Although several CMS subtypes such as slow-channel syndrome (Chaouch et al., 2012), DOK7-CMS (Müller et al., 2007) and GFPT1-CMS (Guergueltcheva et al., 2011) can have mildly raised creatine kinase values, this is rare (apart from in GFPT1-CMS, not seen in over 300 CMS cases analysed in Oxford), and when reported has rarely been more than two to three times normal values. Here, GFPT1 is linked to congenital myasthenic syndrome.