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| == '''Alternate names''' ==
| | #REDIRECT [[Distal myopathy]] |
| Muscular dystrophy, distal, late onset, autosomal recessive; MM; Miyoshi distal myopathy
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| == Definition ==
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| Miyoshi myopathy is a type of muscular dystrophy characterized by muscle weakness and [[atrophy]] (wasting), mainly in the distal parts of the legs.
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| == '''Epidemiology''' ==
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| The exact prevalence of Miyoshi myopathy is unknown. In Japan, where the condition was first described, it is estimated to affect 1 in 440,000 individuals.
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| == '''Cause''' ==
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| * Miyoshi myopathy is caused by pathogenic variants (mutations) in the '''DYSF gene''', which '''encodes the dysferlin protein''', a component of muscular fiber membranes.
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| * The presence and/or activity of the '''dysferlin protein is decreased or absent '''in individuals who have Miyoshi myopathy.
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| * This leads to '''abnormalities in the integrity of the muscle fiber membrane and problems with membrane repair'''.
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| * Mutations in the same gene are also involved in autosomal recessive limb-girdle muscular dystrophy type 2B (LGMD2B) and other diseases.
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| * The group of diseases caused by mutations in the '''DYSF gene''' are referred as "[[Dysferlinopathy]]".
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| == '''Inheritance''' ==
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| [[File:Autorecessive.svg|thumb|right|Autosomal recessive inheritance, a 25% chance]]
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| * Miyoshi myopathy is inherited in an [[autosomal recessive]] manner.
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| * which means both copies of the gene in each cell have mutations. The parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but they typically do not show signs and symptoms of the condition.
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| * 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.
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| == '''Signs and symptoms''' ==
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| The disease have slow progression. Onset of signs and symptoms is typically in mid to late childhood or early-adulthood, (average age at onset of 19 years), and may include:
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| * Muscle weakness and [[atrophy]] (wasting), most marked in the distal parts of the legs, especially the [[gastrocnemius]] (calf) and [[soleus]] (Achilles tendon) muscles, specially in young adults
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| * Inability to stand on tiptoe, retaining the ability to stand on the heels
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| * Slow progression of weakness and atrophy spreading to the thighs and [[Gluteal muscle|gluteal muscles]], at which time climbing stairs, standing, and walking become difficult
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| * Mildly loss of muscular mass in forearms with decrease in grip strength; the small muscles of the hands are not affected
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| * Weakness of the shoulder girdle muscles, which may occur on one side than the other.
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| == '''Clinical presentation''' ==
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| For most diseases, symptoms will vary from person to person. People with the same disease may not have all the symptoms listed.
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| '''30%-79% of people have these symptoms'''
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| * Adult onset(Symptoms begin in adulthood)
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| * Difficulty standing(Difficulty in standing)
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| * Difficulty walking(Difficulty in walking)
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| * Distal upper limb [[amyotrophy]]
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| * Exercise-induced [[myalgia]](Exercise-induced muscle pain)
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| * Pelvic girdle muscle weakness
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| * Proximal amyotrophy(Wasting of muscles near the body)
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| * [[Quadriceps]] muscle weakness(Quadriceps weakness)
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| * Shoulder girdle muscle weakness(Weak shoulder muscles)
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| * [[Tibialis]] atrophy
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| * Tibialis muscle weakness
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| '''5%-29% of people have these symptoms'''
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| * Calf muscle [[hypertrophy]](Increased size of calf muscles)
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| * Decreased/absent ankle reflexes
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| * Deposits immunoreactive to [[beta-amyloid]] protein
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| * Foot dorsiflexor weakness(Foot drop)
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| * Loss of ability to walk
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| * Toe walking(Toe-walking)
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| * [[Triceps]] weakness
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| == '''Diagnosis''' ==
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| Characteristics that may make the diagnosis of Miyoshi myopathy likely are:
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| * Mid- to late-childhood or early-adult onset of signs and symptoms
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| * Early and predominant involvement of the calf muscles
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| * Slow progression
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| * Elevation of serum [[creatine kinase]] (CK) concentration, often 10-100 times normal
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| * Primarily myogenic pattern on EMG ([[electromyography]])
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| * [[Biopsy]] evidence of a chronic, active myopathy without rimmed vacuoles
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| Diagnosis typically depends on a combination of muscle biopsy and [[genetic testing]].
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| 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).
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| Molecular [[genetic testing]] of DYSF, the only gene associated with dysferlinopathy, is clinically available.
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| == '''Treatment''' ==
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| There is currently no cure or definitive treatment for Miyoshi myopathy.
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| Management depend on the specific signs and symptoms, and is aimed to prolong survival and improve quality of life:
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| * [[Physical therapy]] and stretching exercises to promote mobility and prevent [[contracture]]s
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| * Use of mechanical aids such as [[canes]], walkers, [[Orthotic devices|orthotics]], and wheelchairs as needed to help [[ambulation]] and mobility
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| * Surgical intervention as needed for orthopedic complications such as foot deformity and scoliosis
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| * Use of respiratory aids when indicated
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| * Social and emotional support
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| * Because dysferlinopathies are progressive conditions, rehabilitative interventions should be focused on slowing down the of muscle weakness and wasting progression, rather than increasing muscle strength and walking capacity at the risk of causing irreversible muscle damage.
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| * [[Gene therapy|Gene therapies]] are under investigation.
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| {{Muscular Dystrophy}}
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| {{Diseases of myoneural junction and muscle}}
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| {{Other cell membrane protein disorders}}
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| {{musculoskeletal-disease-stub}}
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| [[Category:Muscular dystrophy]]
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| {{rarediseases}}
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| {{stub}}
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