Basic/Translational Science -> Genomics: Translational D-AB19 - Basic Science: What Lies Beneath (ID 20) Abstract

D-AB19-01 - Phenotype-guided Whole Genome Analysis In A Patient With Genetically Elusive Long Qt Syndrome Yields A Novel Trdn-Encoded Triadin Pathogenetic Substrate For Triadin Knockout Syndrome And Reveals A Novel Primate-specific Cardiac Trdn Transcript (ID 779)

Disclosure
 D.J. Clemens: Nothing relevant to disclose.

Abstract

Background: Triadin Knockout Syndrome (TKOS) is a rare arrhythmia disorder caused by recessive null variants in TRDN-encoded cardiac triadin 1 (CT1). TKOS is characterized by extensive T-wave inversions in precordial leads V1-V4, QT prolongation, and a severe disease expression of exercise-induced cardiac arrest in early childhood. The 8 exon CT1 isoform (286 amino acids) is considered the only triadin isoform present in human heart.
Objective: To elucidate the underlying genetic mechanism of disease in a genetically elusive patient displaying a characteristic TKOS phenotype.
Methods: After negative commercial testing, genome sequencing and a TRDN gene specific trio analysis was completed on a patient with QT prolongation, T-wave inversions, and cardiac arrest at 18 months of age. Both parents were unaffected. RNA and protein isolated from patient-specific, re-engineered cardiomyocytes were used to determine the effects of the identified variants using RT-PCR and western blot.
Results: Genome sequencing revealed compound heterozygous putative splice-error variants (maternal c.22+29 A>G and paternal c.484+1189 G>A). The maternal variant has been reported previously in TKOS patients. The novel, paternally-derived c.484+1189 G>A variant is located within 24 base pairs of a predicted alternative exon 6 (6a) which resides within the intron between canonical exons 5 and 6. We determined that this previously unrecognized exon 6a produces a short TRDN transcript, which is predicted by Ensembl to be primate-specific, and potentially a novel 167 amino acid protein isoform in normal human heart tissue. The c.484+1189 G>A variant not only results in abnormal splicing of the 6a containing transcript leading to a frame-shift mutation, but also results in the abolishment of the primary 8 exon CT1 transcript.
Conclusion: Here, we present evidence for a novel alternative exon 6a-containing TRDN transcript in normal heart. This patient’s novel, deep intronic TRDN variant causes a splicing-error of a newly recognized exon 6a and a complete loss of triadin. Considering that both TRDN variants in this patient were missed following commercial testing, these results underscore the importance of genome sequencing to reveal pathogenic intronic variants.
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