Congenital muscular dystrophy (CMD) is a general term for a group of genetic muscle diseases that occur at birth (congenital) or early during infancy. CMDs are generally characterized by diminished muscle tone (hypotonia), which is sometimes referred to as "floppy baby"; progressive muscle weakness and degeneration (atrophy); abnormally fixed joints that occur when thickening and shortening of tissue such as muscle fibers cause deformity and restrict the movement of an affected area (contractures); spinal rigidity, and delays in reaching motor milestones such as sitting or standing unassisted. Feeding difficulties and breathing (respiratory) complications can develop in some cases. Muscle weakness may improve, remain stable or worsen. Some forms of CMD may be associated with structural brain defects and, potentially, intellectual disability. The severity, specific symptoms, and progression of these disorders vary greatly. Most forms of CMD are inherited as autosomal recessive traits. Collage type VI-related disorders can be inherited as either autosomal dominant or autosomal recessive conditions. LMNA-related CMD is inherited in an autosomal dominant manner, with all mutations reported to date being new mutations (de novo).
CMDs belong to a larger group of disorders known as the muscular dystrophies. The muscular dystrophies characterized by weakness and degeneration of various voluntary muscles of the body. More than 30 different disorders make up the muscular dystrophies. The disorders affect different muscles and have different ages of onset, severity and inheritance patterns. As researchers have learned more about the CMDs, such as identifying many of the specific genes involved, a broader picture of these diseases has emerged. The subtypes of CMD have considerable overlap with other disease classifications including the congenital myopathies, disorders of glycosylation, and the limb-girdle muscular dystrophies. CMDs are a rapidly growing disease family and information about these disorders is constantly changing.