Atypical Retinitis Pigmentosa With Macular Sparing in a Patient With Compound Heterozygous <i>ABCA4</i> Variants: A Case Report and Diagnostic Challenge

Inherited retinal dystrophies are a complex group of disorders causing progressive vision loss. The <i>ABCA4</i> gene is associated with a wide spectrum of retinopathies, most commonly Stargardt disease, which is characterized by central macular degeneration. Retinitis Pigmentosa (RP) is a less common but recognized <i>ABCA4</i>-associated phenotype, typically involving severe, pan-retinal degeneration. A 25-year-old male presented with a 5-year history of nyctalopia and progressive peripheral visual field loss. Best-corrected visual acuity was 1/20 in the right eye and 20/20 in the left eye. Fundus examination revealed pale optic discs, attenuated retinal arteries, and peripheral bone spicule-like pigment deposits, with notable sparing of the macula. Genetic analysis identified compound heterozygous variants in the <i>ABCA4</i> gene: a known pathogenic variant, c.4793C>A (p.Ala1598Asp), inherited from his father, and a novel variant, c.1769A>G (p.Asp590Gly), inherited from his mother. The novel variant was re-evaluated according to ACMG/AMP guidelines and classified as likely pathogenic based on its absence in population databases, co-segregation with disease, and high <i>in silico</i> prediction scores. This case presents a diagnostic challenge, with a clinical phenotype of macular sparing RP and strong genetic evidence implicating <i>ABCA4</i>. These findings expand the potential phenotypic spectrum of <i>ABCA4</i>-retinopathy and underscore the critical role of genetic testing in diagnosing patients with atypical presentations of inherited retinal disease. Further investigation is needed to fully elucidate the pathogenic mechanism of the novel variant and its contribution to this unusual clinical picture.