CASQ2 and sick sinus syndrome: Familial sick sinus syndrome has also been linked to mutations in KvLQT1 (Kcnq1), Kir2.1 (Kcnj2), and calsequestrin 2 (Casq2)27, all of which show a significant day-night rhythm (Kcnq1, P = 0.015; Kcnj2, P = 0.00017; Ryr2, P = 0.044; Casq2, P = 0.0080).