Andersen-Tawil syndrome (ATS) is an autosomal-dominant channelopathy resulting in episodic attacks of muscle weakness, cardiac arrythmias, and dystinctive physical features. Episodic muscle weakness can be associated with a concomitant hypo-, normo-, or hyperkalemia. Ventricular arrythmias and QT prolongation in electrocardiograms are the most common cardiac manifestations. The dysmorphology includes craniofacial (hypertelorism, low-set ears, and micrognathia), dental abnormalities (delayed teeth development, missing teeth, and abnormal positioning) and skeletal abnormalities of the trunk and limbs (short stature, scoliosis, clinodactyly, and syndactyly). Molecular genetic analysis has revealed that ATS is caused by mutations in the KCNJ2 gene (OMIM #600681) located on chromosome 17q23.1-q24.2. The KCNJ2 gene encodes a pore-forming subunit of the inward rectifier potassium channel, Kir2.1. The majority of ATS patients have missense mutations which inhibit normal channel function through a dominant negative effect. A wide range of penetrance and severity of clinical phenotypes exists and it can make diagnosis difficult. we report an ATS patient with an apparently sporadic presentation, who carries a novel de novo mutation in the KCNJ2 gene. This mutation predicts a codon change from glycine to alanine at residue 146 (Gly146Ala, c.437G＞C), which is located at the extracellular pore loop region of Kir2.1. The patient did not respond to acetazolamide and showed a marked improvement of the paralytic symptoms on treatment with a combination of spironolactone, amiloride, and potassium supplements.