Recent studies at Weill Cornell Medical College show that two gene products that are essential to the coordinated rhythm of heart muscle are also involved in thyroid hormone production. The proteins called KCNE2 ad KCNQ1 are known to be involved in cardiac arrhythmias and the recent studies show that inherited mutations can also cause thyroid dysfunction.
KCNQ1 and KCNE2 form potassium chanels in cardiac muscle that help each heartbeat in a timely way. Inherited mutations cause ventricular and atrial cardiac arrhytmias. It used to be thought that the dysfunction was limited to cardiac muscle. The new studies show that these mutations can also cause thyroid dysfunction.
With inadequate thyroid hormone, an affected person may experience fatigue and lowered heart rate. With adequate thyroid hormone, both thyroid and heart function may improve.
Source: New Genetic Link Between Cardiac Arrhythmias and Thryoid Dysfunction Identified, new York Presbyterian Hospital/Weill Cornell Medical Center, Sept 2009.