Congenital Muscular Dystrophies
Congenital muscular dystrophies (CMDs) comprise a group of heterogeneous disorders. Dystrophic features of the striated muscle hypotonia, muscle weakness, motor delay and symptom onset at birth or during the first months of life are the key features. Certain diseases are associated with muscle disease but also central nervous system (CNS) and eye involvement. There are many genes responsible for these diseases and an overlap exists with other hereditary myopathies including congenital myopathies ( see Chap. 15) and limb-girdle muscular dystrophies ( see Chap. 18). Together with the congenital myopathies, CMDs are the most frequent hereditary myopathies during early childhood. Their incidence has been estimated at 1/21,500 with a prevalence of 1/125,000 in Northeastern Italy and an incidence of 1/16,000 in western Sweden. However, frequency is difficult to document precisely because of the overlapping phenotypes, the lack of defined nosological frontiers, underestimation of mild forms, and geographic differences. In large cohorts of individuals with CMD, causative mutations can be identified in 25–50 % of cases. In occidental countries the most frequent forms are merosin and collagen VI deficient forms.