A Case of PRPH2-associated Retinal Dystrophy as a Rare Cause of Electronegative ERG

A 37-year-old female presented with approximately 7 years of nyctalopia but had no central vision complaints. She was found to have a predominantly macular dystrophy with flecks and visual acuity of 20/25 in each eye. However, her full-field electroretinogram (ERG) showed an electronegative configuration (or reduced b:a ratio) under both scotopic and photopic conditions suggestive of inner retinal dysfunction of both the rod and cone systems. This phenomenon has only once been described with PRPH2-related retinopathy and the mechanism of dysfunction is particularly interesting, considering that PRPH2 is expressed in rod and cone photoreceptor outer segments, not in the photoreceptor inner segments or bipolar cells where post-phototransduction activity occurs. Thus, unknown downstream post-phototransduction effects are possible. Four paternal relatives also affected by PRPH2-retinopathy are presented, all of whom have a similar fundus appearance, though none have the electronegative ERG, highlighting the remarkable intrafamilial variability phenotype associated with pathogenic PRPH2 variants.