Definition:

Andersen-Tawil syndrome (ATS) is a distinct type of periodic paralysis characterized in its full form by a triad of cardiac abnormalities, distinctive facial and skeletal features, and periodic paralysis. The distinctive physical features considered characteristic of ATS are: broad forehead, hypoplastic mandible, hypotelorism, low-set ears, digit clinodactyly, and 2-3 syndactyly of the toes. It is obvious that ATS has a high degree of phenotypic heterogeneity. ATS patients have loss-of-function mutations in the KCNJ2 gene, which encodes the voltage-gated inward rectifier potassium channel, Kir2.1. However, described KCNJ2 mutations only account for approximately 60% of diagnoses, suggesting genetic heterogeneity.