Olson, Timothy M

Background Idiopathic dilated cardiomyopathy ( DCM ) is typically diagnosed in adulthood, yet familial cases exhibit variable age‐dependent penetrance and a subset of patients develop sporadic DCM in childhood. We sought to discover the molecular basis of sporadic DCM in an 11‐year‐old female with severe heart failure necessitating cardiac transplantation. Methods and Results Parental echocardiograms excluded asymptomatic DCM . Whole exome sequencing was performed on the family trio and filtered for rare, deleterious, recessive, and de novo variants. Of the 8 candidate genes identified, only 2 had a role in cardiac physiology. A de novo missense mutation in TNNT 2 was identified, previously reported and functionally validated in familial DCM with markedly variable penetrance. Additionally, recessive compound heterozygous truncating mutations were identified in XIRP 2 , a member of the ancient Xin gene family, which governs intercalated disc ( ICD ) maturation. Histomorphological analysis of explanted heart tissue revealed misregistration, mislocalization, and shortening of ICD s, findings similar to Xirp2 −/− mice. Conclusions The synergistic effects of TNNT 2 and XIRP 2 mutations, resulting in perturbed sarcomeric force generation and transmission, respectively, would account for an early‐onset heart failure phenotype. Whereas the importance of Xin proteins in cardiac development has been well established in animal models, this study implicates XIRP 2 as a novel modifier gene in the pathogenesis of DCM .

We previously reported that the cardiomyocyte-specific leucine-rich repeat containing protein (LRRC)10 has critical functions in the mammalian heart. In the present study, we tested the role of LRRC10 in the response of the heart to biomechanical stress by performing transverse aortic constriction on Lrrc10-null ( Lrrc10−/−) mice. Mild pressure overload induced severe cardiac dysfunction and ventricular dilation in Lrrc10−/−mice compared with control mice. In addition to dilation and cardiomyopathy, Lrrc10−/−mice showed a pronounced increase in heart weight with pressure overload stimulation and a more dramatic loss of cardiac ventricular performance, collectively suggesting that the absence of LRRC10 renders the heart more disease prone with greater hypertrophy and structural remodeling, although rates of cardiac fibrosis and myocyte dropout were not different from control mice. Lrrc10−/−cardiomyocytes also exhibited reduced contractility in response to β-adrenergic stimulation, consistent with loss of cardiac ventricular performance after pressure overload. We have previously shown that LRRC10 interacts with actin in the heart. Here, we show that His150of LRRC10 was required for an interaction with actin, and this interaction was reduced after pressure overload, suggesting an integral role for LRRC10 in the response of the heart to mechanical stress. Importantly, these experiments demonstrated that LRRC10 is required to maintain cardiac performance in response to pressure overload and suggest that dysregulated expression or mutation of LRRC10 may greatly sensitize human patients to more severe cardiac disease in conditions such as chronic hypertension or aortic stenosis.

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.

Idiopathic dilated cardiomyopathy is a heritable, genetically heterogeneous disorder characterized by progressive heart failure. Dilated cardiomyopathy typically exhibits autosomal dominant inheritance, yet frequently remains clinically silent until adulthood. We sought to discover the molecular basis of idiopathic, non‐syndromic dilated cardiomyopathy in a one‐month‐old male presenting with severe heart failure. Previous comprehensive testing of blood, urine, and skin biopsy specimen was negative for metabolic, mitochondrial, storage, and infectious etiologies. Ophthalmologic examination was normal. Chromosomal microarray and commercial dilated cardiomyopathy gene panel testing failed to identify a causative mutation. Parental screening echocardiograms revealed no evidence of clinically silent dilated cardiomyopathy. Whole exome sequencing was carried out on the family trio on a research basis, filtering for rare, deleterious, recessive and de novo genetic variants. Pathogenic compound heterozygous truncating mutations were identified in ALMS1, diagnostic of Alström syndrome and prompting disclosure of genetic findings. Alström syndrome is a known cause for dilated cardiomyopathy in children yet delayed and mis‐diagnosis are common owing to its rarity and age‐dependent emergence of multisystem clinical manifestations. At six months of age the patient ultimately developed bilateral nystagmus and hyperopia, features characteristic of the syndrome. Early diagnosis is guiding clinical monitoring of other organ systems and allowing for presymptomatic intervention. Furthermore, recognition of recessive inheritance as the mechanism for sporadic disease has informed family planning. This case highlights a limitation of standard gene testing panels for pediatric dilated cardiomyopathy and exemplifies the potential for whole exome sequencing to solve a diagnostic dilemma and enable personalized care. © 2015 Wiley Periodicals, Inc.

Background— Genetic studies of cardiomyopathy and heart failure have limited throughput in mammalian models. Adult zebrafish have been recently pursued as a vertebrate model with higher throughput, but genetic conservation must be tested. Methods and Results— We conducted transcriptome analysis of zebrafish heart and searched for fish homologues of 51 known human dilated cardiomyopathy–associated genes. We also identified genes with high cardiac expression and genes with differential expression between embryonic and adult stages. Among tested genes, 30 had a single zebrafish orthologue, 14 had 2 homologues, and 5 had ≥3 homologues. By analyzing the expression data on the basis of cardiac abundance and enrichment hypotheses, we identified a single zebrafish gene for 14 of 19 multiple-homologue genes and 2 zebrafish homologues of high priority for ACTC1 . Of note, our data suggested vmhc and vmhcl as functional zebrafish orthologues for human genes MYH6 and MYH7 , respectively, which are established molecular markers for cardiac remodeling. Conclusions— Most known genes for human dilated cardiomyopathy have a corresponding zebrafish orthologue, which supports the use of zebrafish as a conserved vertebrate model. Definition of the cardiac transcriptome and fetal gene program will facilitate systems biology studies of dilated cardiomyopathy in zebrafish.

Background— The goal of this study was to identify genetic determinants of plasma N-terminal proatrial natriuretic peptide (NT-proANP) in the general community by performing a large-scale genetic association study and to assess its functional significance in in vitro cell studies and on disease susceptibility. Methods and Results— Genotyping was performed across 16 000 genes in 893 randomly selected individuals, with replication in 891 subjects from the community. Plasma NT-proANP 1–98 concentrations were determined using a radioimmunoassay. Thirty-three genome-wide significant single-nucleotide polymorphisms were identified in the MTHFR-CLCN6-NPPA-NPPB locus and were all replicated. To assess the significance, in vitro functional genomic studies and clinical outcomes for carriers of a single-nucleotide polymorphism rs5063 (V32M) located in NPPA that represented the most significant variation in this genetic locus were assessed. The rs5063 variant allozyme in transfected HEK293 cells was decreased to 55±8% of wild-type protein ( P =0.01) as assessed by quantitative western blots. Carriers of rs5063 had lower NT-proANP levels (1427 versus 2291 pmol/L; P <0.001) and higher diastolic blood pressures (75 versus 73 mm Hg; P =0.009) and were at an increased risk of stroke when compared with wild-type subjects independent of age, sex, diabetes mellitus, hypertension, atrial fibrillation, and cholesterol levels (hazard ratio, 1.6; P =0.004). Conclusions— This is the first large-scale genetic association study of circulating NT-proANP levels performed with replication and functional assessment that identified genetic variants in the MTHFR-CLCN6-NPPA-NPPB cluster to be significantly associated with NT-proANP levels. The clinical significance of this variation is related to lower NT-proANP levels, higher blood pressures, and an increased risk of stroke in the general community.

Abstract Aims Exome sequencing was used to genotype comprehensively a Takotsubo (stress) cardiomyopathy (TC) cohort, enabling investigation of a vast 486 gene network for adrenergic signalling. Methods and results Twenty-eight TC subjects, including a mother–daughter pair and five recurrent cases, underwent whole-exome sequencing. Frequencies of 17 common, functional adrenergic polymorphisms were statistically similar to those of population controls. Filtering for rare, predicted-deleterious, catecholamine/adrenergic signalling variants revealed heterozygosity in 55 genes in TC cases and 59 genes in healthy controls. Overall allele burden was similar and did not discriminate clinical variables among TC subjects, but gene identities were largely cohort specific, and TC cases were enriched for variants within functional domains (68% vs. 48%, P = 0.031). Two-thirds of TC cases carried more than one filtered adrenergic pathway variant, and 11 genes harboured a variant in ≥2 cases. The mother–daughter pair shared missense variants in highly conserved functional domains of ADH5, CACNG1, EPHA4, and PRKCA. An adrenergic pathway-independent analysis of the cohort exposed no common gene for TC. Conclusions Overall, these data support genetic heterogeneity in TC susceptibility and a likely polygenic basis, conferring a cumulative effect on adrenergic pathway dysregulation in a subset of individual subjects. Study of larger cohorts and non-coding regulatory regions is warranted to define genetic risk factors for TC further.

Mammalian heart development is built on highly conserved molecular mechanisms with polygenetic perturbations resulting in a spectrum of congenital heart diseases (CHD). However, knowledge of cardiogenic ontogeny that regulates proper cardiogenesis remains largely based on candidate-gene approaches. Mapping the dynamic transcriptional landscape of cardiogenesis from a genomic perspective is essential to integrate the knowledge of heart development into translational applications that accelerate disease discovery efforts toward mechanistic-based treatment strategies. Herein, we designed a time-course transcriptome analysis to investigate the genome-wide dynamic expression landscape of innate murine cardiogenesis ranging from embryonic stem cells to adult cardiac structures. This comprehensive analysis generated temporal and spatial expression profiles, revealed stage-specific gene functions, and mapped the dynamic transcriptome of cardiogenesis to curated pathways. Reconciling known genetic underpinnings of CHD, we deconstructed a disease-centric dynamic interactome encoded within this cardiogenic atlas to identify stage-specific developmental disturbances clustered on regulation of epithelial-to-mesenchymal transition (EMT), BMP signaling, NF-AT signaling, TGFb-dependent EMT, and Notch signaling. Collectively, this cardiogenic transcriptional landscape defines the time-dependent expression of cardiac ontogeny and prioritizes regulatory networks at the interface between health and disease.

We analyzed the phenotype associated with the atrial natriuretic peptide (ANP) genetic variant rs5065 in a random community-based sample. We also assessed and compared the biological action of 2 concentrations (10 −10 mol/L, 10 –8 mol/L) of ANP and ANP-RR, the protein variant encoded by the minor allele of rs5065, on activation of the guanylyl cyclase (GC)-A and GC-B receptors, production of the second messenger 3′,5′-cGMP in endothelial cells, and endothelial permeability. rs5065 genotypes were determined in a cross-sectional adult cohort from Olmsted County, MN (n=1623). Genotype frequencies for rs5065 were 75%, 24%, and 1% for TT, TC, and CC, respectively. Multivariate analysis showed that the C allele was associated with increased risk of cerebrovascular accident (hazard ratio, 1.43; 95% confidence interval, 1.09–1.86; P =0.009) and higher prevalence of myocardial infarction (odds ratio, 1.82; 95% confidence interval, 1.07–3.09; P =0.026). ANP-RR 10 −8 mol/L activated the GC-A receptor (83.07±8.31 versus no treatment 0.18±0.04 per 6 wells; P =0.006), whereas ANP-RR 10 −10 mol/L did not. Neither 10 −8 mol/L nor 10 −10 mol/L ANP-RR activated GC-B receptor ( P =0.10, P =0.35). ANP 10 −8 mol/L and ANP-RR 10 −8 mol/L stimulated 3′,5′-cGMP production in endothelial cells similarly ( P =0.58). Both concentrations of ANP-RR significantly enhanced human aortic endothelial cell permeability (69 versus 29 relative fluorescence units [RFUs], P =0.012; 58 versus 39 RFUs, P =0.015) compared with ANP. The minor allele of rs5065 was associated with increased cardiovascular risk. ANP-RR activated the GC-A receptor, increased 3′,5′-cGMP in endothelial cells, and when compared with ANP, augmented endothelial cell permeability.