Short-term response to phenytoin sodium in Andersen-Tawil syndrome-1 with a cardiac-dominant phenotype

Background: Andersen-Tawil syndrome (ATS) is a rare familial periodic paralysis that typically also affects the heart and skeletal system. Ventricular arrhythmias (VAs) are profound and difficult to control, but minimally symptomatic. In this report, we describe an atypical phenotype of ATS in two related families. We also report our experience with phenytoin sodium for the control of resistant VAs in these patients. Methods and Results: Between 2014 and 2018, seven siblings were diagnosed with ATS on the basis of cardiac arrhythmias and genetic evaluation. Heterozygous mutation with c.431G > C (p.G144A) in exon 2 of KCNJ2 gene was observed in all patients. Characteristic cardiac manifestations were noted in all patients but periodic paralysis or objective neurological involvement was distinctly absent. Phenytoin was considered for control of symptomatic VA in three patients. Intake of oral phenytoin (5 mg/kg/day) for 1 month completely suppressed VA (<1% in 24-h Holter monitoring) in two patients, and significantly in the third (8% per 24 h) patient. Phenytoin was well-tolerated in all three patients. Conclusions: We describe a cardiac-predominant phenotype in ATS. ATS should be suspected in patients with typical cardiac manifestations even in the absence of periodic paralysis. Our initial experience with short-term use of phenytoin for control of resistant VAs is encouraging.