Congenital Myopathy 1B, Autosomal Recessive

Alternative Names

  • CMYP1b
  • Minicore Myopathy with External Ophthalmoplegia
  • Minicore Myopathy
  • Multicore Myopathy
  • Multiminicore Myopathy
  • Multicore Myopathy with External Ophthalmoplegia
  • Multiminicore Disease with External Ophthalmoplegia

Associated Genes

Ryanodine Receptor 1
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WHO-ICD-10 version:2010

Diseases of the nervous system

Diseases of myoneural junction and muscle

OMIM Number


Mode of Inheritance

Autosomal recessive

Gene Map Locus



Congenital myopathy-1B (CMYP1B) is an autosomal recessive disorder of skeletal muscle characterized by severe hypotonia and generalized muscle weakness apparent soon after birth or in early childhood with delayed motor development, generalized muscle weakness and atrophy, and difficulty walking or running. Affected individuals show proximal muscle weakness with axial and shoulder girdle involvement, external ophthalmoplegia, and bulbar weakness, often resulting in feeding difficulties and respiratory insufficiency. Orthopedic complications such as joint laxity, distal contractures, hip dislocation, cleft palate, and scoliosis are commonly observed. Serum creatine kinase is normal. The phenotype is variable in severity. Some patients show symptoms in utero, including reduced fetal movements, polyhydramnios, and intrauterine growth restriction. The most severely affected patients present in utero with fetal akinesia, arthrogryposis, and lung hypoplasia resulting in fetal or perinatal death. Skeletal muscle biopsy of patients with recessive RYR1 mutations can show variable features, including multiminicores, central cores, congenital fiber-type disproportion (CFTD), and centronuclear myopathy. [From OMIM]

Epidemiology in the Arab World

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Subject IDCountrySexFamily HistoryParental ConsanguinityHPO TermsVariantZygosityMode of InheritanceReferenceRemarks
255320.1Saudi ArabiaUnknownYesYes Ptosis; Aplasia/Hypoplasia of the sacrumNM_000540.3:c.6617C>THomozygousAutosomal, RecessiveAlazami et al. 2015 No motor delay
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