Publications by authors named "Timothy M Olson"

73 Publications

From Safety to Benefit in Cell Delivery During Surgical Repair of Ebstein Anomaly: Initial Results.

Ann Thorac Surg 2021 Feb 1. Epub 2021 Feb 1.

Wanek HLHS Consortium Clinical Pipeline, Mayo Clinic, Rochester, Minnesota, USA.

Background: The objective of this study is to assess the safety and early impact of intramyocardial delivery of autologous bone marrow-derived mononuclear cells (BM-MNC) at time of surgical Ebstein repair.

Methods: Patients with EA (ages 6 months to 30 years) scheduled to undergo repair of the TV were eligible to participate in this open label, non-randomized Phase I clinical trial. BM-MNC target dose was 1-3 million cells/kg. Ten patients have undergone surgical intervention and cell delivery to the right ventricle (RV) and completed 6 month follow-up.

Results: All patients underwent surgical tricuspid valve repair and uneventful BM-MNC delivery; there were no ventricular arrhythmias and no adverse events related to study product or delivery. Echocardiographic RV myocardial performance index improved and RV fractional area change showed an initial decline and then through study follow-up. There was no evidence of delayed myocardial enhancement or regional wall motion abnormalities at injection sites on 6-month follow-up MRI.

Conclusions: Intramyocardial delivery of BM-MNC following surgical repair in EA can be performed safely. Echocardiography variables suggest a positive impact of cell delivery on the RV myocardium with improvements in both RV size and wall motion over time. Additional follow-up and comparison to control groups are required to better characterize the impact of cell therapy on the myopathic RV in Ebstein anomaly.
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http://dx.doi.org/10.1016/j.athoracsur.2020.11.065DOI Listing
February 2021

Genetic Association Between Hypoplastic Left Heart Syndrome and Cardiomyopathies.

Circ Genom Precis Med 2021 Feb 16;14(1):e003126. Epub 2020 Dec 16.

Cardiovascular Genetics Research Laboratory (J.L.T., R.S.S., T.M.O.), Mayo Clinic, Rochester, MN.

Background: Hypoplastic left heart syndrome (HLHS) with risk of poor outcome has been linked to variants, implicating overlap in genetic etiologies of structural and myopathic heart disease.

Methods: Whole genome sequencing was performed in 197 probands with HLHS, 43 family members, and 813 controls. Data were filtered for rare, segregating variants in 3 index families comprised of an HLHS proband and relative(s) with cardiomyopathy. Whole genome sequencing data from cases and controls were compared for rare variant burden across 56 cardiomyopathy genes utilizing a weighted burden test approach, accounting for multiple testing using a Bonferroni correction.

Results: A pathogenic nonsense variant was identified in the first proband who underwent cardiac transplantation for diastolic heart failure, her father with left ventricular noncompaction, and 2 fourth-degree relatives with hypertrophic cardiomyopathy. A likely pathogenic missense variant was identified in the second proband, a second-degree relative with aortic dilation, and a fourth-degree relative with dilated cardiomyopathy. A pathogenic exon 3 in-frame deletion was identified in the third proband diagnosed with catecholaminergic polymorphic ventricular tachycardia and his father with left ventricular noncompaction and catecholaminergic polymorphic ventricular tachycardia. To further investigate HLHS-cardiomyopathy gene associations in cases versus controls, rare variant burden testing of 56 genes revealed enrichment in (=0.000068). Rare, predicted-damaging variants were identified in 10% of probands in our cohort-4 with familial congenital heart disease, 4 with compound heterozygosity (3 with systolic ventricular dysfunction), and 4 with - synergistic heterozygosity.

Conclusions: Whole genome sequencing in multiplex families, proband-parent trios, and case-control cohorts revealed defects in cardiomyopathy-associated genes in patients with HLHS, which may portend impaired functional reserve of the single-ventricle circulation.
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http://dx.doi.org/10.1161/CIRCGEN.120.003126DOI Listing
February 2021

Dysregulated ribonucleoprotein granules promote cardiomyopathy in RBM20 gene-edited pigs.

Nat Med 2020 11 13;26(11):1788-1800. Epub 2020 Nov 13.

Discovery Engine/Todd and Karen Wanek Family Program for Hypoplastic Left Heart Syndrome, Mayo Clinic, Rochester, MN, USA.

Ribonucleoprotein (RNP) granules are biomolecular condensates-liquid-liquid phase-separated droplets that organize and manage messenger RNA metabolism, cell signaling, biopolymer assembly, biochemical reactions and stress granule responses to cellular adversity. Dysregulated RNP granules drive neuromuscular degenerative disease but have not previously been linked to heart failure. By exploring the molecular basis of congenital dilated cardiomyopathy (DCM) in genome-edited pigs homozygous for an RBM20 allele encoding the pathogenic R636S variant of human RNA-binding motif protein-20 (RBM20), we discovered that RNP granules accumulated abnormally in the sarcoplasm, and we confirmed this finding in myocardium and reprogrammed cardiomyocytes from patients with DCM carrying the R636S allele. Dysregulated sarcoplasmic RBM20 RNP granules displayed liquid-like material properties, docked at precisely spaced intervals along cytoskeletal elements, promoted phase partitioning of cardiac biomolecules and fused with stress granules. Our results link dysregulated RNP granules to myocardial cellular pathobiology and heart failure in gene-edited pigs and patients with DCM caused by RBM20 mutation.
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http://dx.doi.org/10.1038/s41591-020-1087-xDOI Listing
November 2020

Patient-specific genomics and cross-species functional analysis implicate LRP2 in hypoplastic left heart syndrome.

Elife 2020 10 2;9. Epub 2020 Oct 2.

Development, Aging and Regeneration, Sanford Burnham Prebys Medical Discovery Institute, La Jolla, United States.

Congenital heart diseases (CHDs), including hypoplastic left heart syndrome (HLHS), are genetically complex and poorly understood. Here, a multidisciplinary platform was established to functionally evaluate novel CHD gene candidates, based on whole-genome and iPSC RNA sequencing of a HLHS family-trio. Filtering for rare variants and altered expression in proband iPSCs prioritized 10 candidates. siRNA/RNAi-mediated knockdown in healthy human iPSC-derived cardiomyocytes (hiPSC-CM) and in developing and zebrafish hearts revealed that LDL receptor-related protein is required for cardiomyocyte proliferation and differentiation. Consistent with hypoplastic heart defects, compared to patents the proband's iPSC-CMs exhibited reduced proliferation. Interestingly, rare, predicted-damaging LRP2 variants were enriched in a HLHS cohort; however, understanding their contribution to HLHS requires further investigation. Collectively, we have established a multi-species high-throughput platform to rapidly evaluate candidate genes and their interactions during heart development, which are crucial first steps toward deciphering oligogenic underpinnings of CHDs, including hypoplastic left hearts.
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http://dx.doi.org/10.7554/eLife.59554DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7581429PMC
October 2020

Identification of Susceptibility Loci for Spontaneous Coronary Artery Dissection.

JAMA Cardiol 2020 May 6. Epub 2020 May 6.

Department of Cardiovascular Medicine, Mayo Clinic, Rochester, Minnesota.

Importance: Spontaneous coronary artery dissection (SCAD), an idiopathic disorder that predominantly affects young to middle-aged women, has emerged as an important cause of acute coronary syndrome, myocardial infarction, and sudden cardiac death.

Objective: To identify common single-nucleotide variants (SNVs) associated with SCAD susceptibility.

Design, Setting, And Participants: This single-center genome-wide association study examined approximately 5 million genotyped and imputed SNVs and subsequent SNV-targeted replication analysis results in individuals enrolled in the Mayo Clinic SCAD registry from August 30, 2011, to August 2, 2018. Data analysis was performed from June 21, 2017, to December 30, 2019.

Main Outcomes And Measures: Genetic loci and positional candidate genes associated with SCAD.

Results: This study included 484 white women with SCAD (mean [SD] age, 46.6 [9.2] years) and 1477 white female controls in the discovery cohort (mean [SD] age, 64.0 [14.5] years) and 183 white women with SCAD (mean [SD] age, 47.1 [9.9] years) and 340 white female controls in the replication cohort (mean [SD] age, 51.0 [15.3] years). Associations with SCAD risk reached genome-wide significance at 3 loci (1q21.3 [OR, 1.78; 95% CI, 1.51-2.09; P = 2.63 × 10-12], 6p24.1 [OR, 1.77; 95% CI, 1.51-2.09; P = 7.09 × 10-12], and 12q13.3 [OR, 1.67; 95% CI, 1.42-1.97; P = 3.62 × 10-10]), and 7 loci had evidence suggestive of an association (1q24.2 [OR, 2.10; 95% CI, 1.58-2.79; P = 2.88 × 10-7], 3q22.3 [OR, 1.47; 95% CI, 1.26-1.71; P = 6.65 × 10-7], 4q34.3 [OR, 1.84; 95% CI, 1.44-2.35; P = 9.80 × 10-7], 8q24.3 [OR, 2.57; 95% CI, 1.76-3.75; P = 9.65 × 10-7], 15q21.1 [OR, 1.75; 95% CI, 1.40-2.18; P = 7.23 × 10-7], 16q24.1 [OR, 1.91; 95% CI, 1.49-2.44; P = 2.56 × 10-7], and 21q22.11 [OR, 2.11; 95% CI, 1.59-2.82; P = 3.12 × 10-7]) after adjusting for the top 5 principal components. Associations were validated for 5 of the 10 risk alleles in the replication cohort. In a meta-analysis of the discovery and replication cohorts, associations for the 5 SNVs were significant, with relatively large effect sizes (1q21.3 [OR, 1.77; 95% CI, 1.54-2.03; P = 3.26 × 10-16], 6p24.1 [OR, 1.71; 95% CI, 1.49-1.97; P = 4.59 × 10-14], 12q13.3 [OR, 1.69; 95% CI, 1.47-1.94; P = 1.42 × 10-13], 15q21.1 [OR, 1.79; 95% CI, 1.48-2.17; P = 2.12 × 10-9], and 21q22.11 [OR, 2.18; 95% CI, 1.70-2.81; P = 1.09 × 10-9]). Each index SNV was within or near a gene highly expressed in arterial tissue and previously linked to SCAD (PHACTR1) and/or other vascular disorders (LRP1, LINC00310, and FBN1).

Conclusions And Relevance: This study revealed 5 replicated risk loci and positional candidate genes for SCAD, most of which are associated with extracoronary arteriopathies. Moreover, the alternate alleles of 3 SNVs have been previously associated with atherosclerotic coronary artery disease, further implicating allelic susceptibility to coronary artery atherosclerosis vs dissection.
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http://dx.doi.org/10.1001/jamacardio.2020.0872DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7203673PMC
May 2020

Model system identification of novel congenital heart disease gene candidates: focus on RPL13.

Hum Mol Genet 2019 12;28(23):3954-3969

Development, Aging and Regeneration Program, Sanford-Burnham Prebys Medical Discovery Institute, La Jolla, CA, USA.

Genetics 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.
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http://dx.doi.org/10.1093/hmg/ddz213DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7202142PMC
December 2019

Hypoplastic Left Heart Syndrome: An Overview for Primary Care Providers.

Pediatr Rev 2019 Jul;40(7):344-353

Wanek Family Program for Hypoplastic Left Heart Syndrome.

Hypoplastic left heart syndrome is one of the most complex congenital heart diseases and requires several cardiac surgeries for survival. The diagnosis is usually established prenatally or shortly after birth. Each stage of surgery poses a unique hemodynamic situation that requires deeper understanding to manage common pediatric problems such as dehydration and respiratory infections. Careful multidisciplinary involvement in the care of these complex patients is improving their outcome; however, morbidity and mortality are still substantial. In this review, we focus on the hemodynamic aspects of various surgical stages that a primary care provider should know to manage these challenging patients.
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http://dx.doi.org/10.1542/pir.2018-0005DOI Listing
July 2019

Rare Missense Variants in TLN1 Are Associated With Familial and Sporadic Spontaneous Coronary Artery Dissection.

Circ Genom Precis Med 2019 04 19;12(4):e002437. Epub 2019 Mar 19.

Cardiovascular Genetics Research Laboratory (T.N.T., J.L.T., R.S.S., T.M.O.), Mayo Clinic, Rochester, MN.

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.
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http://dx.doi.org/10.1161/CIRCGEN.118.002437DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6625931PMC
April 2019

Association of the PHACTR1/EDN1 Genetic Locus With Spontaneous Coronary Artery Dissection.

J Am Coll Cardiol 2019 01;73(1):58-66

INSERM, Paris Cardiovascular Research Center, Paris, France; Faculty of Medicine, Paris-Descartes University, Sorbonne Paris Cité, Paris, France. Electronic address:

Background: Spontaneous coronary artery dissection (SCAD) is an increasingly recognized cause of acute coronary syndromes (ACS) afflicting predominantly younger to middle-aged women. Observational studies have reported a high prevalence of extracoronary vascular anomalies, especially fibromuscular dysplasia (FMD) and a low prevalence of coincidental cases of atherosclerosis. PHACTR1/EDN1 is a genetic risk locus for several vascular diseases, including FMD and coronary artery disease, with the putative causal noncoding variant at the rs9349379 locus acting as a potential enhancer for the endothelin-1 (EDN1) gene.

Objectives: This study sought to test the association between the rs9349379 genotype and SCAD.

Methods: Results from case control studies from France, United Kingdom, United States, and Australia were analyzed to test the association with SCAD risk, including age at first event, pregnancy-associated SCAD (P-SCAD), and recurrent SCAD.

Results: The previously reported risk allele for FMD (rs9349379-A) was associated with a higher risk of SCAD in all studies. In a meta-analysis of 1,055 SCAD patients and 7,190 controls, the odds ratio (OR) was 1.67 (95% confidence interval [CI]: 1.50 to 1.86) per copy of rs9349379-A. In a subset of 491 SCAD patients, the OR estimate was found to be higher for the association with SCAD in patients without FMD (OR: 1.89; 95% CI: 1.53 to 2.33) than in SCAD cases with FMD (OR: 1.60; 95% CI: 1.28 to 1.99). There was no effect of genotype on age at first event, P-SCAD, or recurrence.

Conclusions: The first genetic risk factor for SCAD was identified in the largest study conducted to date for this condition. This genetic link may contribute to the clinical overlap between SCAD and FMD.
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http://dx.doi.org/10.1016/j.jacc.2018.09.085DOI Listing
January 2019

Cell-Based Therapy for Myocardial Dysfunction After Fontan Operation in Hypoplastic Left Heart Syndrome.

Mayo Clin Proc Innov Qual Outcomes 2017 Sep 2;1(2):185-191. Epub 2017 Aug 2.

Division of Pediatric Cardiology, Mayo Clinic, Rochester, MN.

Myocardial dysfunction after Fontan palliation for univentricular congenital heart disease is a challenging clinical problem. The medical treatment has a limited impact, with cardiac transplant being the ultimate management step. Cell-based therapies are evolving as a new treatment for heart failure. Phase 1 clinical trials using regenerative therapeutic strategies in congenital heart disease are ongoing. We report the first case of autologous bone marrow-derived mononuclear cell administration for ventricular dysfunction, 23 years after Fontan operation in a patient with hypoplastic left heart syndrome. The cells were delivered into the coronary circulation by cardiac catheterization. Ventricular size decreased and several parameters reflecting ventricular function improved, with maximum change noted 3 months after cell delivery. Such regenerative therapeutic options may help in delaying and preventing cardiac transplant.
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http://dx.doi.org/10.1016/j.mayocpiqo.2017.07.002DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6134900PMC
September 2017

Idiopathic Restrictive Cardiomyopathy in Children and Young Adults.

Am J Cardiol 2018 05 12;121(10):1266-1270. Epub 2018 Feb 12.

Department of Pediatric and Adolescent Medicine/Division of Pediatric Cardiology, Mayo Clinic, Rochester, Minnesota; Department of Cardiovascular Diseases/Division of Pediatric Cardiology, Mayo Clinic, Rochester, Minnesota. Electronic address:

Idiopathic restrictive cardiomyopathy (IRC) is a rare condition characterized by reduced ventricular compliance. Children with IRC have poor outcomes with most patients proceeding to cardiac transplantation. We sought to analyze our institutional experience and assess contemporary outcomes for children with IRC. We reviewed the medical record for patients (<21 years old) evaluated for a primary diagnosis of IRC between 1975 and 2013 at our institution. Demographic, clinical, echocardiographic, and catheterization data were abstracted. The patients were divided into 2 groups comprising a historical cohort (HC) (diagnosis: 1975 to 1993, n = 8) and a contemporary cohort (CC) (diagnosis: 1994 to 2013, n = 12). Twenty children were identified with IRC (mean age at presentation 9.7 ± 6.5 years, 55% female). Mean length of follow-up was 6.5 ± 8.4 years (range 0.1 to 35.6 years). In the CC, 7 of 12 patients (58%) progressed to cardiac transplantation (mean age of 9 ± 4 years at transplant, mean interval from diagnosis of IRC: 1.5 ± 0.9 years). Overall survival was improved significantly in the CC compared with the HC (80% vs. 38%, p = 0.02), but transplantation free survival was no different between the CC and HC over 5 years (38% vs 38%, p = 0.65). In the CC, elevation of mitral valve Doppler E/e' ratio on echocardiography was associated with increased mortality (p = 0.01). In conclusion, IRC continues has a poor prognosis. Early referral for transplantation was associated with improved overall survival in the modern era. Patients with markedly elevated E/e' ratio may have increased risk of death.
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http://dx.doi.org/10.1016/j.amjcard.2018.01.045DOI Listing
May 2018

Pediatric Dilated Cardiomyopathy-Associated (Leucine-Rich Repeat-Containing 10) Variant Reveals LRRC10 as an Auxiliary Subunit of Cardiac L-Type Ca Channels.

J Am Heart Assoc 2018 02 3;7(3). Epub 2018 Feb 3.

Cellular and Molecular Arrhythmia Research Program, University of Wisconsin-Madison, Madison, WI

Background: Genetic causes of dilated cardiomyopathy (DCM) are incompletely understood. LRRC10 (leucine-rich repeat-containing 10) is a cardiac-specific protein of unknown function. Heterozygous mutations in have been suggested to cause DCM, and deletion of in mice results in DCM.

Methods And Results: Whole-exome sequencing was carried out on a patient who presented at 6 weeks of age with DCM and her unaffected parents, filtering for rare, deleterious, recessive, and de novo variants. Whole-exome sequencing followed by trio-based filtering identified a homozygous recessive variant in , I195T. Coexpression of I195T with the L-type Ca channel (Ca1.2, β, and αδ subunits) in HEK293 cells resulted in a significant ≈0.5-fold decrease in I at 0 mV, in contrast to the ≈1.4-fold increase in I by coexpression of (n=9-12, <0.05). Coexpression of or I195T did not alter the surface membrane expression of Ca1.2. coexpression with Ca1.2 in the absence of auxiliary β and αδ subunits revealed coassociation of Ca1.2 and LRRC10 and a hyperpolarizing shift in the voltage dependence of activation (n=6-9, <0.05). Ventricular myocytes from mice had significantly smaller I, and coimmunoprecipitation experiments confirmed association between LRRC10 and the Ca1.2 subunit in mouse hearts.

Conclusions: Examination of a patient with DCM revealed homozygosity for a previously unreported variant: I195T. Wild-type and I195T LRRC10 function as cardiac-specific subunits of L-type Ca channels and exert dramatically different effects on channel gating, providing a potential link to DCM.
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http://dx.doi.org/10.1161/JAHA.117.006428DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5850229PMC
February 2018

Diagnostic Yield of Whole Exome Sequencing in Pediatric Dilated Cardiomyopathy.

J Cardiovasc Dev Dis 2017 Aug 8;4(3). Epub 2017 Aug 8.

Division of Pediatric Cardiology, Department of Pediatric and Adolescent Medicine, Mayo Clinic, Rochester, MN 55905, USA.

Dilated cardiomyopathy (DCM) is a heritable, genetically heterogeneous disorder characterized by progressive heart failure. DCM typically remains clinically silent until adulthood, yet symptomatic disease can develop in childhood. We sought to identify the genetic basis of pediatric DCM in 15 sporadic and three affected-siblings cases, comprised of 21 affected children (mean age, five years) whose parents had normal echocardiograms (mean age, 39 years). Twelve underwent cardiac transplantation and five died with severe heart failure. Parent-offspring whole exome sequencing (WES) data were filtered for rare, deleterious, de novo and recessive variants. In prior work, we reported de novo mutations in and and compound heterozygous mutations in and among four cases in our cohort. Here, de novo mutations in established DCM genes-, and -were identified among five additional cases. The mutation was previously reported in familial DCM. An identical unreported mutation was identified in two unrelated cases, both harboring gene-specific defects in cardiomyocyte nuclear morphology. Collectively, WES had a 50% diagnostic yield in our cohort, providing an explanation for pediatric heart failure and enabling informed family planning. Research is ongoing to discover novel DCM genes among the remaining families.
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http://dx.doi.org/10.3390/jcdd4030011DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5715713PMC
August 2017

Characteristic Morphologies of the Bicuspid Aortic Valve in Patients with Genetic Syndromes.

J Am Soc Echocardiogr 2018 02 28;31(2):194-200. Epub 2017 Nov 28.

Department of Pediatrics/Division of Pediatric Cardiology, Mayo Clinic, Rochester, Minnesota; Department of Medicine/Department of Cardiovascular Diseases, Mayo Clinic, Rochester, Minnesota. Electronic address:

Background: In patients with bicuspid aortic valve (BAV), complications including progressive aortic stenosis and aortic dilatation develop over time. The morphology of cusp fusion is one of the determinants of the type and severity of these complications. We present the association of morphology of cusp fusion in BAV patients with distinctive genetic syndromes.

Methods: The Mayo Clinic echocardiography database was retrospectively reviewed to identify patients (age ≤ 22 years) diagnosed with BAV from 1990 to 2016. Cusp fusion morphology was determined from the echocardiographic studies, while coexisting cardiac defects and genetic syndromes were determined from chart review.

Results: A total of 1,037 patients with BAV were identified: 550 (53%) had an isolated BAV, 299 (29%) had BAV and a coexisting congenital heart defect, and 188 (18%) had BAV and a coexisting genetic syndrome or disorder. There were no differences in distribution of morphology across the three groups. However, right-noncoronary (RN) cusp fusion was the predominant morphology associated with Down syndrome (P = .002) and right-left (RL) cusp fusion was the predominant morphology associated with Turner syndrome (P = .02), DiGeorge syndrome (P = .02), and Shone syndrome (P = .0007), when compared with valve morphology in patients with isolated BAV. Isolated BAV patients with RN cusp fusion had larger ascending aorta diameter (P = .001) and higher number of patients with ≥ moderate aortic regurgitation (P = .02), while those with RL cusp fusion had larger sinus of Valsalva diameter (P = .0006).

Conclusions: Morphological subtypes of BAV are associated with different genetic syndromes, suggesting distinct perturbations of developmental pathways in aortic valve malformation.
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http://dx.doi.org/10.1016/j.echo.2017.10.008DOI Listing
February 2018

Recessive TAF1A mutations reveal ribosomopathy in siblings with end-stage pediatric dilated cardiomyopathy.

Hum Mol Genet 2017 08;26(15):2874-2881

Cardiovascular Genetics Research Laboratory.

Non-ischemic dilated cardiomyopathy (DCM) has been recognized as a heritable disorder for over 25 years, yet clinical genetic testing is non-diagnostic in >50% of patients, underscoring the ongoing need for DCM gene discovery. Here, whole exome sequencing uncovered a novel molecular basis for idiopathic end-stage heart failure in two sisters who underwent cardiac transplantation at three years of age. Compound heterozygous recessive mutations in TAF1A, encoding an RNA polymerase I complex protein, were associated with marked fibrosis of explanted hearts and gene-specific nucleolar segregation defects in cardiomyocytes, indicative of impaired ribosomal RNA synthesis. Knockout of the homologous gene in zebrafish recapitulated a heart failure phenotype with pericardial edema, decreased ventricular systolic function, and embryonic mortality. These findings expand the clinical spectrum of ribosomopathies to include pediatric DCM.
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http://dx.doi.org/10.1093/hmg/ddx169DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6455043PMC
August 2017

gsSKAT: Rapid gene set analysis and multiple testing correction for rare-variant association studies using weighted linear kernels.

Genet Epidemiol 2017 05 16;41(4):297-308. Epub 2017 Feb 16.

Division of Biomedical Statistics and Informatics, Department of Health Sciences Research, Mayo Clinic, Rochester, Minnesota, United States of America.

Next-generation sequencing technologies have afforded unprecedented characterization of low-frequency and rare genetic variation. Due to low power for single-variant testing, aggregative methods are commonly used to combine observed rare variation within a single gene. Causal variation may also aggregate across multiple genes within relevant biomolecular pathways. Kernel-machine regression and adaptive testing methods for aggregative rare-variant association testing have been demonstrated to be powerful approaches for pathway-level analysis, although these methods tend to be computationally intensive at high-variant dimensionality and require access to complete data. An additional analytical issue in scans of large pathway definition sets is multiple testing correction. Gene set definitions may exhibit substantial genic overlap, and the impact of the resultant correlation in test statistics on Type I error rate control for large agnostic gene set scans has not been fully explored. Herein, we first outline a statistical strategy for aggregative rare-variant analysis using component gene-level linear kernel score test summary statistics as well as derive simple estimators of the effective number of tests for family-wise error rate control. We then conduct extensive simulation studies to characterize the behavior of our approach relative to direct application of kernel and adaptive methods under a variety of conditions. We also apply our method to two case-control studies, respectively, evaluating rare variation in hereditary prostate cancer and schizophrenia. Finally, we provide open-source R code for public use to facilitate easy application of our methods to existing rare-variant analysis results.
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http://dx.doi.org/10.1002/gepi.22036DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5397327PMC
May 2017

A breakthrough in spontaneous coronary artery dissection pathogenesis: is it an inherited condition?

Expert Rev Cardiovasc Ther 2017 01 14;15(1):1-2. Epub 2016 Dec 14.

b Department of Cardiovascular Diseases , Mayo Clinic , Rochester MN , USA.

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http://dx.doi.org/10.1080/14779072.2017.1266254DOI Listing
January 2017

A modifier screen identifies as a cardiomyopathy susceptibility gene.

JCI Insight 2016 Sep;1(14)

Department of Biochemistry and Molecular Biology, Mayo Clinic, Rochester, Minnesota, USA; Division of Cardiovascular Diseases, Mayo Clinic, Rochester, Minnesota, USA.

Mutagenesis screening is a powerful forward genetic approach that has been successfully applied in lower-model organisms to discover genetic factors for biological processes. This phenotype-based approach has yet to be established in vertebrates for probing major human diseases, largely because of the complexity of colony management. Herein, we report a rapid strategy for identifying genetic modifiers of cardiomyopathy (CM). Based on the application of doxorubicin stress to zebrafish insertional cardiac (ZIC) mutants, we identified 4 candidate CM-modifying genes, of which 3 have been linked previously to CM. The long isoform of DnaJ (Hsp40) homolog, subfamily B, member 6b () was identified as a CM susceptibility gene, supported by identification of rare variants in its human ortholog from CM patients. Mechanistic studies indicated that the deleterious, loss-of-function modifying effects of can be ameliorated by inhibition of ER stress. In contrast, overexpression of exerts cardioprotective effects on both fish and mouse CM models. Together, our findings establish a mutagenesis screening strategy that is scalable for systematic identification of genetic modifiers of CM, feasible to suggest therapeutic targets, and expandable to other major human diseases.
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http://dx.doi.org/10.1172/jci.insight.88797DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5023154PMC
September 2016

Post hoc Analysis for Detecting Individual Rare Variant Risk Associations Using Probit Regression Bayesian Variable Selection Methods in Case-Control Sequencing Studies.

Genet Epidemiol 2016 09 17;40(6):461-9. Epub 2016 Jun 17.

Division of Biomedical Statistics and Informatics, Department of Health Sciences Research, Mayo Clinic, Rochester, Minnesota, United States of America.

Rare variants (RVs) have been shown to be significant contributors to complex disease risk. By definition, these variants have very low minor allele frequencies and traditional single-marker methods for statistical analysis are underpowered for typical sequencing study sample sizes. Multimarker burden-type approaches attempt to identify aggregation of RVs across case-control status by analyzing relatively small partitions of the genome, such as genes. However, it is generally the case that the aggregative measure would be a mixture of causal and neutral variants, and these omnibus tests do not directly provide any indication of which RVs may be driving a given association. Recently, Bayesian variable selection approaches have been proposed to identify RV associations from a large set of RVs under consideration. Although these approaches have been shown to be powerful at detecting associations at the RV level, there are often computational limitations on the total quantity of RVs under consideration and compromises are necessary for large-scale application. Here, we propose a computationally efficient alternative formulation of this method using a probit regression approach specifically capable of simultaneously analyzing hundreds to thousands of RVs. We evaluate our approach to detect causal variation on simulated data and examine sensitivity and specificity in instances of high RV dimensionality as well as apply it to pathway-level RV analysis results from a prostate cancer (PC) risk case-control sequencing study. Finally, we discuss potential extensions and future directions of this work.
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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5063501PMC
http://dx.doi.org/10.1002/gepi.21983DOI Listing
September 2016

De novo RRAGC mutation activates mTORC1 signaling in syndromic fetal dilated cardiomyopathy.

Hum Genet 2016 08 27;135(8):909-917. Epub 2016 May 27.

Cardiovascular Genetics Research Laboratory, Mayo Clinic, Rochester MN.

Idiopathic dilated cardiomyopathy (DCM) is a heritable, genetically heterogeneous disorder with variable age-dependent penetrance. We sought to identify the genetic underpinnings of syndromic, sporadic DCM in a newborn female diagnosed in utero. Postnatal evaluation revealed ventricular dilation and systolic dysfunction, bilateral cataracts, and mild facial dysmorphisms. Comprehensive metabolic and genetic testing, including chromosomal microarray, mitochondrial DNA and targeted RASopathy gene sequencing, and clinical whole exome sequencing for known cardiomyopathy genes was non-diagnostic. Following exclusion of asymptomatic DCM in the parents, trio-based whole exome sequencing was carried out on a research basis, filtering for rare, predicted deleterious de novo and recessive variants. An unreported de novo S75Y mutation was discovered in RRAGC, encoding Ras-related GTP binding C, an essential GTPase in nutrient-activated mechanistic target of rapamycin complex 1 (mTORC1) signaling. In silico protein modeling and molecular dynamics simulation predicted the mutation to disrupt ligand interactions and increase the GDP-bound state. Overexpression of RagC(S75Y) rendered AD293 cells partially insensitive to amino acid deprivation, resulting in increased mTORC1 signaling compared to wild-type RagC. These findings implicate mTORC1 dysregulation through a gain-of-function mutation in RagC as a novel molecular basis for syndromic forms of pediatric heart failure, and expand genotype-phenotype correlation in RASopathy-related syndromes.
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http://dx.doi.org/10.1007/s00439-016-1685-3DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4947566PMC
August 2016

Ebstein anomaly, left ventricular non-compaction, and early onset heart failure associated with a de novo α-tropomyosin gene mutation.

Am J Med Genet A 2016 08 13;170(8):2186-90. Epub 2016 May 13.

Division of Pediatric Cardiology, Department of Pediatric and Adolescent Medicine, Mayo Clinic, Rochester, Minnesota.

Ebstein anomaly of the tricuspid valve (EA) can be associated with left ventricular non-compaction (LVNC), a rare congenital cardiomyopathy. We report a 2 year-old female with EA and severe tricuspid regurgitation, LVNC, pulmonary hypertension, and chronic biventricular systolic heart failure, who died during evaluation for cardiac transplantation. Gene panel testing revealed a heterozygous de novo missense mutation in TPM1, which encodes the cardiac sarcomeric thin filament protein α-tropomyosin. The c.475G>A variant results in a p.Asp159Asn substitution, altering a highly conserved residue predicted to be damaging to protein structure and function. TPM1 is the second gene linked to EA with LVNC in humans, implicating overlap in the molecular basis of structural and myopathic heart disease. © 2016 Wiley Periodicals, Inc.
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http://dx.doi.org/10.1002/ajmg.a.37745DOI Listing
August 2016

Modeling -Associated Dilated Cardiomyopathy in Adult Zebrafish.

J Cardiovasc Dev Dis 2016 Mar 26;3(1). Epub 2016 Jan 26.

Department of Biochemistry and Molecular Biology, Mayo Clinic College of Medicine, 200 First St. SW Rochester, MN 55905, USA.

Animal models have played a critical role in validating human dilated cardiomyopathy (DCM) genes, particularly those that implicate novel mechanisms for heart failure. However, the disease phenotype may be delayed due to age-dependent penetrance. For this reason, we generated an adult zebrafish model, which is a simpler vertebrate model with higher throughput than rodents. Specifically, we studied the zebrafish homologue of , a recently identified gene for adult-onset autosomal recessive DCM. We showed cardiac expression of transcripts, by whole mount hybridization in zebrafish embryos, and demonstrated nuclear and sarcomeric I-band subcellular localization of Gatad1 protein in cardiomyocytes, by injecting a Tol2 plasmid encoding fluorescently-tagged Gatad1. We next generated knock-out fish lines by TALEN technology and a transgenic fish line that expresses the human DCM -S102P mutation in cardiomyocytes. Under stress conditions, longitudinal studies uncovered heart failure (HF)-like phenotypes in stable KO mutants and a tendency toward HF phenotypes in transgenic lines. Based on these efforts of studying a gene-based inherited cardiomyopathy model, we discuss the strengths and bottlenecks of adult zebrafish as a new vertebrate model for assessing candidate cardiomyopathy genes.
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http://dx.doi.org/10.3390/jcdd3010006DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5611887PMC
March 2016

Spontaneous coronary artery dissection and its association with heritable connective tissue disorders.

Heart 2016 06 10;102(11):876-81. Epub 2016 Feb 10.

Department of Internal Medicine, Mayo Clinic, Rochester, Minnesota, USA Division of Cardiovascular Diseases, Mayo Clinic, Rochester, Minnesota, USA.

Objective: Spontaneous coronary artery dissection (SCAD) is an under-recognised but important cause of myocardial infarction and sudden cardiac death. We sought to determine the role of medical and molecular genetic screening for connective tissue disorders in patients with SCAD.

Methods: We performed a single-centre retrospective descriptive analysis of patients with spontaneous coronary artery disease who had undergone medical genetics evaluation 1984-2014 (n=116). The presence or absence of traits suggestive of heritable connective tissue disease was extracted. Genetic testing for connective tissue disorders and/or aortopathies, if performed, is also reported.

Results: Of the 116 patients (mean age 44.2 years, 94.8% women and 41.4% with non-coronary fibromuscular dysplasia (FMD)), 59 patients underwent genetic testing, of whom 3 (5.1%) received a diagnosis of connective tissue disorder: a 50-year-old man with Marfan syndrome; a 43-year-old woman with vascular Ehlers-Danlos syndrome and FMD; and a 45-year-old woman with vascular Ehlers-Danlos syndrome. An additional 12 patients (20.3%) had variants of unknown significance, none of which was thought to be a definite disease-causing mutation based on in silico analyses.

Conclusions: Only a minority of patients with SCAD who undergo genetic evaluation have a likely pathogenic mutation identified on gene panel testing. Even fewer exhibit clinical features of connective tissue disorder. These findings underscore the need for further studies to elucidate the molecular mechanisms of SCAD.
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http://dx.doi.org/10.1136/heartjnl-2015-308645DOI Listing
June 2016

Exome Sequencing Identifies Pathogenic and Modifier Mutations in a Child With Sporadic Dilated Cardiomyopathy.

J Am Heart Assoc 2015 Dec 9;4(12). Epub 2015 Dec 9.

Cardiovascular Genetics Research Laboratory, Mayo Clinic, Rochester, MN (P.A.L., T.M.O.) Division of Pediatric Cardiology, Department of Pediatric and Adolescent Medicine, Mayo Clinic, Rochester, MN (T.M.O.) Division of Cardiovascular Diseases, Department of Internal Medicine, Mayo Clinic, Rochester, MN (T.M.O.).

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 TNNT2 was identified, previously reported and functionally validated in familial DCM with markedly variable penetrance. Additionally, recessive compound heterozygous truncating mutations were identified in XIRP2, 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 ICDs, findings similar to Xirp2(-/-) mice.

Conclusions: The synergistic effects of TNNT2 and XIRP2 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 XIRP2 as a novel modifier gene in the pathogenesis of DCM.
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http://dx.doi.org/10.1161/JAHA.115.002443DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4845292PMC
December 2015

LRRC10 is required to maintain cardiac function in response to pressure overload.

Am J Physiol Heart Circ Physiol 2016 Jan 25;310(2):H269-78. Epub 2015 Nov 25.

Department of Cell and Regenerative Biology, School of Medicine and Public Health, University of Wisconsin, Madison, Wisconsin; Molecular and Environmental Toxicology Center, School of Medicine and Public Health, University of Wisconsin, Madison, Wisconsin;

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 His(150) of 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.
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http://dx.doi.org/10.1152/ajpheart.00717.2014DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4747898PMC
January 2016

Modeling structural and functional deficiencies of RBM20 familial dilated cardiomyopathy using human induced pluripotent stem cells.

Hum Mol Genet 2016 Jan 24;25(2):254-65. Epub 2015 Nov 24.

Center for Regenerative Medicine, Division of General Internal Medicine, Department of Molecular Pharmacology and Experimental Therapeutics, Division of Pediatric Cardiology, Transplant Center, Mayo Clinic, Rochester, MN 55905, USA and

Dilated cardiomyopathy (DCM) is a leading cause of heart failure. In families with autosomal-dominant DCM, heterozygous missense mutations were identified in RNA-binding motif protein 20 (RBM20), a spliceosome protein induced during early cardiogenesis. Dermal fibroblasts from two unrelated patients harboring an RBM20 R636S missense mutation were reprogrammed to human induced pluripotent stem cells (hiPSCs) and differentiated to beating cardiomyocytes (CMs). Stage-specific transcriptome profiling identified differentially expressed genes ranging from angiogenesis regulator to embryonic heart transcription factor as initial molecular aberrations. Furthermore, gene expression analysis for RBM20-dependent splice variants affected sarcomeric (TTN and LDB3) and calcium (Ca(2+)) handling (CAMK2D and CACNA1C) genes. Indeed, RBM20 hiPSC-CMs exhibited increased sarcomeric length (RBM20: 1.747 ± 0.238 µm versus control: 1.404 ± 0.194 µm; P < 0.0001) and decreased sarcomeric width (RBM20: 0.791 ± 0.609 µm versus control: 0.943 ± 0.166 µm; P < 0.0001). Additionally, CMs showed defective Ca(2+) handling machinery with prolonged Ca(2+) levels in the cytoplasm as measured by greater area under the curve (RBM20: 814.718 ± 94.343 AU versus control: 206.941 ± 22.417 AU; P < 0.05) and higher Ca(2+) spike amplitude (RBM20: 35.281 ± 4.060 AU versus control:18.484 ± 1.518 AU; P < 0.05). β-adrenergic stress induced with 10 µm norepinephrine demonstrated increased susceptibility to sarcomeric disorganization (RBM20: 86 ± 10.5% versus control: 40 ± 7%; P < 0.001). This study features the first hiPSC model of RBM20 familial DCM. By monitoring human cardiac disease according to stage-specific cardiogenesis, this study demonstrates RBM20 familial DCM is a developmental disorder initiated by molecular defects that pattern maladaptive cellular mechanisms of pathological cardiac remodeling. Indeed, hiPSC-CMs recapitulate RBM20 familial DCM phenotype in a dish and establish a tool to dissect disease-relevant defects in RBM20 splicing as a global regulator of heart function.
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http://dx.doi.org/10.1093/hmg/ddv468DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4706113PMC
January 2016

Familial Incidence of Cardiovascular Malformations in Hypoplastic Left Heart Syndrome.

Am J Cardiol 2015 Dec 10;116(11):1762-6. Epub 2015 Sep 10.

Division of Pediatric Cardiology, Department of Pediatric and Adolescent Medicine, Mayo Clinic, Rochester, Minnesota; Division of Cardiovascular Diseases, Department of Internal Medicine, Mayo Clinic, Rochester, Minnesota.

Obstructive left-sided congenital heart lesions exhibit familial clustering, and familial echocardiographic screening for bicuspid aortic valve has become standard practice. Hypoplastic left heart syndrome (HLHS) is a severe left-sided obstructive lesion; however, familial screening is not universally recommended. The purpose of this study was to define the incidence of cardiovascular malformations (CVMs) in first-degree relatives of HLHS probands. First-degree relatives were screened for CVM by transthoracic echocardiography. Screening was completed in 152 family members (97 parents and 55 siblings) of 52 probands. Of these, 17 of 152 (11%) had CVM. Anomalies detected included: bicuspid aortic valve in 5 (3%), isolated dilated ascending aorta in 4 (3%), coarctation of the aorta in 1, partial anomalous pulmonary venous connection in 1, anomalous, intramural coronary artery in 1, bicuspid pulmonary valve in 1, and other anomalies in 4. Most were previously undiagnosed (11 of 17, 65%). Fourteen of 52 families (27%) had ≥1 relative with CVM. Overall, 7 of 55 siblings (13%), 5 of 46 fathers (11%) and 5 of 51 mothers (10%) had CVM. Although the incidence of CVM in first-degree relatives of HLHS probands was lower in this cohort than previously reported, it remained substantial, with at least one additional member having CVM in 27% of families. The frequent occurrence of undiagnosed CVM highlights the importance of routine familial screening in HLHS. In fact, even if screening was done in childhood, it may be appropriate to screen again in the third or fourth decade to exclude isolated enlargement of the ascending aorta.
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http://dx.doi.org/10.1016/j.amjcard.2015.08.045DOI Listing
December 2015

Compound heterozygous NOTCH1 mutations underlie impaired cardiogenesis in a patient with hypoplastic left heart syndrome.

Hum Genet 2015 Sep 12;134(9):1003-11. Epub 2015 Jul 12.

Cardiovascular Genetics Research Laboratory, Mayo Clinic, 200 First Street SW, Rochester, MN, 55905, USA.

Hypoplastic left heart syndrome (HLHS) is a severe congenital heart defect (CHD) that necessitates staged, single ventricle surgical palliation. An increased frequency of bicuspid aortic valve (BAV) has been observed among relatives. We postulated number of mutant alleles as a molecular basis for variable CHD expression in an extended family comprised of an HLHS proband and four family members who underwent echocardiography and whole-genome sequencing (WGS). Dermal fibroblast-derived induced pluripotent stem cells (iPSC) were procured from the proband-parent trio and bioengineered into cardiomyocytes. Cardiac phenotyping revealed aortic valve atresia and a slit-like left ventricular cavity in the HLHS proband, isolated bicuspid pulmonary valve in his mother, BAV in a maternal 4° relative, and no CHD in his father or sister. Filtering of WGS for rare, functional variants that segregated with CHD and were compound heterozygous in the HLHS proband identified NOTCH1 as the sole candidate gene. An unreported missense mutation (P1964L) in the cytoplasmic domain, segregating with semilunar valve malformation, was maternally inherited and a rare missense mutation (P1256L) in the extracellular domain, clinically silent in the heterozygous state, was paternally inherited. Patient-specific iPSCs exhibited diminished transcript levels of NOTCH1 signaling pathway components, impaired myocardiogenesis, and a higher prevalence of heterogeneous myofilament organization. Extended, phenotypically characterized families enable WGS-derived variant filtering for plausible Mendelian modes of inheritance, a powerful strategy to discover molecular underpinnings of CHD. Identification of compound heterozygous NOTCH1 mutations and iPSC-based functional modeling implicate mutant allele burden and impaired myogenic potential as mechanisms for HLHS.
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http://dx.doi.org/10.1007/s00439-015-1582-1DOI Listing
September 2015

Recessive MYH6 Mutations in Hypoplastic Left Heart With Reduced Ejection Fraction.

Circ Cardiovasc Genet 2015 Aug 17;8(4):564-71. Epub 2015 Jun 17.

From the Cardiovascular Genetics Research Laboratory (J.L.T., T.M.O.), Division of Pediatric Cardiology, Department of Pediatric and Adolescent Medicine (M.Y.Q., P.W.O'L., T.M.O.), Division of Cardiovascular Diseases, Department of Internal Medicine (T.M.O.), Departments of Health Sciences Research and Biomedical Statistics and Informatics (M.T.Z., J.M.E.), Medical Genome Facility (B.W.E., E.D.W.), and Department of Biochemistry and Molecular Biology (E.D.W.), Mayo Clinic, Rochester, MN.

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.
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http://dx.doi.org/10.1161/CIRCGENETICS.115.001070DOI Listing
August 2015