[Selenoprotein-related myopathy in a patient with old-age-onset type 2 respiratory failure: a case report]

[SELENON-related myopathy with scoliosis and respiratory failure since early childhood diagnosed through reassessment during pediatric-to-adult healthcare transition: a case report]

The patient was a 33-year-old woman with no family history of a similar disorder. At one year of age, she exhibited scoliosis and respiratory failure, necessitating a tracheostomy performed at 5 years of age (1990s). During that time, the patient was provisionally diagnosed with "non-Fukuyama congenital muscular dystrophy" via muscle biopsy. Difficulties in independent walking and standing emerged by 14 years of age, progressing to significant mobility challenges by 21 years of age. The patient was referred to our department at 33 years of age for the transition to adult care. The examination revealed predominant trunk muscle weakness, persistent scoliosis, restricted neck and trunk mobility, significant restrictive ventilatory impairment, and mild intellectual developmental delay. Reanalysis of the muscle biopsy pathology was conducted, and genetic testing identified a known homozygous mutation, c.1574T>G (p.M525R), in the SELENON (SEPN1) gene, leading to a diagnosis of SELENON-related myopathy. The pediatric-to-adult healthcare transition can provide a valuable opportunity for the reassessment of diagnoses and disabilities.

Delayed Respiratory Insufficiency and Extramuscular Abnormalities in Selenoprotein N-Related Myopathies

Background: Selenoprotein N-related myopathies (SEPN1-RMs) are a subset of congenital myopathies caused by mutations of Selenoprotein N gene (SELENON or SEPN1). Clinical phenotype is considered as highly consistent and little attention has been given to the extramuscular abnormalities. Methods: We reported clinical, histopathological, and genetic features of four Chinese patients with SEPN1-RM and performed literature review on delayed respiratory insufficiency and extramuscular involvement. Results: A total of four patients exhibited both the typical and atypical clinical features of SEPN1-RM. The classical manifestations included axial and limb girdle weakness, spinal rigidity, scoliosis, respiratory insufficiency, and multiminicore morphological lesions. However, high interindividual variability was noticed on disease severity, especially the onset of respiratory involvement. Two adult patients postponed respiratory insufficiency to the third decade of life, while two juvenile patients manifested early hypoventilation with puberty exacerbation. As atypical features, extramuscular involvement of weight gain, subcutaneous adipose tissue accumulation, intellectual disability, and mild cardiac changes were observed. Molecular findings revealed three novel mutations of SELENON such as c.1286_1288 del CCT, c.1078_1086dupGGCTACATA, and c.785 G>C. Ten cases with delayed respiratory insufficiency were identified from previous publications. A total of 18 studies described extramuscular abnormalities including joint contractures, alterations of body mass index (BMI), mild cardiac changes, and insulin resistance. Intellectual impairment was extremely rare. Conclusion: SEPN1-RM should be considered as a differential diagnosis in adult patients with delayed respiratory involvement. Extramuscular involvement such as body composition alterations deserves more clinical attention. The novel mutations of SELENON widened the genetic spectrum of patients with SEPN1-RM.