Recessive variants of MuSK are associated with late onset CMS and predominant limb girdle weakness

Am J Med Genet A. 2018 Jul;176(7):1594-1601. doi: 10.1002/ajmg.a.38707. Epub 2018 Apr 28.


Congenital myasthenic syndrome (CMS) is a heterogeneous disorder that causes fatigable muscle weakness. CMS has been associated with variants in the MuSK gene and, to date, 16 patients have been reported. MuSK-CMS patients present a different phenotypic pattern of limb girdle weakness. Here, we describe four additional patients and discuss the phenotypic and clinical relationship with those previously reported. Two novel damaging missense variants are described: c.1742T > A; p.I581N found in homozygosis, and c.1634T > C; p.L545P found in compound heterozygosis with p.R166*. The reported patients had predominant limb girdle weakness with symptom onset at 12, 17, 18, and 30 years of age, and the majority exhibited a good clinical response to Salbutamol therapy, but not to esterase inhibitors. Meta-analysis including previously reported variants revealed an increased likelihood of a severe, respiratory phenotype with null alleles. Missense variants exclusively affecting the kinase domain, but not the catalytic site, are associated with late onset. These data refine the phenotype associated with MuSK-related CMS.

Keywords: congenital myasthenic syndrome; late onset; limb girdle; muscle-specific kinase.

Publication types

  • Case Reports
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Age of Onset
  • Child
  • Female
  • Genes, Recessive*
  • Humans
  • Male
  • Muscle Weakness / genetics
  • Muscle Weakness / pathology
  • Muscular Dystrophies, Limb-Girdle / genetics*
  • Muscular Dystrophies, Limb-Girdle / pathology*
  • Mutation*
  • Myasthenic Syndromes, Congenital / genetics*
  • Myasthenic Syndromes, Congenital / pathology*
  • Prognosis
  • Receptor Protein-Tyrosine Kinases / genetics*
  • Receptors, Cholinergic / genetics*
  • Young Adult


  • Receptors, Cholinergic
  • MUSK protein, human
  • Receptor Protein-Tyrosine Kinases