CASQ2 (Calsequestrin 2): CASQ2 is a protein involved in calcium storage within the sarcoplasmic reticulum of cardiac muscle cells. It plays a key role in regulating calcium balance and cardiac muscle contraction. Mutations in CASQ2 are associated with catecholaminergic polymorphic ventricular tachycardia, a condition characterized by irregular heartbeats triggered by physical activity or stress.