Heart Rhythm 2020 Feb 19;17(2):296-304. Epub 2019 Aug 19.
Vita-Salute San Raffaele University, Milan, Italy; Genomic Unit for the Diagnosis of Human Pathologies, Division of Genetics and Cellular Biology, IRCCS San Raffaele Hospital, Milan, Italy. Electronic address:
Background: Triadin is a protein expressed in cardiac and skeletal muscle that has an essential role in the structure and functional regulation of calcium release units and excitation-contraction coupling. Mutations in the triadin gene (TRDN) have been described in different forms of human arrhythmia syndromes with early onset and severe arrhythmogenic phenotype, including triadin knockout syndrome.
Objective: The purpose of this study was to characterize the pathogenetic mechanism underlying a case of severe pediatric malignant arrhythmia associated with a defect in the TRDN gene.
Methods: We used a trio whole exome sequencing approach to identify the genetic defect in a 2-year-old boy who had been resuscitated from sudden cardiac arrest and had frequent episodes of ventricular fibrillation and a family history positive for sudden death. We then performed in vitro functional analysis to investigate possible pathogenic mechanisms underlying this severe phenotype.
Results: We identified a novel homozygous missense variant (p.L56P) in the TRDN gene in the proband that was inherited from the heterozygous unaffected parents. Expression of a green fluorescent protein (GFP)-tagged mutant human cardiac triadin isoform (TRISK32-L56P-GFP) in heterologous systems revealed that the mutation alters protein dynamics. Furthermore, when co-expressed with the type 2 ryanodine receptor, caffeine-induced calcium release from TRISK32-L56P-GFP was relatively lower compared to that observed with the wild-type construct.
Conclusion: The results of this study allowed us to hypothesize a pathogenic mechanism underlying this rare arrhythmogenic recessive form, suggesting that the mutant protein potentially can trigger arrhythmias by altering calcium homeostasis.