These are a group of diseases that are often familial and present in early childhood. Main features include delayed motor development, hypotonia, proximal muscle weakness, and often, facial weakness. Frequently, the disease is static or slowly progressive. Congenital myopathies are, overall, considered disturbances in myogenesis that adversely affect maturation, but without necrosis. This is a relatively mild disease that is usually dominantly-inherited.
Some patients are prone to malignant hyperthermia.
The disease is named for its most prominent feature, a central core, or well-demarcated zone in the center of the fiber that is devoid of histochemical reactivity, particularly for oxidative enzymes. EM reveals variable disruption of fiber architecture in the core. The Z bands are zigzag. Mitochondria, T-tubule and sarcoplasmic reticulum triads are absent. Central cores resemble target fibers of neurogenic disease, though targets are shorter and temporary.