Abstract 12669: Identification of Novel Genetic Modifiers of LQT2 by Combining Patient Derived iPS Derived Cardiomyocytes and Exome Sequencing
Background: Long QT Syndrome Type 2 (LQT2) is caused by autosomal dominant loss-of-function in hERG, but often with incomplete penetrance. We investigated the mechanisms underlying genotype-phenotype discordance seen in a large LQT2 family by studying cardiac myocytes derived from induced pluripotent stem cells from affected and unaffected mutation-positive family members. We hypothesize that the presence of disease modifying genes contributes to this phenotype.
Methods: Two family pairs displaying this genotype-phenotype discordance were studied. iPS cells were generated from skin biopsies and differentiated into ventricular cardiomyocytes (iPS-CM) that were studied electrophysiologically. Exome sequencing was also performed on the four subjects.
Results: hERG R752W mutation-positive cardiomyocytes exhibited reduced IKr compared to control cells. Further, cardiomyocytes from the affected individuals displayed prolonged action potentials as well as greater L-type calcium current (LTCC) compared to cells from control subjects and an unaffected mutation-positive family member. Whole exome sequencing identified two potential disease-modifying genes. The first is a single nucleotide variant (SNV) in KCNK17 encoding a 2-pore potassium channel. When expressed in Chinese Hamster Ovary cells, this variant potassium channel, which was found only in asymptomatic mutation-positive individuals, leads to increased current density compared to the nonvariant channel. The second SNV was identified in a Ras-like GTPase and was present exclusively in symptomatic mutation-positive individuals. Overexpression of this variant protein in iCells© resulted in a significant increase in LTCC.
Conclusion: We have successfully recapitulated the genotype-phenotype discordance seen in a LQT2 family using patient-derived iPS-CMs. We postulate that the difference in the currents conferred by the 2-pore potassium channel variant could partially protect hERG R752W mutation-positive subjects by mitigating the severity of the hERG mutation. However, it appears that ultimately the inheritance of a SNV in a Ras-like GTPase in tandem with the primary mutation in hERG is the permutation that drives the complete disease phenotype.
Author Disclosures: S. Chai: None. X. Wan: None. E. Ficker: None. A. Ramirez-Navarro: None. E.S. Kaufman: None. A.L. George: None. I. Deschenes: None.
- © 2015 by American Heart Association, Inc.