Familial Dilated Cardiomyopathy Associated With a Novel Combination of Compound Heterozygous TNNC1 Variants

Maicon Landim-Vieira; Jamie R Johnston; Weizhen Ji; Emily K Mis; Joshua Tijerino; Michele Spencer-Manzon; Lauren Jeffries; E Kevin Hall; David Panisello-Manterola; Mustafa K Khokha; Engin Deniz; P Bryant Chase; Saquib A Lakhani; Jose Renato Pinto

doi:10.3389/fphys.2019.01612

Familial Dilated Cardiomyopathy Associated With a Novel Combination of Compound Heterozygous TNNC1 Variants

Front Physiol. 2020 Jan 22:10:1612. doi: 10.3389/fphys.2019.01612. eCollection 2019.

Authors

Affiliations

¹ Department of Biomedical Sciences, College of Medicine, Florida State University, Tallahassee, FL, United States.
² Pediatric Genomics Discovery Program, Department of Pediatrics, Yale School of Medicine, Yale University, New Haven, CT, United States.
³ Department of Genetics, Yale School of Medicine, Yale University, New Haven, CT, United States.
⁴ Department of Pediatrics, Yale School of Medicine, Yale University, New Haven, CT, United States.
⁵ Department of Biological Science, Florida State University, Tallahassee, FL, United States.

Abstract

Familial dilated cardiomyopathy (DCM), clinically characterized by enlargement and dysfunction of one or both ventricles of the heart, can be caused by variants in sarcomeric genes including TNNC1 (encoding cardiac troponin C, cTnC). Here, we report the case of two siblings with severe, early onset DCM who were found to have compound heterozygous variants in TNNC1: p.Asp145Glu (D145E) and p.Asp132Asn (D132N), which were inherited from the parents. We began our investigation with CRISPR/Cas9 knockout of TNNC1 in Xenopus tropicalis, which resulted in a cardiac phenotype in tadpoles consistent with DCM. Despite multiple maneuvers, we were unable to rescue the tadpole hearts with either human cTnC wild-type or patient variants to investigate the cardiomyopathy phenotype in vivo. We therefore utilized porcine permeabilized cardiac muscle preparations (CMPs) reconstituted with either wild-type or patient variant forms of cTnC to examine effects of the patient variants on contractile function. Incorporation of 50% WT/50% D145E into CMPs increased Ca²⁺ sensitivity of isometric force, consistent with prior studies. In contrast, incorporation of 50% WT/50% D132N, which had not been previously reported, decreased Ca²⁺ sensitivity of isometric force. CMPs reconstituted 50-50% with both variants mirrored WT in regard to myofilament Ca²⁺ responsiveness. Sinusoidal stiffness (SS) (0.2% peak-to-peak) and the kinetics of tension redevelopment (k _TR) at saturating Ca²⁺ were similar to WT for all preparations. Modeling of Ca²⁺-dependence of k _TR support the observation from Ca²⁺ responsiveness of steady-state isometric force, that the effects on each mutant (50% WT/50% mutant) were greater than the combination of the two mutants (50% D132N/50% D145E). Further studies are needed to ascertain the mechanism(s) of these variants.

Keywords: TNNC1; cardiac troponin C; dilated cardiomyopathy; genetic analysis; missense variant.