Pseudodominance in two families with KCNV2 related retinopathy

PURPOSE: To describe the phenotypic and genotypic characteristics of two families with cone dystrophy with supernormal rod responses (CDSRR) presenting with a pseudodominant inheritance of disease. OBSERVATIONS: Three affected members from each family were ascertained. Family 1 of Egyptian ancestry showed consanguinity, and Family 2 was of Northern Iraqi ancestry. Both families showed pseudodominance in their pedigrees. Individuals presented with reduced visual acuity and nyctalopia. Macular disturbances were present in all, varying from a decreased foveal reflex to geographic atrophy. Electrophysiology showed reduced scotopic b-wave amplitudes and prolonged implicit times, and characteristic elevated b-wave amplitudes with high intensity flashes in all individuals. Genetic analysis of Family 1 identified a complete homozygous deletion of the KCNV2 gene, and in Family 2 a homozygous missense variation of c.562T > A: p.(Trp188Arg). CONCLUSIONS AND IMPORTANCE: To our knowledge this is the first report of pseudodominance of CDSRR, with a novel pathogenic KCNV2 variant present in the second family. Clinicians evaluating these individuals should consider autosomal recessive disease manifesting as pseudodominant inheritance. In such cases, electrophysiology remains essential for making a definitive diagnosis.