A novel MUSK mutation in a patient with CMS9

Congenital myasthenic syndromes (CMS) are a relatively rare cause of fatigable muscle weakness often with significant ocular, bulbar and respiratory impairment1. Mutations in the gene encoding muscle specific tyrosine kinase (MuSK) can lead to abnormal endplate and acetylcholine receptor functioning and cause an autosomal recessive post-synaptic CMS (CMS9). Only 23 patients with CMS9 have been characterized in the literature since the initial description in 20042.  Here, we report a newly diagnosed case of CMS9 in a 23-year-old female who harbored a novel c.296G>T (Cys99Phe) mutation in the MUSK gene, thereby expanding the phenotypic/genotypic characterization of this rare disorder.