SPEG (striated muscle enriched protein kinase) is a critical regulator of cardiac and skeletal muscle function, particularly in calcium homeostasis and excitation-contraction coupling. The protein maintains normal cardiac Ca2+ handling through transverse tubule formation and phosphorylation of junctional membrane complex proteins 1. SPEG interacts with key proteins including esterase D (Esd), Cardiomyopathy-Associated Protein 5 (Cmya5), and Fibronectin Type III and SPRY Domain Containing 2 (Fsd2) to stabilize excitation-contraction coupling complexes in triads and dyads 2. The gene has two main isoforms (Spegα and Spegβ) that display functional redundancy, with Spegα maintaining cardiac function when Spegβ is deficient 2. SPEG deficiency leads to Ca2+ leak, proteolytic cleavage of junctophilin-2, and disruption of transverse tubules 2. Mutations in SPEG cause centronuclear myopathy type 5, characterized by muscle weakness, delayed motor development, and centrally located nuclei in muscle fibers 3. The protein plays essential roles in muscle development, maintenance, triad development, and muscle regeneration 4. SPEG has been implicated in various cardiac diseases including dilated cardiomyopathy, heart failure, and atrial fibrillation 1.