Andersen-Tawil syndrome causing periodic weakness & palpitat
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The present case has been reported in the Indian Journal of Pediatrics.

An 11-y-old girl presented with one-year history of episodic 1–2 d of leg weakness provoked by physical exertion and recent onset episodes of palpitation and syncope. Her physical examination was significant for short stature (125 cm, 2.2 centiles), small chin, bilateral clinodactyly, and a mild weakness (4/5) of the bilateral iliopsoas muscles.

Laboratory testing revealed a low potassium level during the episodes of acute weakness. An EKG showed prolonged QTc interval and frequent premature ventricular contractions (PVCs) in bigeminal fashion. A multigene panel revealed a known pathogenic variant of KCNJ2 Arg 218 Trp, consistent with a diagnosis of Andersen-Tawil syndrome (ATS).

Potassium supplementation and acetazolamide provided remarkable improvement in the severity and frequency of her periodic weakness. However, her ventricular ectopy and tachycardia remained unresponsive to several antiarrhythmics such as flecainide, nadolol, and verapamil, and her cardiac symptoms ultimately abated after cardioverter-defibrillator (ICD) implantation.

Key takeaways:-
• ATS, the rarest form of periodic paralysis, is characterized by a triad of episodic muscle weakness, ventricular arrhythmias, and dysmorphic features due to pathogenic variants in the KCNJ2 gene which encodes inward rectifier potassium channel protein Kir 2.1

• Differential diagnosis of episodic flaccid weakness includes hypokalemic, hyperkalemic, and thyrotoxic periodic paralyses

• Episodes of acute weakness may respond to the correction of potassium concentration with or without chronic maintenance therapy

• Patients should avoid medicines that can prolong QT intervals

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