This information is provided by the National Institutes of Health (NIH) Genetic and Rare Diseases Information Center (GARD).
The congenital muscle dystrophies are currently classified according to the genetic defects. Historically, congenital muscular dystrophies were classified in two broad groups: Classic CMD (which included the Merosin-deficient CMD and the Merosin-positive CMD)
and the CMD with central nervous system (CNS) abnormalities (Fukuyama CMD, muscle-eye-brain disease and Walker-Warburg syndrome).
Therefore, merosin-positive congenital muscle dystrophy (CMD) is now considered an old term which refers to a group of diseases without structural brain abnormalities that are caused by a variety of gene mutations, resulting in protein defects that do not affect the merosin protein. It usually has a milder phenotype than the merosin-negative CMD dystrophy group and includes, among others:
Classic CMD without distinguishing features
Rigid spine syndrome associated with mutations in the selenoprotein N1 gene (SEPN1)
CMD with hyperextensible distal joints (Ullrich type)
CMD with intellectual disability or sensory abnormalities.
The pattern of muscle weakness and wasting in the patients within this group of congenital muscular dystrophy conditions is worse in the proximal upper limb-girdle and trunk muscles. Lower limb muscles may be mildly involved. Muscle biopsy shows a dystrophic pattern with normal staining for dystrophin, laminin alpha-2 of merosin and the sarcoglycans.
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