Congenital myopathies primarily affect skeletal muscle fibres with a heterogeneous clinical and genetic picture. The diseases are due to genetic mutation of various muscle proteins and the classification is based on specific abnormalities in muscle proteins and on abnormalities found in muscle biopsies.
This set of muscle disorders usually appears at birth or in infancy, with muscle weakness in axial and proximal distribution (i.e. muscles close to the median plane). Muscle weakness is often relentless, and diaphragm weakness and respiratory insufficiency may be severe.
Patients with congenital myopathy usually show a typical facial appearance (myopathic facies) consisting of weakness of facial muscles and dysmorphisms, osteoarticular malformations (e.g. retractions, scoliosis, spinal rigidity) and ligamentous laxity (e.g. loose ligaments).
Structural alterations in CNS and PNS are usually absent. Cognition is usually unimpaired. Most common types of congenital myopathy are Central Core disease, Nemaline myopathy, Centronuclear myopathy, Multi-minicore disease, and Myofibrillar myopathy.
Incidence of each type is unclear: the whole set of myopathies represents 14% of Congenital Hypotonia.