myofibrillar myopathy 9 with early respiratory failure OMIM:603689 Myofibrillar myopathy-9 with early respiratory failure (MFM9) is an autosomal dominant muscle disorder characterized by adult onset of slowly progressive muscle weakness with diaphragmatic involvement causing respiratory insufficiency. Patients present between 20 and 70 years of age with distal or proximal muscle weakness, mainly affecting the lower limbs with foot drop or difficulty walking. The age at onset is highly variable, even within families. Nearly all patients eventually develop significant proximal and distal weakness, as well as respiratory insufficiency requiring nocturnal ventilation. Additional, more variable features may include axial weakness, neck muscle weakness, and rarely, cardiac involvement. Muscle biopsy shows myopathic or dystrophic changes with fiber splitting, eosinophilic cytoplasmic inclusions consistent with myofibrillar myopathy, rimmed vacuoles, and increased connective or fatty tissue (summary by Pfeffer et al., 2014). Genetic skeletal muscle disease