Dystrophinopathy muscle biopsies in the genetic testing ERA: One center's data.

Introduction: Comprehensive genetic testing for dystrophinopathy can detect ∼95% of pathogenic variants in the dystrophin gene (DMD) and is often the preferred diagnostic approach.

Methods: We reviewed pathology reports for muscle biopsies evaluated at the University of Iowa with a pathological diagnosis of dystrophinopathy based on dystrophic histopathology and abnormal immunofluorescence staining: reduced to absent dystrophin, expression of utrophin, and loss of neuronal nitric oxide synthase.

Results: The percentage of muscle biopsies with dystrophinopathy has been stable since 1997. Among 2,298 biopsies evaluated between 2011 and 2016, 72 (3.1%) had pathologic features of dystrophinopathy. Median age at biopsy was 8 years (range, 0.66-84). Half had undergone DMD genetic testing prior to biopsy. Clinical phenotypes recorded on requisitions were typical of muscular dystrophy for 57 (79%) biopsies.

Discussion: Muscle biopsy continues to play an important role in the diagnosis of dystrophinopathy, particularly in patients with later symptom onset, comorbidities, or normal DMD genetic testing results. Muscle Nerve, 2018.