Sivak, Erica L.

AbstractWhole exome sequencing (WES) was used to determine the primary cause of muscle disorder in a family diagnosed with a mild, undetermined myopathy and malignant hyperthermia (MH) susceptibility (MHS). WES revealed the compound heterozygous mutations, p.Ile235Asn and p.Glu982Lys, in ATP2A1, encoding the sarco(endo)plasmic reticulum Ca2+ ATPase type 1 (SERCA1), a calcium pump, expressed in fast‐twitch muscles. Recessive mutations in ATP2A1 are known to cause Brody myopathy, a rare muscle disorder characterized by exercise‐induced impairment of muscle relaxation and stiffness. Analyses of affected muscles showed the absence of SERCA1, but SERCA2 upregulation in slow and fast myofibers, suggesting a compensatory mechanism that partially restores the diminished Ca2+ transport in Brody myopathy. This compensatory adaptation to the lack of SERCA1 Ca2+ pumping activity within the muscle explains, in part, the mild course of disease in our patient. Diagnosis of MHS in this family was secondary to a loss of SERCA1 due to disease‐associated mutations. Although there are obvious differences in clinical expression and molecular mechanisms between MH and Brody myopathy, a feature common to both conditions is elevated myoplasmic Ca2+ content. Prolonged intracellular Ca2+ elevation is likely to have led to MHS diagnosis in vitro and postoperative MH‐like symptoms in Brody patient.