Abstract
Purpose::
To screen the recently described KCNV2 gene, encoding a voltage-gated potassium channel subunit, responsible for the cone dystrophy with supernormal rod electroretinogram, a rare retinal disorder characterized by a decrease of 30-Hz flickers cone responses while rod responses to high intensity stimuli are supernormal.
Methods::
Patients from 3 unrelated families had routine ophthalmological examination, goldman perimetry, octopus testing, funduscopy, autofluorescence imaging, OCT-3 scanning, ISCEV ERG testing and dark adaptometry. KCNV2 genomic coding sequences were PCR-amplified and subjected to direct sequencing.
Results::
All patients had a decrease in visual acuity, central scotoma and normal fundi. ERG showed highly increased implicit time (180 ms) and low amplitudes (20 µV) to the scotopic dim (25 dB) stimulus while maximum (0 dB) responses were supernormal, peaking at 650 µV. Amplitudes of 30-Hertz flickers responses were typically decreased at less than 50 µV. We found one nucleotide substitution in exon 2 (c.1381G>A) that leads to change of Glycine at codon 461 for Arginine. Glycine 461 is the third residue of the potassium selective motif (Gly-Tyr-Gly) in the P loop of the channel. Search for other mutations are currently underway.
Conclusions::
Mutation Gly461Arg is likely to disrupt the K+ selective motif in KCNV2 and therefore to cause the disease in the family.
Keywords: gene screening • retinal degenerations: hereditary • retinitis