Electroretinogram alterations in a monozygotic twin sisters discordant retinitis pigmentosa

Abstract Purpose We describe the electroretinographic alteration in an interesting and unusual case of a twin sisters discordant Retinitis Pigmentosa (RP). Methods A 30‐year‐old woman complained of night blindness. She and her twin sister, underwent complete ophthalmological exams including fundoscopy, retinography and electroretinogram at the Clinical Hospital of the University of São Paulo. Results The scotopic full‐field electroretinogram was non detectable and not significantly different from noise. The fotopic and flicker responses were present, but abnormal. The multifocal electroretinogram (mfERG) showed a residual central cone response. The scotopic and fotopic full‐field electroretinogram and mf‐ERG of the sister were normal. Conclusion The discordant RP is very rare and the electrophysiological tests are important to confirm diagnosis. We believe that RP can manifest in incomplete penetrance or in different phenotypes.