Sudden death due to malignant hyperthermia with a mutation of RYR1: autopsy, morphology and genetic analysis

Next-generation sequencing and bioinformatics to identify genetic causes of malignant hyperthermia

BACKGROUND/PURPOSE

Malignant hyperthermia (MH) is a life-threatening pharmacogenetic disease with only two known causative genes, RYR1 and CACNA1S. Both are huge genes containing numerous exons, and they reportedly only account for 50-70% of known MH patients. Next-generation sequencing (NGS) technology and bioinformatics could help delineate the genetic diagnosis of MH and several MH-like clinical presentations.

METHODS

We established a capture-based targeted NGS sequencing framework to examine the whole genomic regions of RYR1, CACNA1S and the 16.6 Kb mitochondrial genome, as well as 12 other genes related to excitation-contraction coupling and/or skeletal muscle calcium homeostasis. We applied bioinformatics analyses to the variants identified in this study and also to the 48 documented RYR1 pathogenic variants.

RESULTS

The causative variants were identified in seven of the eight (87.5%) MH families, but in none of the 10 individuals classified as either normal controls (N = 2) or patients displaying MH-like clinical features later found to be caused by other etiologies (N = 8). We showed that RYR1 c.1565A>G (p.Tyr522Cys)(rs118192162) could be a genetic hot spot in the Taiwanese population. Bioinformatics analyses demonstrated low population frequencies and predicted damaging effects from all known pathogenic RYR1 variants. We estimated that more than one in 1149 individuals worldwide carry MH pathogenic variants at RYR1.

CONCLUSION

NGS and bioinformatics are sensitive and specific tools to examine RYR1 and CACNA1S for the genetic diagnosis of MH. Pathogenic variants in RYR1 can be found in the majority of MH patients in Taiwan.

Sudden unexpected cardiac death and postmortem identification of a novel RYR2 gene mutation

A 13-year-old female was found lifeless at home. The autopsy and consecutive histological and toxicological examinations showed blood-rich and edematous lungs and foamy bloody content in the airways. No morphologic pathological findings were seen, especially no bleeding sources. Toxicological findings were unremarkable. The specific cause of death remained unclear. Due to reported losses of consciousness, a moleculargenetic postmortem testing was performed. A so far undescribed mutation in the cardiac ryanodine receptor gene RyR2 was detected. This mutation is suitable to explain the case history as well as the morphological findings. The cardiac ryanodine receptor gene RyR2 encodes the ryanodine receptor type 2, an ion channel in the cardiomyocytes. The ion channel regulates the influx of calcium ions and thus influences myocardial activity. Mutations in this channel may result in the catecholaminergic polymorphic ventricular tachycardia (CPVT), a cardiac arrhythmia that can lead to syncope and sudden cardiac death. This case demonstrates the usefulness and need of molecular autopsy, in particular to identify and treat possibly affected family members.