Improvement of Scotopic Electroretinogram (ERG) in the Setting of CNGA3 Homozygous Recessive Gene Variant

Introduction: CNGA3 is one of the most common genetic causes of autosomal recessive achromatopsia. This report describes the case of a 6-month-old patient of Mennonite background with a CNGA3 homozygous recessive gene variant presenting with an extinguished full-field electroretinogram (ffERG) consistent with an initial clinical diagnosis of Leber congenital amaurosis (LCA). However, scotopic response on repeat ffERG showed improvement with age and features consistent with the expected genetic phenotype of achromatopsia. This case highlights the need for serial ffERG for appropriate clinical prognosis and diagnosis, mainly when genetic results are inconsistent with clinical presentation. Case Presentation: A 6-month-old male patient from a Mennonite community presenting with nystagmus, intermittent eyetracking difficulty, and poor eye contact was evaluated for vision concerns. Cycloplegic refraction yielded visual acuity of +5.00D OD and +4.50D OS. Fundoscopy showed macular pigment changes, and ffERG was initially extinguished. Two subsequent ffERG at 3- and 4-year follow-ups showed non-recordable photopic ERG but scotopic ERG within expected limits. Genetic testing was significant for a pathogenic variant CNGA3 c.1126G>A, p.(Glu376Lys) in a homozygous state. Family history was significant for high myopia in his mother and achromatopsia in his maternal first cousin once removed. Management included corrective lenses and eye protection from sunlight. Conclusion: This case report describes the clinical presentation and ffERG of a Mennonite patient with a CNGA3 variant initially diagnosed with LCA, demonstrating improved scotopic ERG most consistent with achromatopsia, thus adding to our knowledge of the developmental changes in ERG in this inherited retinal disorder.