Clinical and Pathological Findings of Korean Patients with Selenoprotein N-Related Myopathy

Objective: This study investigated the clinical, pathological, and genetic characteristics of 5 Korean patients with selenoprotein N-related myopathy (SELENON-RM).Methods: Five unrelated patients were genetically diagnosed with SELENON-RM by whole-exome or targeted gene panel sequencing. We then analyzed their clinical, pathological, and genetic spectra.Results: The median age at symptom onset was 3 years (interquartile range, 2–10 years). The most common clinical finding was proximal muscle weakness in all 5 patients, followed by spinal scoliosis and respiratory distress in 4 patients and delayed motor development in 2 patients. Other uncommon clinical findings were winged scapula in one patient and cardiomegaly in one patient. Magnetic resonance imaging of muscles revealed that fatty replacement was predominant in the paraspinal muscles, adductors, semimembranosus, semitendinosus, long head of the biceps femoris, and medial gastrocnemius. Muscle biopsies in 2 patients showed type 1 predominance and multiple eccentric cores within the fibers. We identified 5 pathogenic variants of SELENON. The most common variant was the c.1574T > G variant in 5 alleles (50%) in 4 patients (80%).Conclusion: In the first report of SELENON-RM in Korea, we identified 5 SELENON-RM patients and expanded existing knowledge on the clinical and genetic spectrum of these patients.