Flicker cone function in normal and day blind sheep: a large animal model for human achromatopsia caused by CNGA3 mutation

Abstract

Purpose Recently we reported on day blindness in sheep caused by a mutation in the CNGA3 gene, thus making affected sheep a naturally occurring large animal model for therapeutic intervention in CNGA3 achromatopsia patients. The purpose of this study was to characterize flicker cone function in normal and day blind sheep, with the aim of generating a normative data base for ongoing gene therapy studies. Methods Electoretinographic (ERG) cone responses were evoked with full-field conditions in 10 normal, 6 heterozygous carriers and 36 day blind sheep. Following light adaptation (10 min, 30 cd/m2), responses were recorded at four increasing light intensities (1, 2.5, 5 and 10 cd s/m2). At each of these intensities, a single photopic flash response followed by 8 cone flicker responses (10–80 Hz) was recorded. Results were used to generate a normative data base for the three groups. Differences between day blind and normal control animals were tested in two age-matched groups (n = 10 per group). Results The normal sheep cone ERG wave is bipartite in nature, with critical flicker fusion frequency (CFF) >80 Hz. In all four flash intensities, the single photopic flash a-wave and b-wave amplitudes were significantly lower (p < 0.005), and implicit times significantly delayed (p < 0.0001), in day blind animals. In all four flash intensities, CFF values were significantly lower (p < 0.0001) in day blind sheep. Conclusions Cone function is severely depressed in day blind sheep. Our results will provide a normative data base for ongoing gene therapy studies.

Gene Augmentation Therapy Restores Retinal Function and Visual Behavior in a Sheep Model of CNGA3 Achromatopsia

“…However, ERG recordings demonstrate that their cone function is attenuated, but not absent 19,41 . This is in contrast to ERG recordings in most human ACHM patients in which cone function is usually undetectable [51][52][53][54] to be further investigated.…”

“…The recording protocol was as detailed in Ezra-Elia et al41 . Briefly, following 10 min of light adaptation (30 cd/m 2 ), responses to four increasing intensities of stimulus (1, 2.5, 5 and 10 cd•s/m 2 ) were recorded.…”

Safety and Efficacy Evaluation of rAAV2tYF-PR1.7-hCNGA3 Vector Delivered by Subretinal Injection in CNGA3 Mutant Achromatopsia Sheep

“…1A). There was a significant increase of photopic ERGs results for both 30 Hz amplitude and critical flicker fusion frequency (CFFF) 16 for all treated groups at study weeks 6 and 12 compared to pre-dose ( p < 0.05). There was also a significant increase of photopic ERGs (both 30 Hz and CFFF) at study weeks 6 and 12 when comparing treated and untreated eyes ( p < 0.05).…”

“…16 Pupils were dilated with 0.5% tropicamide and 10% phenylephrine hydrochloride solutions ‡20 min before recording. Animals were premedicated with an intramuscular injection of acepromazine (0.1 mg/kg) and pethidine (3 mg/kg), and anesthesia was induced with an intravenous injection of propofol (4 mg/kg) and diazepam (0.15 mg/kg).…”

Retinal gene therapy: current progress and future prospects

“…This has been facilitated through structural imaging of the macula and cone cells through high-resolution spectral-domain OCT (sdOCT) [133,134] and adaptive optics in ACHM patients [135]. Although cross-sectional studies have shown variability and a lack of clear age-related disease progression [133,134], the pre-clinical successes of treatment of the canine CNGB3 -ACHM model [136], the rodent CNGA3 -ACHM model [137,138], and recent characterization of a large-animal sheep model [139] provide encouragement for potential future clinical trials.…”