Assessement of the pathogenic role of a missense variant in a benign autosomal dominant myopathy with hyperCKaemia

Chronic elevation of serum creatine kinase (CK) levels is a common manifestation of neuromuscular disorders and may precede clinical expression of the disease. Many patients however, although with persistently increased CK, are asymptomatic or present with very mild disease. Among conditions presenting with high CK as only clinical sign, there is malignant hyperthermia, a life-threatening condition that is usually triggered by exposure to certain drugs used for general anaesthesia. In 7 patients from 3 unrelated Italian families having high CK and a mild myopathy, the muscle biopsy showed the presence of inclusions within muscle fibers that were positive to calsequestrin. Calsequestrin is part of a protein complex involved in the storage and release of calcium in muscle fibers, necessary for muscle contraction. Analysis of the CASQ1 gene which encodes calsequestrin 1, revealed a mutation in an aminoacid highly conserved among species. Calsequestrin 1 and 2 isoforms expressed in skeletal muscle and heart are codified by 2 different genes and have dissimilar calcium binding capacities. Mutations in the CASQ2 gene are responsible for ventricular arrhythmias and sudden cardiac death. In the CASQ1 gene no mutations have been found so far; however in mice genetic ablation of the CASQ1 gene causes a disease quite similar to malignant hyperthermia. The present project aims to verify if the CASQ1 mutation found in our patients is responsible for the increased CK levels or for malignant hyperthermia. We will genetically manipulate cells so to introduce the mutation and will perform proteomic analysis to assess the mutated protein characteristics; and, by electrophysiological studies, we will evaluate how the mutation affects calcium uptake and release. Finally, we will extend CASQ1 gene analysis to other sporadic and familial cases of hyperCKaemia or with susceptibility to malignant hyperthermia.