Presently, about 40 mutations in the Rapsn gene have been identified in patients with CMSs, accounting for 15% of total CMS cases (Dunne and Maselli, 2003; Maselli et al., 2007; Maselli et al., 2003; Milone et al., 2009; Müller et al., 2004; Ohno and Engel, 2004; Ohno et al., 2002; Ohno et al., 2003; Yasaki et al., 2004). Here, RAPSN is linked to congenital myasthenic syndrome.