Myotonic dystrophy is a genetic disease crucially characterized by myotonia (described as the difficulty in releasing musculature; typically these patients may find difficult to release the grip after shaking hands). The only known causes of myotonic dystrophy to date are either DMPK or ZNF9 repeat expansions (associated with DM1, also known as Steinert disease, and DM2 respectively).
However, in a family with some features in common with DM1 and DM2 (but also with motor neuron disease and spongiform encephalopathy), and originally thought to have DM3, a mutation in the VCP gene was detected. The family has then been defined as affected by Paget's disease and familial inclusion body myositis caused.
However, in a family with some features in common with DM1 and DM2 (but also with motor neuron disease and spongiform encephalopathy), and originally thought to have DM3, a mutation in the VCP gene was detected. The family has then been defined as affected by Paget's disease and familial inclusion body myositis caused.
The differential diagnosis of hereditary distal myopathies includes hereditary inclusion body myopathy (IBM), hereditary myofibrillar myopathy (MFM), distal muscular dystrophy (e.g. Miyoshi, Nonaka, Welander, Markesbery-Griggs), and the limb-girdle muscular dystrophies. Other hereditary disorders associated with myotonia are myotonia congenita, caused by mutations in CLCN1, paramyotonia congenita and hyperkalemic periodic paralysis its variants, caused by mutations in SCN4A (PMID: 20301344).
