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

: 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 gene, which encodes a subunit (Kv8.2) of the voltage-gated potassium channel. : The genetic testing of two patients included the next-generation sequencing of a retinal dystrophy panel and direct Sanger sequencing to confirm gene variants, in addition to an electroretinogram (ERG) and spectral domain optical coherence tomography (SD-OCT). : Cone dystrophy with supernormal rod response is associated with identified variants in the gene. The genetic analysis of the first case identified a compound heterozygous mutation in the 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 mutation database, added an unreported de novo substitution pattern to gene variants, and linked it to the evaluated clinical studies. : The initial clinical manifestations were varied, but both patients presented with hypermetropia and slight exotropia. The ERG findings are characteristic of mutations, and patients exhibited an increased b-wave latency in DA3.0 ERG (combined rod-cone response).