A new clinical entity in T704M mutation in periodic paralysis

•Different SCN4A gene mutations cause different types of paralysis syndromes.•First family reported that inherits the T704M mutation with a HypoKPP clinic.•Unusual symptoms during the period of the attacks, diplopia and bad smelling in periodic paralysis patients.•We still need to improve genotype-phenotype correlation in T704M mutation.•T704M mutation, showes interfamilial and intrafamilial clinical variability.