Ryanodinopathies: Muscle Disorders Linked to Mutations in Ry- anodine Receptors

Excitation-contraction (EC) coupling in skeletal and cardiac muscle depends on bidirectional signaling interactions between sarcolemmal L-type Ca channels (or dihydropyridine receptors, DHPRs) and Ca release channels (or ryanodine receptors, RyRs) of the sarcoplasmic reticulum (SR). Mutations in the skeletal muscle RyR (RyR1) result in several clinically distinct muscle disorders including malignant hyperthermia (MH), central core disease (CCD), multi-minicore disease (MmD), and nemaline rod myopathy (NM). Similarly, two inherited exercise-induced arrhythmogenic disorders, catecholaminergic polymorphic ventricular tachycardia (CPVT) and arrhythmogenic right ventricular dysplasia type-2 (ARVD2), are linked to mutations in the cardiac isoform of the RyR (RyR2). This review examines the genetics, pathophysiology, and clinical/diagnostic characteristics of the “ryanodinopathies,” an emerging and eclectic array of clinically distinct muscle disorders that arise from genetic and functional defects in the skeletal and cardiac muscle RyRs.