Compound heterozygous KCNV2 variants contribute to cone dystrophy with supernormal rod responses in a Chinese family

Novel and Previously Known Mutations of the KCNV2 Gene Cause Various Variants of the Clinical Course of Cone Dystrophy with Supernormal Rod Response in Children

Background/Objectives: Cone dystrophy with supernormal rod response (CDSRR) is a rare autosomal recessive retinal disorder characterized by a delayed and markedly decreased photoreceptor response. In this article, we aim to describe the clinical course and associated molecular findings in children with cone dystrophy with supernormal rod response associated with recessive mutations in the KCNV2 gene, which encodes a subunit (Kv8.2) of the voltage-gated potassium channel. Methods: The genetic testing of two patients included the next-generation sequencing of a retinal dystrophy panel and direct Sanger sequencing to confirm KCNV2 gene variants, in addition to an electroretinogram (ERG) and spectral domain optical coherence tomography (SD-OCT). Results: Cone dystrophy with supernormal rod response is associated with identified variants in the KCNV2 gene. The genetic analysis of the first case identified a compound heterozygous mutation in the KCNV2 gene, including a de novo nonsense duplication at cDNA position 1109, which led to the premature termination of the p.Lys371Ter codon in the second extracellular domain of the protein. Two patients showed changes in the full-field electroretinogram, especially in the first case, which demonstrated a close to supernormal total electroretinogram amplitude. This study increased the range of the KCNV2 mutation database, added an unreported de novo substitution pattern to KCNV2 gene variants, and linked it to the evaluated clinical studies. Conclusions: The initial clinical manifestations were varied, but both patients presented with hypermetropia and slight exotropia. The ERG findings are characteristic of KCNV2 mutations, and patients exhibited an increased b-wave latency in DA3.0 ERG (combined rod-cone response).

Compound heterozygous KCNV2 variants contribute to cone dystrophy with supernormal rod responses in a Chinese family

Background

Cone dystrophy with supernormal rod response (CDSRR) is an autosomal recessive retinal disorder characterized by myopia, dyschromatopsia, nyctalopia, photophobia, and nystagmus. CDSRR is caused by mutations in KCNV2, the gene encoding for an electrically silent Kv subunit (Kvs) named Kv8.2.

Methods

A Chinese CDSRR family was recruited. Complete ophthalmology clinical examinations were performed to clarify the phenotype. Genetic examination was underwent using whole exome sequencing (WES). In addition, a candidate gene was validated by Sanger sequencing. Expression analysis in vitro including immunoblotting, quantitative real‐time PCR (qRT‐PCR), and co‐immunoprecipitation experiments was performed to investigate the pathogenic mechanism of the identified gene variants.

Results

WES identified two KCNV2 heterozygous mutations from the proband. Sanger sequencing validated that the patient's parents had, respectively, carried those two mutations. Further in vitro functional experiments indicated that the mutated alleles had led the Kv8.2 proteins to fail in expressing and interacting with the Kv2.1 protein, respectively.

Conclusions

This study expanded the KCNV2 mutation spectrum. It can also be deduced that CDSRR has a broad heterogeneity. It is further confirmed that the inability expression of Kv8.2 proteins and the failure of Kv8.2 proteins to interact with Kv2.1 may have accounted for the etiology of CDSRR based on previous studies and this study.