Andersen-Tawil syndrome includes a clinical triad consisting of periodic 
paralysis, cardiac arrhythmia, and usually mild but diagnostically useful 
dysmorphic features. This potassium channelopathy is due to mutation of the 
KCNJ2 gene encoding the protein Kir 2.1. The main muscular manifestation is 
periodic paralysis, usually of the hypokalemic type. Muscle biopsy may reveal 
tubular aggregates or be normal, as in our patient. Cardiac manifestations are 
variable and may include a long QT syndrome, premature ventricular contractions, 
complex ventricular ectopy, and polymorphic or bidirectional ventricular 
tachycardia. Imipramine therapy had a positive effect on arrhythmia in our 
patient. Dysmorphic features provide a diagnostic clue but may be difficult to 
identify and should thus be methodically sought. Clinical expression is 
variable, even within the same family. Since the culprit gene KCNJ2 was 
identified, locus heterogeneity has been shown in Andersen-Tawil syndrome. 
Kindreds without KCNJ2 mutations are clinically indistinguishable from those 
with mutations. Kir2.1 is an inward rectifier K+ channel with important roles in 
maintaining membrane potential and during the terminal phase of cardiac action 
potential repolarization. Several studies show a dominant negative effect of 
KCNJ2 mutation on Kir 2.1 channel function.