PDE6C: Novel Mutations, Atypical Phenotype, and Differences Among Children and Adults

PURPOSE: Genetic variation in PDE6C is associated with achromatopsia and cone dystrophy, with only a few reports of cone–rod dystrophy in the literature. We describe two pediatric and two adult patients with PDE6C related cone and cone–rod dystrophy and the first longitudinal data of a pediatric patient with PDE6C-related cone dystrophy. METHODS: This cohort of four patients underwent comprehensive ophthalmologic evaluation at the National Eye Institute's Ophthalmic Genetics clinic, including visual field testing, retinal imaging and electroretinogram (ERG). Next-generation sequencing–based genetic testing was performed and subsequent analysis of the variants was done through three-dimensional protein models generated by Phyre2 and Chimera. RESULTS: All cases shared decreased best-corrected visual acuity and poor color discrimination. Three of the four patients had a cone–rod dystrophy, presenting with an ERG showing decreased amplitude on both photopic and scotopic waveforms and a mild to moderately constricted visual field. One of the children was diagnosed with cone dystrophy, having a preserved peripheral field. The children had none to minor structural retinal changes, whereas the adults had clear macular dystrophy. CONCLUSIONS: PDE6C-related cone–rod dystrophy consists of a severe phenotype characterized by early-onset nystagmus, decreased best-corrected visual acuity, poor color discrimination, progressive constriction of the visual field, and night blindness. Our work contributes with valuable information toward understanding the visual prognosis and allelic heterogeneity of PDE6C-related cone and cone–rod dystrophy.