Theis, Jeanne L.

AbstractGenetics is a significant factor contributing to congenital heart disease (CHD), but our understanding of the genetic players and networks involved in CHD pathogenesis is limited. Here, we searched for de novo copy number variations (CNVs) in a cohort of 167 CHD patients to identify DNA segments containing potential pathogenic genes. Our search focused on new candidate disease genes within 19 deleted de novo CNVs, which did not cover known CHD genes. For this study, we developed an integrated high-throughput phenotypical platform to probe for defects in cardiogenesis and cardiac output in human induced pluripotent stem cell (iPSC)-derived multipotent cardiac progenitor (MCPs) cells and, in parallel, in the Drosophila in vivo heart model. Notably, knockdown (KD) in MCPs of RPL13, a ribosomal gene and SON, an RNA splicing cofactor, reduced proliferation and differentiation of cardiomyocytes, while increasing fibroblasts. In the fly, heart-specific RpL13 KD, predominantly at embryonic stages, resulted in a striking ‘no heart’ phenotype. KD of Son and Pdss2, among others, caused structural and functional defects, including reduced or abolished contractility, respectively. In summary, using a combination of human genetics and cardiac model systems, we identified new genes as candidates for causing human CHD, with particular emphasis on ribosomal genes, such as RPL13. This powerful, novel approach of combining cardiac phenotyping in human MCPs and in the in vivo Drosophila heart at high throughput will allow for testing large numbers of CHD candidates, based on patient genomic data, and for building upon existing genetic networks involved in heart development and disease.

Background: Spontaneous coronary artery dissection (SCAD) is an uncommon idiopathic disorder predominantly affecting young, otherwise healthy women. Rare familial cases reveal a genetic predisposition to disease. The aim of this study was to identify a novel susceptibility gene for SCAD. Methods: Whole-exome sequencing was performed in a family comprised of 3 affected individuals and filtered to identify rare, predicted deleterious, segregating variants. Immunohistochemical staining was used to evaluate protein expression of the identified candidate gene. The prevalence and spectrum of rare (<0.1%) variants within binding domains was determined by next-generation sequencing or denaturing high-performance liquid chromatography in a sporadic SCAD cohort of 675 unrelated individuals. Results: We identified a rare heterozygous missense variant within a highly conserved β-integrin–binding domain of TLN1 segregating with familial SCAD. TLN1 encodes talin 1—a large cytoplasmic protein of the integrin adhesion complex that links the actin cytoskeleton and extracellular matrix. Consistent with high mRNA expression in arterial tissues, robust immunohistochemical staining of talin 1 was demonstrated in coronary arteries. Nine additional rare heterozygous missense variants in TLN1 were identified in 10 sporadic cases. Incomplete penetrance, suggesting genetic or environmental modifiers of this episodic disorder, was evident in the familial case and 5 individuals with sporadic SCAD from whom parental DNA was available. Conclusions: Our findings reveal TLN1 as a disease-associated gene in familial and sporadic SCAD and, together with abnormal vascular phenotypes reported in animal models of talin 1 disruption, implicate impaired structural integrity of the coronary artery cytoskeleton in SCAD susceptibility.

Background— The molecular underpinnings of hypoplastic left heart are poorly understood. Staged surgical palliation has dramatically improved survival, yet eventual failure of the systemic right ventricle necessitates cardiac transplantation in a subset of patients. We sought to identify genetic determinants of hypoplastic left heart with latent right ventricular dysfunction in individuals with a Fontan circulation. Methods and Results— Evaluation of cardiac structure and function by echocardiography in patients with hypoplastic left heart and their first-degree relatives identified 5 individuals with right ventricular ejection fraction ≤40% after Fontan operation. Whole genome sequencing was performed on DNA from 21 family members, filtering for genetic variants with allele frequency <1% predicted to alter protein structure or expression. Secondary family-based filtering for de novo and recessive variants revealed rare inherited missense mutations on both paternal and maternal alleles of MYH6 , encoding myosin heavy chain 6, in 2 patients who developed right ventricular dysfunction 3 to 11 years postoperatively. Parents and siblings who were heterozygous carriers had normal echocardiograms. Protein modeling of the 4 highly conserved amino acid substitutions, residing in both head and tail domains, predicted perturbation of protein structure and function. Conclusions— In contrast to dominant MYH6 mutations with variable penetrance identified in other congenital heart defects and dilated cardiomyopathy, this study reveals compound heterozygosity for recessive MYH6 mutations in patients with hypoplastic left heart and reduced systemic right ventricular ejection fraction. These findings implicate a shared molecular basis for the developmental arrest and latent myopathy of left and right ventricles, respectively.

Background— Mutations in myofilament proteins, most commonly MYBPC3 -encoded myosin-binding protein C and MYH7 -encoded β-myosin heavy chain, can cause hypertrophic cardiomyopathy (HCM). Despite significant advances in structure-function relationships pertaining to the cardiac sarcomere, there is limited knowledge of how a mutation leads to clinical HCM. We, therefore, set out to study expression and localization of myofilament proteins in left ventricular tissue of patients with HCM. Methods and Results— Frozen surgical myectomy specimens from 47 patients with HCM were examined and genotyped for mutations involving 8 myofilament-encoding genes. Myofilament protein levels were quantified by Western blotting with localization graded from immunohistochemical staining of tissue sections. Overall, 25 of 47 (53%) patients had myofilament-HCM, including 12 with MYBPC3-HCM and 9 with MYH7-HCM. As compared with healthy heart tissue, levels of myofilament proteins were increased in patients manifesting a mutation in either gene. Patients with a frameshift mutation predicted to truncate MYBPC3 exhibited marked disturbances in protein localization as compared with missense mutations in either MYBPC3 or MYH7 . Conclusions— In this first expression study in human HCM tissue, increased myofilament protein levels in patients with either MYBPC3 - or MYH7- mediated HCM suggest a poison peptide mechanism. Specifically, the mechanism of dysfunction may vary according to the genetic subgroup suggested by a distinctly abnormal distribution of myofilament proteins in patients manifesting a truncation mutation in MYBPC3 .