Reducing body myopathy due to a novel pathogenic variant in the FHL1 gene.

A teenage girl born to non-related parents presented with progressive weakness in her lower limbs followed by her upper limbs over the past 5 years. Proximal muscle weakness was more significant than distal muscle weakness. Examination revealed weakness in both proximal and distal muscles, with an asymmetric distribution, more pronounced on the right side and in the lower limbs compared with the upper limbs. She also had mild scoliosis. Tests revealed that serum creatine phosphokinase was normal. Muscle biopsy revealed the presence of reducing bodies, as demonstrated by menadione nitro blue tetrazolium (MNBT) staining. The targeted exome sequencing identified a pathogenic missense mutation c.311G>A (p.C104Y) in the FHL1 gene. Although her clinical signs indicated muscle disease, her serum creatine phosphokinase levels were normal. Nonetheless, a muscle biopsy indicated myopathy with reducing bodies, leading to a diagnosis of FHL1-related reducing body myopathy confirmed by genetic testing.