Novel FHL1 Mutation Associated With Reducing Body Myopathy

Reducing body myopathy (RBM) is a rare X-linked myopathy caused by mutations in the FHL1 gene and characterized by intracytoplasmic aggregates that reduce menadione nitroblue tetrazolium. We report a 45-year-old female presenting with progressive proximal weakness of unknown etiology. Prior muscle biopsy and genetic testing were non-diagnostic. By repeating her muscle biopsy in a different muscle, we were able to correlate the biopsy findings with her genetic variant previously described as a variant of unknown significance. This is the first reported case of possible RBM associated with FHL1 c.401A>C (p.Gln134Pro). The case expands the genotypic spectrum of RBM and underscores the diagnostic value of repeated muscle biopsy.