Ophthalmologic manifestations associated with Fukutin (FKTN) variant subtypes in Korean patients with Fukuyama congenital muscular dystrophy: a single-center retrospective case series

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BACKGROUND: Fukuyama congenital muscular dystrophy (FCMD) is a severe autosomal recessive α-dystroglycanopathy caused by biallelic variants in the FKTN gene, characterized by muscular, neurological, and ocular involvement. This study aimed to evaluate the ophthalmologic manifestations associated with specific FKTN variant subtypes in Korean patients with FCMD. 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 variants comprising the RT insertion and deep intronic splice-site variants, while two patients carried non-founder variants. 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 fibrotic membranes (33.3%). Additional retinal features included dark without pressure (33.3%), tessellated fundus (33.3%), and peripheral pigmentary degeneration (44.4%). Notably, rare but vision-threatening anomalies, such as persistent fetal vasculature and tractional retinal detachment, were observed only in patients with compound heterozygous variants and were absent in those carrying non-founder variants. CONCLUSION: This study demonstrates that Korean patients with FCMD carrying compound heterozygous variants comprising the RT insertion and deep intronic splice-site variants exhibit a recognizable ophthalmic phenotype characterized by optic disc and retinal abnormalities, highlighting the need for targeted and ophthalmologic surveillance in this patient population.

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