SCN4A and periodic paralysis: The p.A1156S variant found in 1 SCM patient and the asymptomatic father (Table 2) affect the same codon of the p.A1156T mutation (LOVD: SCN4A_00044), which was reported to alter the function of Nav1.4 channel causing a channelopathy, interestingly associated with a mild phenotype without overt myotonia or periodic paralysis but with muscle pain (15).