Novel variants in ryanodine receptor type 3 predispose to acute rhabdomyolysis due to impaired autophagy

Rhabdomyolysis is the acute breakdown of skeletal muscle resulting from failure of cellular homeostasis in response to metabolic stress. Recurrent forms are frequently linked to inherited defects affecting energy metabolism or calcium handling. Ryanodine receptor type 3 (RyR3) is an intracellular calcium release channel, expressed in skeletal muscle, that contributes to the fine-tuning of calcium signaling. Although variants in other calcium-handling proteins have been implicated in rhabdomyolysis, the role of RyR3 has not been established. In this study, we report rare compound heterozygous missense variants in RYR3 identified in two unrelated individuals with severe, fever-triggered recurrent rhabdomyolysis. Muscle biopsies revealed mild structural changes with triadic disorganization, mitochondrial alterations, lipid accumulation, and autophagic material, while overall muscle architecture was largely preserved. Structural modeling supports the pathogenicity of the variants, and calcium flux analysis demonstrated significantly reduced ryanodine receptor-mediated calcium release in patient-derived myoblasts. Functional analyses showed that RyR3 deficiency impaired starvation-induced autophagy, characterized by defective autophagosome formation and reduced autophagic flux, and increased susceptibility to metabolic stress. Mitochondrial bioenergetic profiling revealed reduced oxidative phosphorylation capacity and decreased membrane potential under stress conditions, consistent with compromised mitochondrial adaptation. In zebrafish, ryr3 knockdown resulted in structural and functional muscle abnormalities, including reduced myotome area and decreased locomotor activity, associated with impaired autophagic flux. This study establishes a novel association between recessive RYR3 variants and recurrent rhabdomyolysis and identifies RyR3 as a critical regulator of skeletal muscle stress adaptation through calcium-dependent control of autophagy and mitochondrial homeostasis. More broadly, our findings further highlight autophagy as a central determinant of muscle resilience in the context of rhabdomyolysis.