Clinical-electroretinography mismatch in a patient with non-syndromic BBS1-associated retinal degeneration.

A male patient in his late thirties, homozygous for the M390R Bardet-Biedl Syndrome-1 (BBS1) variant, began follow-up in early adulthood, due to decreased visual acuity and photophobia. Fundus examination showed bilateral temporal wedge-shaped pallor of the optic disc and atrophic maculopathy, translating into central hypoautofluorescence on fundus autofluorescence. Even though clinical and multimodal imaging features suggested cone-dominant degeneration, electroretinography (ERG) showed reduced scotopic and photopic responses, with greater scotopic impairment. Despite a thorough systemic evaluation and long-term follow-up, no other features of BBS were found. To our knowledge, this is the first documented case of non-syndromic BBS1-associated disease with a rod-cone dystrophy phenotype on ERG and a clinical presentation (symptoms and imaging features) of cone-dominant disease. The discrepancy between clinical/imaging and ERG findings reflects the complexity of BBS1-related disease and highlights the crucial role of genetic testing and comprehensive phenotyping in inherited retinal disorders.