Spectrum and Prevalence of CALM1-, CALM2-, and CALM3-Encoded Calmodulin Variants in Long QT Syndrome and Functional Characterization of a Novel Long QT Syndrome-Associated Calmodulin Missense Variant, E141G.

BACKGROUND: Calmodulin (CaM) is encoded by 3 genes, CALM1, CALM2, and CALM3, all of which harbor pathogenic variants linked to long QT syndrome (LQTS) with early and severe expressivity. These LQTS-causative variants reduce CaM affinity to Ca(2+) and alter the properties of the cardiac L-type calcium channel (CaV1.2). CaM also modulates NaV1.5 and the ryanodine receptor, RyR2. All these interactions may play a role in disease pathogenesis. Here, we determine the spectrum and prevalence of pathogenic CaM variants in a cohort of genetically elusive LQTS, and functionally characterize the novel variants. METHODS AND RESULTS: Thirty-eight genetically elusive LQTS cases underwent whole-exome sequencing to identify CaM variants. Nonsynonymous CaM variants were over-represented significantly in this heretofore LQTS cohort (13.2%) compared with exome aggregation consortium (0.04%; P<0.0001). When the clinical sequelae of these 5 CaM-positive cases were compared with the 33 CaM-negative cases, CaM-positive cases had a more severe phenotype with an average age of onset of 10 months, an average corrected QT interval of 676 ms, and a high prevalence of cardiac arrest. Functional characterization of 1 novel variant, E141G-CaM, revealed an 11-fold reduction in Ca(2+)-binding affinity and a functionally dominant loss of inactivation in CaV1.2, mild accentuation in NaV1.5 late current, but no effect on intracellular RyR2-mediated calcium release. CONCLUSIONS: Overall, 13% of our genetically elusive LQTS cohort harbored nonsynonymous variants in CaM. Genetic testing of CALM1-3 should be pursued for individuals with LQTS, especially those with early childhood cardiac arrest, extreme QT prolongation, and a negative family history.

Confirmation of cause and manner of death via a comprehensive cardiac autopsy including whole exome next-generation sequencing.

Annually, the sudden death of thousands of young people remains inadequately explained despite medicolegal investigation. Postmortem genetic testing for channelopathies/cardiomyopathies may illuminate a potential cardiac mechanism and establish a more accurate cause and manner of death and provide an actionable genetic marker to test surviving family members who may be at risk for a fatal arrhythmia. Whole exome sequencing allows for simultaneous genetic interrogation of an individual's entire estimated library of approximately 30000 genes. Following an inconclusive autopsy, whole exome sequencing and gene-specific surveillance of all known major cardiac channelopathy/cardiomyopathy genes (90 total) were performed on autopsy blood-derived genomic DNA from a previously healthy 16-year-old adolescent female found deceased in her bedroom. Whole exome sequencing analysis revealed a R249Q-MYH7 mutation associated previously with familial hypertrophic cardiomyopathy, sudden death, and impaired ß-myosin heavy chain (MHC-ß) actin-translocating and actin-activated ATPase (adenosine triphosphatase) activity. Whole exome sequencing may be an efficient and cost-effective approach to incorporate molecular studies into the conventional postmortem examination.