HCN4 and chronic atrial and intestinal dysrhythmia: Third, a substitution in the N-terminal domain of Sgo1 (K23E) disrupts its ability to directly interact with the pacemaker ion channel HCN4 in the membrane of cardiomyocytes of patients with Chronic Atrial and Intestinal Dysrhythmia Syndrome (CAID)(Liu et al., 2021).