Susceptibility to Ventricular Arrhythmias Resulting from Mutations in <i>FKBP1B</i>, <i>PXDNL</i>, and <i>SCN9A</i> Evaluated in hiPSC Cardiomyocytes
Héctor Barajas-Martínez, Maya Landenhed Smith, Dan Hu, Robert J. Goodrow, Colleen Puleo, Can Hasdemir, Charles Antzelevitch, Ryan Pfeiffer, Jacqueline A. Treat, Jonathan M. Cordeiro
Abstract
Background . We report an inherited cardiac arrhythmia syndrome consisting of Brugada and Early Repolarization Syndrome associated with variants in SCN9A , PXDNL , and FKBP1B . The proband inherited the 3 mutations and exhibited palpitations and arrhythmia-mediated syncope, whereas the parents and sister, who carried one or two of the mutations, were asymptomatic. Methods and Results . We assessed the functional impact of these mutations in induced pluripotent stem cell cardiomyocytes (hiPSC-CMs) derived from the proband and an unaffected family member. Current and voltage clamp recordings, as well as confocal microscopy analysis of Ca 2+ transients, were evaluated in hiPSC-CMs from the proband and compared these results with hiPSC-CMs from undiseased controls. Genetic analysis using next-generation DNA sequencing revealed heterozygous mutations in SCN9A , PXDNL , and FKBP1B in the proband. The proband displayed right bundle branch block and exhibited episodes of syncope. The father carried a mutation in FKBP1B , whereas the mother and sister carried the SCN9A mutation. None of the 3 family members screened developed cardiac events. Action potential recordings from control hiPSC-CM showed spontaneous activity and a low upstroke velocity. In contrast, the hiPSC-CM from the proband showed irregular spontaneous activity. Confocal microscopy of the hiPSC-CM of the proband revealed low fluorescence intensity Ca 2+ transients that were episodic in nature. Patch-clamp measurements in hiPSC-CM showed no difference in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M1"><mml:msub><mml:mrow><mml:mi>I</mml:mi></mml:mrow><mml:mrow><mml:mtext>Na</mml:mtext></mml:mrow></mml:msub></mml:math> but reduced <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M2"><mml:msub><mml:mrow><mml:mi>I</mml:mi></mml:mrow><mml:mrow><mml:mtext>Ca</mml:mtext></mml:mrow></mml:msub></mml:math> in the proband compared with control. Coexpression of PXDNL -R391Q with SCN5A -WT displayed lower <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M3"><mml:msub><mml:mrow><mml:mi>I</mml:mi></mml:mrow><mml:mrow><mml:mtext>Na</mml:mtext></mml:mrow></mml:msub></mml:math> density compared to PXDNL -WT. In addition, coexpression of PXDNL -R391Q with KCND3 -WT displayed significantly higher <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M4"><mml:msub><mml:mrow><mml:mi>I</mml:mi></mml:mrow><mml:mrow><mml:mtext>to</mml:mtext></mml:mrow></mml:msub></mml:math> density compared to PXDNL -WT. Conclusion . SCN9A , PXDNL , and FKBP1B variants appeared to alter spontaneous activity in hiPSC-CM. Only the proband carrying all 3 mutations displayed the ERS/BrS phenotype, whereas one nor two mutations alone did not produce the clinical phenotype. Our results suggest a polygenic cause of the BrS/ERS arrhythmic phenotype due to mutations in these three gene variants caused a very significant loss of function of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M5"><mml:msub><mml:mrow><mml:mi>I</mml:mi></mml:mrow><mml:mrow><mml:mtext>Na</mml:mtext></mml:mrow></mml:msub></mml:math> and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M6"><mml:msub><mml:mrow><mml:mi>I</mml:mi></mml:mrow><mml:mrow><mml:mtext>Ca</mml:mtext></mml:mrow></mml:msub></mml:math> and gain of function of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M7"><mml:msub><mml:mrow><mml:mi>I</mml:mi></mml:mrow><mml:mrow><mml:mtext>to</mml:mtext></mml:mrow></mml:msub></mml:math>.