"Cone dystrophy with supernormal rod electroretinogram": a comprehensive genotype/phenotype study including fundus autofluorescence and extensive electrophysiology.
OBJECTIVE
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.


CONCLUSIONS
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.
Robson
Anthony G
AG
Department of Electrophysiology, Moorfields Eye Hospital, London, UK. anthony.robson@moorfields.nhs.uk
Webster
Andrew R
AR
Michaelides
Michel
M
Downes
Susan M
SM
Cowing
Jill A
JA
Hunt
David M
DM
Moore
Anthony T
AT
Holder
Graham E
GE
D000293:Adolescent; D000328:Adult; D002648:Child; D002675:Child, Preschool; D003623:Dark Adaptation; D004594:Electrophysiology; D004596:Electroretinography; D005451:Fluorescein Angiography; D005838:Genotype; D006801:Humans; D008875:Middle Aged; D009154:Mutation; D010641:Phenotype; D010775:Photic Stimulation; D024642:Potassium Channels, Voltage-Gated / Q000235:genetics*; D017949:Retinal Cone Photoreceptor Cells / Q000473:pathology*; D012162:Retinal Degeneration / Q000175:diagnosis / Q000235:genetics / Q000503:physiopathology; D017948:Retinal Rod Photoreceptor Cells / Q000502:physiology*; D014792:Visual Acuity / Q000502:physiology; D055815:Young Adult
C489610:KCNV2 protein, human; D024642:Potassium Channels, Voltage-Gated