FHOD3 deficiency disrupts sarcomere organization and activates CaMKII signaling in human stem cell-derived cardiomyocytes

• FHOD3 knockout in human stem cell-derived cardiomyocytes leads to severe sarcomere disorganization, impaired calcium handling, and mitochondrial dysfunction, culminating in reduced contractility. • Transcriptomic profiling reveals downregulation of sarcomere and calcium-handling genes, with enrichment in cardiomyopathy and calcium signaling pathways. • FHOD3 deficiency activates CaMKII signaling via phosphorylation at Thr286, a known driver of cardiac hypertrophy and heart failure progression. • The myosin activator Omecamtiv mecarbil partially restores contractility in FHOD3-deficient cardiomyocytes, suggesting a potential therapeutic approach for FHOD3-related cardiomyopathy.