Distal myopathy is a group of rare genetic disorders that cause muscle damage and weakness, predominantly in the hands and/or feet. Mutation of many different genes can be causative. Many types involve dysferlin.[1]
| Distal myopathy |
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| Other names | Distal muscular dystrophy |
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 |
| Red depicts the preferentially affected areas in distal myopathy. |
| Specialty | Neurology, neuromuscular medicine |
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| Symptoms | Weakness of hands and/or feet |
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| Complications | Cardiomyopathy |
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| Usual onset | Variable |
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| Duration | Lifetime |
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| Types | Classic, myofibrillar myopathy, other |
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| Causes | Genetic mutation of various genes |
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| Diagnostic method | Genetic testing, muscle biopsy |
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| Frequency | Rare |
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Signs and symptomsEditAll of the different types affect different regions of the extremities and can show up as early as 5 years of age to as late as 50 years old. Distal myopathy has slow progress therefore the patient may not know that they have it until they are in their late 40s or 50s.[citation needed]
Miyoshi myopathy affects the posterior muscles of the lower leg, more so than the anterior muscles of the lower leg.[2][3]
CauseEdit
DYSF
The cause of this myopathy is very hard to determine because it can be a mutation in any of at least eight genes and not all are known yet. These mutations can be inherited from one parent, autosomal dominant, or from both parents, autosomal recessive. There are eight known types of distal myopathy.[citation needed]
TypesEdit
Classic distal muscular dystrophies| Type | Eponym | Inheritance | OMIM | Gene | Locus | Gene also implicated in: |
|---|
| Late adult-onset type 1[4] | Welander | AD[5] | 604454 | TIA1[6] | 2p13[7] | |
| Late adult-onset type 2a[5] - Finnish (tibial) | Udd | AD[5] | 600334 | TTN[5] | 2q31.2 | |
| Late adult-onset type 2b[5] | Markesbery–Griggs | AD[8] | | ZASP[5] | 10q23.2 | |
| Early adult-onset type 1[4] | Nonaka | AR[5] | 605820 | GNE[5] | 9p13.3 | |
| Early adult-onset type 2[4] | Miyoshi | AR[5] | 254130 | DYSF[5] | 2p13.3-p13.1 | limb-girdle muscular dystrophy type 2B.[9] |
| Distal myopathy with anterior tibial onset (DMAT)[10][11] | | 606768 | DMAT can be considered a variant of Miyoshi. |
| Early adult-onset type 3[4] | Laing (Gower) | AD[5] | 160500 | MYH7[5] | 14q11.2 | |
| AD = autosomal dominant; AR = autosomal recessive |
Myofibrillar myopathies classifiable as distal myopathy| Type | Eponym | Inheritance | OMIM | Gene | Locus | Gene also implicated in: |
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| Desmin — adult onset (MFM1)[5] Hereditary inclusion-body myositis type 1[5] | | AD | | | | |
| αB-crystallin — early - mid adult (MFM2)[5] | | AD | | | | |
| ZASP— late adult (MFM4)[5] | | AD | | | | |
| Scapuloperoneal[5] | | AD | | | | |
| MFM = myofibrillary myopathy; AD = autosomal dominant; AR = autosomal recessive |
Other distal muscular dystrophies| Type | Eponym | Inheritance | OMIM | Gene | Locus | Gene also implicated in: |
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| Distal myopathy with vocal cord and pharyngeal weakness[4] | | AD[5] | 606070 | MATR3[5] | 5q31[5] | Amyotrophic lateral sclerosis 21 (ALS21). One study suggests that all cases are ALS, justifying reclassification.[12] |
DiagnosisEditIn terms of diagnosis, Vocal cord and pharyngeal distal myopathy should be assessed via serum CK levels, as well as muscle biopsy of the individual suspected of being afflicted with this condition[13]
ManagementEditAs of 2011, no disease modifying treatments are known.[8] Foot drop can be managed with ankle-foot orthoses or surgical tendon transfer,[8] in which the tibialis posterior muscle is repurposed to function as a tibialis anterior muscle. In select types of distal myopathy, evaluation of the heart may be indicated.[8] Scoliosis and contractures can be surgically managed.[8]