O-GlcNAcylation of CaMKII-S280 can downregulate K+ channel expression and function and further increase the susceptibility to arrhythmia in diabetes complicated with hyperglycemia; O-GlcNAcylation may limit the reuptake of Ca2+ from the sarcoplasmic reticulum, leading to impaired excitation–contraction coupling and arrhythmia in patients (human right atrial appendage and left ventricular tissue samples) with diabetes complicated with hyperglycemia [6,129,156]. The gene discussed is CAMK2G; the disease is diabetes mellitus.