“Cone Dystrophy With Supernormal Rod Electroretinogram”: A Comprehensive Genotype/Phenotype Study Including Fundus Autofluorescence and Extensive Electrophysiology

In Brief Purpose: The purpose of this study was to characterize the clinical, electrophysiologic, and genetic features in “cone dystrophy with supernormal rod electroretinogram (ERG).” Methods: Twenty-four cases between 5 and 59 years of age were ascertained. Full-field ERGs, incorporating the international standards, were used to derive intensity-ERG response functions. ON-OFF ERGs were performed. Fundus autofluorescence imaging was performed on 15 subjects. Deoxyribonucleic acid was available in 18 cases and was screened for a mutation in KCNV2. Results: Photophobia and nyctalopia were common. Autofluorescence was variable but often showed a ring-like area of high density that in middle-aged individuals, usually surrounded by an area of macular retinal pigment epithelial atrophy. Scotopic ERG amplitudes overlapped with the normal range but had characteristic a- and b-wave intensity-response functions; all had a broadened a-wave to the brightest flash. Photopic ERGs were abnormal; there was a delay in some ON and most OFF responses. Mutations in KCNV2 were detected in 18 cases, including 4 with novel mutations. Conclusion: Individuals with mutations in KCNV2 manifest a wide range of macular and autofluorescence abnormalities. A ring-like area of parafoveal high density autofluorescence is common. ERG amplitudes are variable, but the intensity-ERG response functions and bright flash ERG waveforms are pathognomonic. The clinical, genetic, and electrophysiologic features of 24 patients with “cone dystrophy and supernormal rod electroretinogram” are described. Comprehensive and novel fundus autofluorescence imaging data are presented, and the ranges of electroretinogram intensity-response functions are quantified. Novel mutations in KCNV2 are identified.