Exome Sequencing Reveals Novel Rare Variants in the Ryanodine Receptor and Calcium Channel Genes in Malignant Hyperthermia Families

Abstract

Background About half of malignant hyperthermia (MH) cases are associated with skeletal muscle ryanodine receptor 1 (RYR1) and calcium channel, voltage-dependent, L type, α1S subunit (CACNA1S) gene mutations, leaving many with an unknown cause. We chose to apply a sequencing approach to uncover causal variants in unknown cases. Sequencing the exome, the protein-coding region of the genome, has power at low sample sizes and identified the cause of over a dozen Mendelian disorders. Methods We considered four families with multiple MH cases but in whom no mutations in RYR1 and CACNA1S had been identified by Sanger sequencing of complementary DNA. Exome sequencing of two affecteds per family, chosen for maximum genetic distance, were compared. Variants were ranked by allele frequency, protein change, and measures of conservation among mammals to assess likelihood of causation. Finally, putative pathogenic mutations were genotyped in other family members to verify cosegregation with MH. Results Exome sequencing revealed 1 rare RYR1 nonsynonymous variant in each of 3 families (Asp1056His, Val2627Met, Val4234Leu), and 1 CACNA1S variant (Thr1009Lys) in a 4th family. These were not seen in variant databases or in our control population sample of 5379 exomes. Follow-up sequencing in other family members verified cosegregation of alleles with MH. Conclusions Using both exome sequencing and allele frequency data from large sequencing efforts may aid genetic diagnosis of MH. In our sample, it was more sensitive for variant detection in known genes than Sanger sequencing of complementary DNA, and allows for the possibility of novel gene discovery.

Germline mutations in RYR1 are associated with foetal akinesia deformation sequence/lethal multiple pterygium syndrome

“…Thus initially RYR1 mutations were described in individuals susceptible to malignant hyperthermia (MHS) [17,18]. RYR1 mutations associated with MHS are typically heterozygous missense substitutions [19][20][21]. Subsequently RYR1 mutations were described in the context of a variety of histological subtypes of congenital myopathies including central core disease, minicore/centronuclear myopathy with external ophthalmoplegia, centronuclear myopathy and congenital fibre-type disproportion [22][23][24].…”

Triadopathies: An Emerging Class of Skeletal Muscle Diseases

“…Initial efforts using whole exome sequencing have largely resulted in validation of RYR1 mutations as the primary cause of disease in the majority of cases [11,16]. These studies have also revealed many RYR1 variants of unknown significance that require further validation in order to be listed as pathogenic.…”

“…It is now clear that RYR1-related myopathies are the most common nondystrophic muscle conditions of childhood and that the clinical spectrum for the disorders is vast [36,37]. One important issue to emerge is how to interpret identified sequence variants in RYR1 that are of uncertain pathogenicity [11,16]. AS RYR1 mutations are associated with such a broad range of disease, most novel variants identified in RYR1 have the potential of causing disease.…”

Malignant hyperthermia and the clinical significance of type-1 ryanodine receptor gene (RYR1) variants: proceedings of the 2013 MHAUS Scientific Conference

“…Drs. Hopkins and Kim 41 analyzed RYR1 and CACNA1S variants identified using WES in 5,379 of individuals as part of the National Heart, Lung, and Blood Institute (NHLBI) Grand Opportunity (GO) Exome Sequencing Project (ESP). Their analyses showed that RYR1 is more genetically diverse than 74–79% of other genes in European-Americans and African Americans, while CACNA1S is more genetically diverse than 77–82% of other genes in these cohorts.…”