This changes the functions of the cardiac sodium channel and reduces sodium influx, thereby shortening the action potential time range and increasing the AF risk.[14] The SCN5A-H558R polymorphism is reportedly more common in patients with early-onset AF lacking traditional risk factors[15] than in controls, and the allele imparts a 1.6-fold increased risk of isolated AF occurrence. The gene discussed is SCN5A; the disease is atrial fibrillation.