Definition:

Multi-minicore Disease (MmD) is a recessively inherited neuromuscular disorder characterized by multiple cores on muscle biopsy and clinical features of a congenital myopathy. It is morphologically defined by localized multiple areas of mitochondrial depletion and sarcomere disorganization, running to a limited extent along the longitudinal axis of muscle fiber ("minicores"). Marked clinical variability corresponds to genetic heterogeneity. Mutations in the SEPN1 gene have been identified in patients with the classic axial phenotype characterized by spinal rigidity, early scoliosis, and respiratory impairment, whereas mutations in the RYR1 gene have been associated with a wider range of clinical features comprising external ophthalmoplegia, distal weakness and wasting or predominant hip girdle involvement.