Genomics and innovative induced pluripotent stem cell (iPSC) modeling to improve understanding of pathomechanisms underlying Brugada syndrome (BrS)

Brugada syndrome (BrS) is an inherited cardiac arrhythmia disorder that predisposes patients to ventricular fibrillation and sudden cardiac death. This event mainly occurs in young adults, who often do not experience any prior symptoms. Over 20 genes have so far been reported to be involved in BrS development, but contemporary knowledge about the pathomechanisms underlying BrS is limited and about 70% of the patients remain genetically undiagnosed. Also, no suitable pharmacological therapies exist. Identification of novel genes underlying BrS can contribute important knowledge on disease mechanisms and reveal potential therapeutic targets, and as such formed the general aim of this thesis. While heterologous expression models remain a gold standard in studies of single causal mutations for cardiac arrhythmias, iPSC models provide a solution to study more complex cases, where a sum of multiple factors is at play for the expression of the phenotype. In this thesis, evaluation of the applicability of iPSC-derived cardiomyocytes (iPSC-CM) in BrS studies was performed by modeling a known BrS SCN5A Belgian founder mutation (c.4813+3_4813+6dupGGGT). The previously reported variant loss-of-function effect on a single channel level observed in a heterologous expression model, was observed in the generated iPSC-CMs. Nevertheless, there was variability in the observed results, suggesting immaturity of the cell model and existence of other factors which modulate the expression of the observed phenotypes. In the Cardiogenetics clinic at the Antwerp University Hospital, extensive phenotypic information was collected on BrS families in which genetic screening with an in-house developed cardiac arrhythmia gene panel did not yield any result. Three of those families became the basis for this project, in which a combined linkage analysis and whole-genome sequencing approach was used to look for potential disease-causing variants. The applied genetic screening identified a significantly linked region on Chromosome 2 in one of the families, however without identification of a clear candidate variant. Also in the other unresolved families no strong candidate variant was identified. Next, BrS modeling was performed in iPSC-CMs from two patients and one unaffected relative of the family showing linkage, to gain insights on the disease mechanism. While in literature reports iPSC-CM models of genotype-negative BrS patients did not show phenotypical changes, in this PhD project the patient-derived iPSC-CMs displayed a BrS phenotype with either sodium current reduction and/or calcium handling abnormalities, encouraging further investigation. The obtained results suggest different underlying disease mechanisms within one family, which underscores the complex nature of BrS.

Publication year:2022

Keywords:Doctoral thesis

Accessibility:Open