Andersen-Tawil syndrome

Andersen-Tawil syndrome, also called long QT syndrome type 7, is a rare genetic disorder that disrupts the heart's electrical rhythm along with skeletal development and muscle control. About 60 percent of cases, classified as Type 1, arise from mutations in the KCNJ2 gene, while Type 2 cases show no identified mutation; the condition is inherited in an autosomal dominant pattern, so one mutated copy is sufficient to cause it. Three groups of features define the syndrome: cardiac abnormalities such as a prolonged QT interval and irregular heart rhythms; skeletal features including a small lower jaw, low-set ears and curved fingers; and intermittent muscle weakness known as hypokalaemic periodic paralysis, usually triggered by low blood potassium. The disorder is extraordinarily rare, estimated at about one person per million, with only around 200 documented cases as of 2013.