FHL1-related myopathy may not be classified by reducing bodies in muscle biopsy

Abstract

FHL1-related myopathies, including reducing body myopathy (RBM), X-linked scapulo-axio-peroneal myopathy, rigid spine syndrome, X-linked myopathy with postural muscle atrophy (XMPMA), X-linked Emery-Dreifuss muscular dystrophy and hypertrophic cardiomyopathy, are clinically and pathologically heterogeneous disorders caused by FHL1 gene mutations. According to previous reports, the first three types are myopathies with reducing bodies observed in biopsies, and the last three are myopathies without reducing bodies. We report four FHL1-related myopathy patients, including an XMPMA patient and a RBM family with three patients. Clinical information, muscle biopsies, electromyograms and genetic testing were obtained. Muscle weakness and atrophy, spinal rigidity, and joint contracture were present in the RBM family. The XMPMA patient showed a pseudoathletic appearance with muscle weakness and atrophy, spinal rigidity and deformity. The index patient of the RBM family underwent two muscle biopsies to find reducing bodies. Interestingly, these muscle biopsies revealed reducing bodies and rimmed vacuoles not only in the RBM family but also in the XMPMA patient. Next-generation sequencing identified a reported single missense mutation c.448 C>T (p. C150R) in the RBM family and a novel mutation c.814T>C (p. S272P) in the XMPMA patient. Therefore, FHL1-related myopathies overlap substantially and may not be simply classified into subtypes depending on reducing bodies. Biopsies of additional affected muscles can aid in finding reducing bodies. We report the first XMPMA patient with a novel FHL1 mutation and reducing bodies in a muscle biopsy in China.

Keywords: FHL1; Muscle biopsy; Novel mutation; Reducing body myopathy; X-linked myopathy with postural muscle atrophy.