Centre and the Medical Research Council United Kingdom.
F. Bandello is a consultant for Alcon (Fort Worth, TX), Alimera Sciences (Alpharetta, GA), Allergan, Inc (Irvine, CA), Farmila-Thea (Clermont-Ferrand, France), Bayer Shering-Pharma (Berlin, Germany), Bausch & Lomb (Rochester, NY), Genentech (San Francisco, CA), Hoffmann-La-Roche (Basel, Switzerland), NovagaliPharma (Évry, France), Novartis (Basel, Switzerland), Sanofi-Aventis (Paris, France), Thrombogenics (Heverlee, Belgium), and Zeiss (Dublin, OH). R. E. MacLaren is the scientific founder and director of Nightstarx, Ltd, a retinal gene therapy company established by the University of Oxford and the Wellcome Trust in London. Nightstar had no role in the conduct or write up of this study.