Novel junctophilin-2 mutation A405S is associated with basal septal hypertrophy and diastolic dysfunction.
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BACKGROUND:Hypertrophic cardiomyopathy (HCM), defined as asymmetric left ventricular hypertrophy, is a leading cause of cardiac death in the young. Perturbations in calcium (Ca2+) handling proteins have been implicated in the pathogenesis of HCM. JPH2-encoded junctophilin 2 is a major component of the junctional membrane complex, the subcellular microdomain involved in excitation-contraction coupling. We hypothesized that a novel JPH2 mutation identified in patients with HCM is causally linked to HCM, and alters intracellular Ca2+ signaling in a pro-hypertrophic manner. OBJECTIVES:To determine using a transgenic mouse model whether a JPH2 mutation found in a HCM patient is responsible for disease development. METHODS:Genetic interrogation of a large cohort of HCM cases was conducted for all coding exons of JPH2. Pseudo-knock-in (PKI) mice containing a novel JPH2 variant were subjected to echocardiography, cardiac MRI, hemodynamic analysis, and histology. RESULTS:A novel JPH2 mutation, A405S, was identified in a genotype-negative proband with significant basal septal hypertrophy. Although initially underappreciated by traditional echocardiographic imaging, PKI mice with this JPH2 mutation (residue A399S in mice) were found to exhibit similar basal hypertrophy using a newly developed echo imaging plane, and this was confirmed using cardiac MRI. Histological analysis demonstrated cardiomyocyte hypertrophy and disarray consistent with HCM. CONCLUSIONS:Variant A405S is a novel HCM-associated mutation in JPH2 found in a proband negative for mutations in the canonical HCM-associated genes. Studies in the analogous mouse model demonstrated for the first time a causal link between a JPH2 defect and HCM. Moreover, novel imaging approaches identified subvalvular septal hypertrophy, specific findings also reported in the human JPH2 mutation carrier.
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Quick, AP, AP Landstrom, Q Wang, DL Beavers, JO Reynolds, G Barreto-Torres, V Tran, J Showell, et al. (2017). Novel junctophilin-2 mutation A405S is associated with basal septal hypertrophy and diastolic dysfunction. JACC. Basic to translational science, 2(1). pp. 56–67. 10.1016/j.jacbts.2016.11.004 Retrieved from https://hdl.handle.net/10161/20304.
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Dr. Landstrom is a physician scientist who specializes in the care of children and young adults with arrhythmias, heritable cardiovascular diseases, and sudden unexplained death syndromes. As a clinician, he is trained in pediatric cardiology with a focus on arrhythmias and genetic diseases of the heart. He specializes in caring for patients with heritable arrhythmia (channelopathies) such as long QT syndrome, Brugada syndrome, catecholaminergic polymorphic ventricular tachycardia, and short QT syndrome. He also specializes in the evaluation of children following a cardiac arrest or after the sudden and unexplained death of a family member. He has expertise in cardiovascular genetics and uses it to identify individuals in a family who may be at risk of a disease, even if all clinical testing is negative. As a scientist, he is trained in genetics and cell biology. He runs a research lab exploring the genetic and molecular causes of arrhythmias, sudden unexplained death syndromes, and heart muscle disease (cardiomyopathies). He utilizes patient-derived induced pluripotent stem cells and genetic mouse models to identify the mechanisms of cardiovascular genetic disease with the goal of developing novel therapies.
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