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Genetic and Rare Diseases Information Center (GARD)

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Miyoshi myopathy


Other Names for this Disease
  • Miyoshi distal myopathy
  • MM
  • Muscular dystrophy, distal, late onset, autosomal recessive
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Overview



What is Miyoshi myopathy?

What are the signs and symptoms of Miyoshi myopathy?

What causes Miyoshi myopathy?

How is Miyoshi myopathy inherited?

Is genetic testing available for Miyoshi myopathy?

How is Miyoshi myopathy diagnosed?

How might Miyoshi myopathy be treated?


What is Miyoshi myopathy?

Miyoshi myopathy is a type of muscular dystrophy characterized by muscle weakness and atrophy (wasting), mainly in the distal parts of the legs.[1] The first symptoms typically begin in young adulthood (on average 20 years of age) and include weakness and atrophy of the calves (sometimes asymmetrically), leading to inability to jump, run or walk on tiptoes. Over a period of years, the weakness and atrophy typically spread to the thighs and gluteal muscles. The forearms may become mildly atrophic with decrease in grip strength.[1] It is caused by mutations in the DYSF gene and is inherited in an autosomal recessive manner.[2] Management may include physical therapy, use of mechanical aids, surgical intervention for orthopedic complications, respiratory aids, and social and emotional support.[1]
Last updated: 4/5/2011

What are the signs and symptoms of Miyoshi myopathy?

The onset of signs and symptoms is typically in mid to late childhood or early-adulthood, with an average age at onset of 19 years. Young adults typically have muscle weakness and atrophy (wasting), most marked in the distal parts of the legs, especially the gastrocnemius (calf) and soleus (Achilles tendon) muscles. Early on, affected individuals are not able to stand on tiptoe, but retain the ability to stand on the heels. Over a period of years, the weakness and atrophy spread to the thighs and gluteal muscles, at which time climbing stairs, standing, and walking become difficult. The forearms may become mildly atrophic with decrease in grip strength; the small muscles of the hands are not affected. The weakness may eventually include the shoulder girdle muscles. The weakness and atrophy may be asymmetric (occurring more on one side than the other). Progression of the condition is typically slow.[1]
Last updated: 4/5/2011

What causes Miyoshi myopathy?

Miyoshi myopathy is caused by mutations in the DYSF gene, which encodes the dysferlin protein, a component of muscular fiber membranes. The presence and/or activity of the dysferlin protein is decreased or absent in individuals who have Miyoshi myopathy.[2] This leads to abnormalities in the integrity of the muscle fiber membrane and problems with membrane repair. Mutations in the same gene are also involved in autosomal recessive limb-girdle muscular dystrophy type 2B (LGMD2B).
Last updated: 4/5/2011

How is Miyoshi myopathy inherited?

Miyoshi myopathy is inherited in an autosomal recessive manner.[1] Individuals have two copies of each gene (one copy inherited from each parent). In an individual affected with an autosomal recessive condition, both copies of the responsible gene have mutations. This means that each of the parents of an affected individual carry one mutated copy of the gene, and are therefore referred to as "carriers." Carriers of an autosomal recessive condition typically do not show signs or symptoms of the condition. When two carriers for the same condition have children together, each child has a 1 in 4 (25%) risk to have the condition, a 1 in 2 (50%) risk to be a carrier like each of the parents, and a 1 in 4 chance to not have the condition and not be a carrier. Carrier testing for at-risk relatives and prenatal diagnosis for pregnancies at increased risk are possible if the disease-causing mutations in the family are known.
Last updated: 6/6/2011

Is genetic testing available for Miyoshi myopathy?

Yes, genetic testing for this condition is available. GeneTests lists the names of laboratories that are performing genetic testing for Miyoshi myopathy. To view the contact information for the clinical laboratories conducting testing, click here. To access the contact information for the research laboratories performing genetic testing, click here.

Please note: Most of the laboratories listed through GeneTests do not accept direct contact from patients and their families; therefore, if you are interested in learning more, you will need to work with a health care provider or a genetics professional.
Last updated: 4/5/2011

How is Miyoshi myopathy diagnosed?

Characteristics that may make the diagnosis of Miyoshi myopathy likely are:
  • Mid- to late-childhood or early-adult onset of signs and symptoms
  • Early and predominant involvement of the calf muscles
  • Slow progression
  • Elevation of serum creatine kinase (CK) concentration, often 10-100 times normal
  • Primarily myogenic pattern on EMG (electromyography)
  • Biopsy evidence of a chronic, active myopathy without rimmed vacuoles[1]
Diagnosis typically depends on a combination of muscle biopsy and genetic testing. Muscle biopsy almost always indicates a primary dysferlinopathy (a disorder involving dysferlin, the protein absent or decreased in individuals with Miyoshi myopathy and limb-girdle muscular dystrophy type 2B). Molecular genetic testing of DYSF, the only gene associated with dysferlinopathy, is clinically available.[1]
Last updated: 6/6/2011

How might Miyoshi myopathy be treated?

There is currently no cure or definitive treatment for Miyoshi myopathy. Management should be tailored to each individual, depending on his/her specific signs and symptoms. A general approach to appropriate management can prolong survival and improve quality of life.[1] This approach may include:
  • Physical therapy and stretching exercises to promote mobility and prevent contractures
  • Use of mechanical aids such as canes, walkers, orthotics, and wheelchairs as needed to help ambulation and mobility
  • Surgical intervention as needed for orthopedic complications such as foot deformity and scoliosis
  • Use of respiratory aids when indicated
  • Social and emotional support and stimulation to maximize a sense of social involvement and productivity and to reduce the sense of social isolation common in these disorder[1]
Last updated: 4/5/2011

References
  1. Masashi Aoki. Dysferlinopathy. GeneReviews. April 22, 2010; http://www.ncbi.nlm.nih.gov/books/NBK1303/. Accessed 4/4/2011.
  2. I. Pénisson-Besnier. Miyoshi myopathy. Orphanet. April 2004; http://www.orpha.net/consor/cgi-bin/OC_Exp.php?lng=EN&Expert=45448. Accessed 4/4/2011.