[Clinical and genetic analysis of a case of Triadin knockout syndrome due to variant of TRDN gene and a literature review].

Objective: To explore the genetic etiology and clinical phenotype of a child with Triadin knockout syndrome (TKOS), and to review the relevant literature of TKOS patients due to variants of TRDN gene.

Methods: A child who was admitted to the Children's Hospital of Xi'an Jiaotong University on March 19, 2023 due to sudden cardiac arrest 3 days earlier was selected as the study subject. Peripheral blood samples (2 to 3 mL) were collected from the child and her parents for the extraction of genomic DNA and whole exome sequencing (WES). Pathogenic variants were searched from databases such as the Genome Aggregation Database (gnomAD) and Online Mendelian Inheritance in Man (OMIM), and were assessed based on the guidelines from the American College of Medical Genetics and Genomics (ACMG). Sanger sequencing was carried out for family validation of the pathogenic variants. Using keywords such as "arrhythmias" "TRDN" and "Triadin" both in Chinese and English, relevant literature on TKOS patients due to variants of the TRDN gene was retrieved from the CNKI, Wanfang Data Knowledge Service Platform, and PubMed databases, and the time of literature retrieval was set from January 1, 2012 to December 1, 2023. This study has been approved by the Ethics Committee of the Affiliated Children's Hospital of Xi'an Jiaotong University (No. 20230097), and informed consent was obtained from the parents of the child.

Results: The child had experienced syncope and cardiac arrest after exercise. Electrocardiographic examination revealed QTc interval prolongation, T-wave inversion in precordial leads V1-V3, polymorphic ventricular premature beat (VPB), and ventricular tachycardia (VT) along with increased heart rate. WES and Sanger sequencing revealed that the child has harbored a homozygous c.463del(p.E155Kfs*20) variant of the TRDN gene, for which both of the parents were heterozygous. Based on the guidelines from the ACMG, the variant was classified as pathogenic (PVS1+PM2+PM3). The child was ultimately diagnosed with TKOS. In total 12 publications on TOKS cases caused by TRDN gene variants were retrieved, which involved 30 patients and 28 carriers of single heterozygous variant of the TRDN gene. Among the 30 TKOS patients, 20 had carried homozygous variants of the TRDN gene, and 10 had carried compound heterozygous variants, and all had exhibited significant clinical phenotype of arrhythmia, with most cases had experienced malignant arrhythmia induced by exercise and/or excitement during infancy or early childhood, leading to recurrent syncope and cardiac arrest. Of note, none of the 28 carriers of single heterozygous variant had abnormal clinical phenotype.

Conclusion: The homozygous c.463del(p.E155Kfs20) variant of the TRDN gene probably underlay the pathogenesis of cardiac arrest in this child. Above discovery has enriched the mutational spectrum of the TRDN gene.