A further clinical indication regarding the role of a specific ion current in human SAN pacemaker activity involves the slowly activating delayed rectifier K+ current (IKs) and comes from patients who suffer from the long-QT syndrome type 1 and carry a loss-of-function mutation in the KCNQ1 (KvLQT1) gene, encoding the pore-forming α-subunit of the IKs channel. This evidence concerns the gene KCNQ1 and long QT syndrome 1.