Exclusively Macular Phenotype of Non-Syndromic MFSD8-Related Disease: A Case Report.

Introduction: The purpose of this report was to highlight the clinical phenotype and imaging findings in a patient with an exclusively macular phenotype of non-syndromic MFSD8-related disease and to provide clinical evidence for pathogenicity reclassification of a variant of uncertain significance MFSD8 c.291G>C (p.Trp97Cys).

Case presentation: A 47-year-old male with progressive vision loss exhibited symptoms indicative of maculopathy. These included decreased central vision, visual distortions, photophobia, poor depth perception, glare, impaired dark/light adaptation, difficulty reading, depressed multifocal ERG responses, and central ellipsoid dropout on SD-OCT. Evaluation included genetic testing, segregation analysis, and a complete ophthalmic examination, including slit-lamp exam, dilated fundus exam, FAF, SD-OCT, ERG, and Humphrey 24-2 visual fields. A 351 gene retinal dystrophy panel revealed two variants in MFSD8, including one pathogenic variant (c.1006G>C, p.Glu336Gln) and one likely pathogenic variant (c.291G>C, p.Trp97Cys), confirmed to be in trans via segregation testing.

Conclusion: This case underscores the importance of genetic testing in confirming variant inheritance and describes the clinical phenotype associated with MFSD8 c.291G>C (p.Trp97Cys). The variant contributes to a pathological non-syndromic phenotype when in trans with a pathogenic variant. Given the syndromic variants of MFSD8, patients with this specific variant in the homozygous or compound heterozygous state should be closely monitored for clinical manifestations associated with this condition. Genetic counseling should be recommended for affected individuals and their close relatives to provide informed guidance regarding prognosis, reproductive risks, and available support resources.