For further information, see CMDT Part 24-36: Myopathic Disorders
Inherited myopathic disorders are subdivided by
Duchenne muscular dystrophy
Due to a genetic defect on the short arm of the X chromosome
Affected gene codes for the protein dystrophin, which is almost absent from diseased muscles
Genetic defect is detectable in pregnancy
Becker muscular dystrophy
++ Table Graphic Jump Location Table 24–10.Selected muscular dystrophies (listed in order of anatomic location and physiologic underpinning).1 ||Download (.pdf) Table 24–10. Selected muscular dystrophies (listed in order of anatomic location and physiologic underpinning).1
|Disorder ||Inheritance ||Age at Onset (years) ||Distribution ||Prognosis ||Genetic Association |
|Duchenne type ||X-linked recessive ||1–5 ||Pelvic, then shoulder girdle; later, limb and respiratory muscles. ||Rapid progression. Death within about 15 years after onset. ||Xp21; Dystrophin (loss of functional expression). |
|Becker ||X-linked recessive ||5–25 ||Pelvic, then shoulder girdle. ||Slow progression. May have normal life span. ||Xp21; Dystrophin (reduced functional expression). |
|Limb-girdle (Erb) ||Autosomal recessive, dominant, or sporadic ||10–30 ||Pelvic or shoulder girdle initially, with later spread to the other. ||Variable severity and rate of progression. Possible severe disability in middle life. ||Multiple. |
|Facioscapulohumeral ||Autosomal dominant ||Any age ||Face and shoulder girdle initially; later, pelvic girdle and legs. ||Slow progression. Minor disability. Usually normal life span. || |
4q35.2; Double homeobox protein 4.
18p11.32; Structural maintenance of chromosome’s flexible hinge domain-containing protein 1.
|Emery-Dreifuss ||X-linked recessive or autosomal dominant ||5–10 ||Humeroperoneal or scapuloperoneal. ||Variable. ||Multiple. |
|Distal ||Autosomal dominant or recessive ||40–60 ||Onset distally in extremities; proximal involvement later. ||Slow progression. ||Multiple. |
|Oculopharyngeal ||Autosomal dominant ||Any age ||Ptosis, external ophthalmoplegia, and dysphagia. ||Slow progression. ||14q11.2–q13; Poly (A)-binding protein-2. |
|Myotonic dystrophy ||Autosomal dominant ||Any age (usually 20–40) ||Face, neck, distal limbs. ||Slow progression. || |
19q13.32; Myotonin-protein kinase.
3q21.3; Cellular nucleic acid-binding protein.
Muscle weakness, often in a characteristic distribution
Age at onset and inheritance pattern depend on specific dystrophy
Pseudohypertrophy of muscles
Skeletal deformities, muscle contractures, and cardiac involvement