A novel homozygous mutation in the TRDN gene causes a severe form of pediatric malignant ventricular arrhythmia

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. 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. 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. 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. 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.