Rhabdomyolysis and fluctuating asymptomatic hyperCKemia associated with CACNA1S variant

Background and purpose: CACNA1S encodes Ca_v1.1, a voltage sensor for muscle excitation−contraction coupling, which activates the ryanodine receptor 1 (RYR1) leading to calcium release from the sarcoplasmic reticulum. CACNA1S mutations cause hypokalemic periodic paralysis, malignant hyperthermia and congenital myopathy. RYR1 mutations result in congenital myopathy, malignant hyperthermia and rhabdomyolysis. Methods: The aim was to describe a novel phenotype associated with a CACNA1S variant at a site previously linked to hypokalemic periodic paralysis. Results: The patient presented with fluctuating asymptomatic creatine kinase elevation after an episode of rhabdomyolysis but has no history of periodic paralysis. His muscle biopsy showed core-like structures occurring mainly in type 2 fibers. He carries a novel Ca_v1.1 variant (p.Arg528Leu) affecting a highly conserved amino acid. Different mutations at the same location cause hypokalemic periodic paralysis. Conclusion: This case underscores the similarity between the phenotypes caused by mutations in two functionally linked proteins, RYR1 and Ca_v1.1.