As previously mentioned, considering that two recessive mutations must be present in a single individual to induce myotonia and that myotonic symptoms were referred only in patient’s mother and maternal grandmother, we hypothesize that his father could have been an asymptomatic carrier of p.G270V, whereas his mother and maternal grandmother may harbor p.G270V associated with another CLCN1 mutation. The gene discussed is CLCN1; the disease is Myotonia.