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.

Signs and symptoms All 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.

Miyoshi myopathy affects the posterior muscles of the lower leg, more so than the anterior muscles of the lower leg.

Cause

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.

Types + Classic distal muscular dystrophies Type Eponym Inheritance OMIM Gene Locus Gene also implicated in: Late adult-onset type 1 Welander AD TIA1 2p13 Late adult-onset type 2a - Finnish (tibial) Udd AD TTN 2q31.2 Late adult-onset type 2b Markesbery–Griggs AD ZASP 10q23.2 Early adult-onset type 1 Nonaka AR GNE 9p13.3 Early adult-onset type 2 Miyoshi AR DYSF2p13.3-p13.1limb-girdle muscular dystrophy type 2B.Distal myopathy with anterior tibial onset (DMAT) DMAT can be considered a variant of Miyoshi. Early adult-onset type 3 Laing (Gower) AD MYH7 14q11.2 AD = autosomal dominant; AR = autosomal recessive

+ Myofibrillar myopathies classifiable as distal myopathy Type Eponym Inheritance OMIM Gene Locus Gene also implicated in: Desmin — adult onset (MFM1) Hereditary inclusion-body myositis type 1 AD αB-crystallin — early - mid adult (MFM2) AD ZASP— late adult (MFM4) AD Scapuloperoneal AD MFM = myofibrillary myopathy; AD = autosomal dominant; AR = autosomal recessive + Other distal muscular dystrophies Type Eponym Inheritance OMIM Gene Locus Gene also implicated in: Distal myopathy with vocal cord and pharyngeal weakness AD MATR3 5q31 Amyotrophic lateral sclerosis 21 (ALS21). One study suggests that all cases are ALS, justifying reclassification.

Diagnosis In 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

Management As of 2011, no disease modifying treatments are known. Foot drop can be managed with ankle-foot orthoses or surgical tendon transfer, 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. Scoliosis and contractures can be surgically managed. In 2024 a drug to treat distal myopathy was approved in Japan.

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