Congenital multicore myopathy with external ophthalmoplegia

Multiminicore disease (MMD) is an inherited neuromuscular disorder defined pathologically by the presence of multiple areas of reduced mitochondrial oxidative activity running along a limited extent of the longitudinal axis of the muscle fiber, so-called 'minicores.' These regions show sarcomere disorganization and mitochondria depletion. Typically, no dystrophic signs, such as muscle fiber necrosis or regeneration or significant endomysial fibrosis, are present. MMD is a pathologic diagnosis and shows clinical and genetic heterogeneity. Affected individuals have clinical features of a congenital myopathy, including neonatal hypotonia, delayed motor development, and generalized muscle weakness and amyotrophy, which may progress slowly or remain stable (Ferreiro and Fardeau, 2002). Patients with recessive mutations in the RYR1 gene typically show severe congenital muscular dystrophy with ophthalmoplegia, although there is phenotypic variability. Some patients may present in utero with fetal akinesia, arthrogryposis, and lung hypoplasia resulting in fetal or perinatal death (McKie et al., 2014). Skeletal muscle biopsy of patients with recessive RYR1 mutations show variable features, including central cores (Jungbluth et al., 2007), congenital fiber-type disproportion (CFTD) (Monnier et al., 2009), and centronuclear myopathy (Wilmshurst et al., 2010).

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