Clinical Validation of a CRX Variant Leading to a Cone-Rod Dystrophy

Patients with cone-rod dystrophy (CORD) due to CRX mutations have progressive visual impairment characterized by central vision loss, photophobia, and color vision defects. On ophthalmic examination, patients with CRX-associated CORD may have macular abnormalities, changes in the retinal pigment epithelium, and progressive macular degeneration, affecting central visual function. Variants in the CRX gene located on chromosome 19q13 lead to photoreceptor dysfunction and retinal degeneration. Variant classification in CRX presents unique challenges, as approximately half of heterozygous missense variants may be benign, requiring careful phenotype-genotype correlation for accurate pathogenicity determination. Our patient had progressive vision loss, bilateral macular abnormalities, and visual symptoms compatible with CORD. The patient's clinical findings included central visual field defects, reduced multifocal electroretinography responses, and preserved full-field electroretinography consistent with macular-restricted disease. Next-generation sequencing showed a heterozygous, likely pathogenic variant c.166G>A (p.Ala56Thr) located within the homeodomain at residue 56. Comprehensive ophthalmic examination, electrophysiological testing, and genetic studies may all help reach a CORD diagnosis. This case highlights the importance of phenotype-driven variant interpretation for reclassifying CRX variants from "likely pathogenic" to "pathogenic" and raises clinical awareness for the critical role of genotype-phenotype concordance in inherited retinal dystrophies.