Ophthalmologic Manifestations Associated with Fukutin (FKTN) mutation subtypes in Korean Patients with Fukuyama Congenital Muscular Dystrophy: A Single-Center Retrospective Case Series

Background To evaluate phenotypes in Korean patients with Fukuyama congenital muscular dystrophy (FCMD), with a particular focus on ocular manifestations associated with specific Fukutin ( FKTN ) mutation subtypes. Methods We conducted a retrospective review of nine patients with genetically confirmed FCMD who were followed at a single tertiary referral center between 2005 and 2024. Comprehensive ophthalmologic evaluations were correlated with molecular genotyping, including detection of founder retrotransposon (RT) insertions and splice-disrupting variants in the FKTN gene. Results Seven of nine patients (77.8%) harbored compound heterozygous mutations comprising the RT insertion and deep intronic splice-site variants, while two patients carried non-founder mutations. The mean age at last ophthalmic evaluation was 7.59 ± 4.74 years. High myopia (44.4%), strabismus (22.2%), and nystagmus (11.1%) were frequently observed. Fundus examination revealed optic disc abnormalities in 77.8% of patients, including small discs (55.6%), pale discs (33.3%), and peripapillary fibrovascular membranes (33.3%). Additional retinal features included pigment without pressure (33.3%), tigroid fundus (33.3%), and peripheral retinal pigmentation (44.4%). Notably, rare but vision-threatening anomalies such as persistent fetal vasculature, and tractional retinal detachment were exclusively detected in patients with compound heterozygous mutations. Conclusion This study reveals a distinct ophthalmic phenotype in Korean patients with FCMD, characterized by optic nerve and retinal abnormalities. These findings suggest that patients with these genotypes may benefit from targeted and proactive ophthalmologic surveillance. Further studies in larger cohorts are warranted to validate these genotype-specific correlations.