Congenital muscular dystrophies (CMD) are a clinically and genetically heterogeneous group of conditions, that includes a number of autosomal recessive diseases characterized by muscle weakness and possible joint deformities, present at birth and slowly progressing. Disease course for patients ranges from mild to severe although some forms of CMD might be totally asymptomatic.
The classification, based on combined clinical, genetic, and pathological data, distinguishes three main forms:
1. Disorders due to mutations in genes encoding for structural proteins of the basal lamina or extracellular matrix or receptors for extracellular matrix proteins. They include CMD variants due to mutations in the collagen 6A1, 2, and 3 genes, laminin 2 (LAMA2, one of the components of the merosin trimer), integrin 7 (ITGA7).
2. Disorders due to mutations in genes encoding for putative or demonstrated glycosyltransferases that affect the glycosylation of -dystroglycan (ADG): POMT1, POMT2, POMGnT1, FCMD, FKRP and LARGE. They include Fukuyama CMD, muscle–eye–brain disease (MEB), Walker–Warburg syndrome, MD variant 1C (MDC1C) and 1D. These are commonly referred to as secondary dystroglycanopathies.
3. Disorders related to alterations of proteins localized in the endoplasmic reticulum, which include the form with rigid spine syndrome secondary to mutations in SEPN1.