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What are the most common limb girdle muscular dystrophy subtypes?
• LGMD 2A: Secondary to mutations in calpain, a calcium activated protease. Patients develop progressive proximal muscle weakness beginning in late childhood to adulthood. May have prominent scapular winging. CK may be mildly to severely elevated.
• LGMD 2B: Due to mutations in dysferlin, a protein involved in membrane repair. Patients develop progressive proximal muscle weakness from late childhood to adulthood, and may have normal exercise history prior to symptom onset. The same gene, and even same mutation, may also cause predominantly distal leg weakness (a.k.a. Miyoshi myopathy).
• LGMD 2C–F: Secondary to mutations in sarcoglycans, a complex of proteins involved in bridging the muscle cytoskeletal to the extracellular matrix. Severe, progressive, proximal muscle weakness usually begins in childhood. These patients may also develop cardiac and respiratory dysfunction.
• LGMD 2I: Due to mutations in Fukutin-related protein. Affected patients develop proximal weakness usually in the second decade. Patients may also develop cardiac and respiratory dysfunction. Additionally, some patients also develop scapular winging, tongue and calf hypertrophy, and cognitive dysfunction.
Sources
Bushby K, Finkel R, Birnkrant DJ et al. Diagnosis and management of Duchenne muscular dystrophy, part 1: diagnosis, and pharmacological and psychosocial management. Lancet Neurol 1:77-93, 2010.
