Andersen–Tawil syndrome (ATS) is caused by mutations in the KCNJ2 gene, which encodes Kir2.1, in patients exhibiting cardiac arrhythmia, periodic paralysis, dental defects, cleft lip/palate, micrognathia, hypertelorism, low-set ears, and limb patterning defects. Here, KCNJ2 is linked to periodic paralysis.