CALCR and osteoporosis: While deficient CT can be replenished with exogenous CT-analogues (e.g. miacalcin, salmon CT) already in clinical use (e.g. for Paget’s disease, hypercalcaemia, osteoporosis), strategies to restore atrial CTR expression in persAF, a prerequisite for CT-mediated atrial anti-fibrotic and anti-arrhythmic effects, do not exist.