Peculiar Presentation: A Case Report of Compound Heterozygous CNGA3 Pathogenic Variants in a Pediatric Patient

Background and Clinical Significance: CNGA3 variants have been implicated in congenital retinal photoreceptor disorders, especially those affecting cone photoreceptor cells and therefore color discrimination. This report details the diagnosis and unusual phenotype of a pediatric patient diagnosed with two pathogenic CNGA3 variants reported in trans. Case Presentation: A patient presented to pediatric ophthalmology at two years of age and was diagnosed with high myopia, left strabismic amblyopia, and exotropia with a binocular visual acuity of 20/1400. Amblyopia was managed with atropine 1% drops in the right eye and strabismus corrected with bilateral lateral rectus muscle recession surgery. Genetic testing revealed a compound heterozygous CNGA3 variant. An unexpectedly mild phenotype was noted with normal amplitude, slightly delayed electroretinography (ERG) responses, relatively preserved color vision with Hardy-Rand-Rittler (HRR) testing, and fundus imaging consistent with high myopia. By the age of 10, best corrected monocular visual acuity was 20/40. Conclusions: Compound heterozygous CNGA3 variants demonstrate significant variable expressivity, highlighting the need for functional testing.