Cone dystrophy with supernormal rod responses: A rare KCNV2 gene variant.

PURPOSE

To describe the clinical, electrophysiological, and genetic findings of three Portuguese families with a rare variant in the gene resulting in "cone dystrophy with supernormal rod responses" (CDSRR).

METHODS

Retrospective clinical revision of five individuals from three unrelated families with CDSRR. Ophthalmological examination was described in all patients and included color vision testing, fundus photography, fundus autofluorescence (FAF) imaging, spectral domain-optical coherence tomography (SD-OCT), pattern electroretinogram (ERG), and full-field ERG. The mutational screening of the gene was performed with Sanger and Next Generation Sequencing.

RESULTS

All patients showed childhood-onset photophobia and progressive visual acuity loss with varying degrees of severity. In multimodal imaging, various degrees of retinal pigment epithelium disturbances and outer retinal atrophy, which tend to be worst with advancing age, were observed. Molecular screening identified a rare presumed truncating variant (p.Glu209Ter) in homozygosity in two families and in compound heterozygosity in a third family. Three patients showed ERG changes characteristic of CDSRR, however, two patients presented with incomplete electrophysiological features of the disease.

CONCLUSION

A rare variant in the gene was identified in five patients from three Portuguese families. This variant often leads to a severe and progressive form of retinopathy. Considerable variability in the ERG responses among patients with this variant was observed.