To review three inherited retinal disorders associated with diagnostic or pathognomonic electroretinogram (ERG) abnormalities: cone dystrophy with supernormal rod ERG (KCNV2), enhanced S-cone syndrome (NR2E3), and bradyopsia (RGS9/R9AP).
A review of clinical details, genetic basis, and electrophysiological features in these disorders and a brief summary of the standard and nonstandard ERG techniques required to identify the disorders.
The electrophysiological features in each of these three disorders are pathognomonic such that the responsible gene can be specified. The results from nonstandard electrophysiological testing in excess of international standards are necessary to describe the pathognomonic changes in cone dystrophy with supernormal rod ERG and bradyopsia. The clinical phenotype in the disorders can be variable. Mutations in NR2E3 may additionally be associated with phenotypes other than enhanced S-cone syndrome.
Characteristic ERG changes enable the diagnosis of cone dystrophy with supernormal rod ERG, enhanced S-cone syndrome, and bradyopsia and accurate genetic screening. This review highlights the need for additional nonstandard ERGs to make the diagnosis in two of these disorders.
Pathognomonic electroretinogram abnormalities, that is, changes that are specific for both a diagnosis and the responsible genetic defect, are found in only three inherited retinal disorders: “cone dystrophy with supernormal rod electroretinogram” (KCNV2), “enhanced S-cone syndrome” (NR2E3), and “bradyopsia” (RGS9/R9AP). Those disorders are reviewed.
*Department of Ophthalmology, Hospital for Sick Children, Toronto, Ontario, Canada
†Department of Electrophysiology, Moorfields Eye Hospital, London, United Kingdom
‡Institute of Ophthalmology, University College of London, London, United Kingdom.
Reprint requests: Graham E. Holder, PhD, Department of Electrophysiology, Moorfields Eye Hospital, London EC1V 2PD, United Kingdom; e-mail: email@example.com
None of the authors have any financial/conflicting interests to disclose.