Patient-specific induced pluripotent stem cell properties implicate Ca2+-homeostasis in clinical arrhythmia associated with combined heterozygous RYR2 and SCN10A variants

<p class="MsoNormal"><span>We illustrate the use of induced pluripotent stem cells (iPSCs) as platforms for investigating cardiomyocyte phenotypes in a human family pedigree exemplified by novel heterozygous RYR2-A1855D and SCN10A-Q1362H variants occurring alone and in combination. The proband, a four-month-old boy, presented with </span><span>polymorphic</span><span> ventricular tachycardia (</span><span>P</span><span>VT). Genetic tests revealed double novel heterozygous RYR2-A1855D and SCN10A-Q1362H variants inherited from his father (F) and mother (M) respectively. His father showed ventricular premature beats (VPB); his mother was asymptomatic. Molecular biological characterisations demonstrated greater <em>TNNT2</em> mRNA expression in the iPSCs-induced cardiomyocytes (iPS-CMs) than in the iPSCs</span><span>.</span><span> </span><span>c</span><span>TNTs became progressively organised, but cytoplasmic RYR2 and SCN10A aggregations occurred in the iPS-CMs. Proband-specific iPS-CMs showed decreased <em>RYR2</em> and <em>SCN10A</em> mRNA expression. The RYR2-A1855D variant resulted in premature spontaneous sarcoplasmic reticular (SR) Ca²⁺ transients (PCTs), Ca²⁺ oscillations (COs), and increased action potential durations (APDs). SCN10A-Q1362H did not confer any specific phenotype. However, the </span><span>combined </span><span>heterozygous RYR2-A1855D and SCN10A-Q1362H variants in the proband iPS-CMs resulted in accentuated Ca²⁺ homeostasis disorders, AP prolongation and susceptibility to early afterdepolarisations (EADs) at high stimulus frequencies. These findings attribute the clinical phenotype in the proband to effects of the heterozygous <em>RYR2</em> variant exacerbated by heterozygous <em>SCN10A</em> modification. </span></p>