Sara M. Fitzgerald-Butt

NOTCH1 mutations in individuals with left ventricular outflow tract malformations reduce ligand-induced signaling

Congenital aortic valve stenosis (AVS), coarctation of the aorta (COA) and hypoplastic left heart syndrome (HLHS) are congenital cardiovascular malformations that all involve the left ventricular outflow tract (LVOT). They are presumably caused by a similar developmental mechanism involving the developing endothelium. The exact etiology for most LVOT malformations is unknown, but a strong genetic component has been established. We demonstrate here that mutations in the gene NOTCH1, coding for a receptor in a developmentally important signaling pathway, are found across the spectrum of LVOT defects. We identify two specific mutations that reduce ligand (JAGGED1) induced NOTCH1 signaling. One of these mutations perturbs the S1 cleavage of the receptor in the Golgi. These findings suggest that the levels of NOTCH1 signaling are tightly regulated during cardiovascular development, and that relatively minor alterations may promote LVOT defects. These results also establish for the first time that AVS, COA and HLHS can share a common pathogenetic mechanism at the molecular level, explaining observations of these defects co-occurring within families.

Linkage analysis of left ventricular outflow tract malformations (aortic valve stenosis, coarctation of the aorta, and hypoplastic left heart syndrome).

The left ventricular outflow tract (LVOT) malformations aortic valve stenosis (AVS), coarctation of the aorta (CoA), and hypoplastic left heart syndrome (HLHS) are significant causes of infant mortality. These three malformations are thought to share developmental pathogenetic mechanisms. A strong genetic component has been demonstrated earlier, but the underlying genetic etiologies are unknown. Our objective was to identify genetic susceptibility loci for the broad phenotype of LVOT malformations. We genotyped 411 microsatellites spaced at an average of 10 cM in 43 families constituting 289 individuals, with an additional 5 cM spaced markers for fine mapping. A non-parametric linkage (NPL) analysis of the combined LVOT malformations gave three suggestive linkage peaks on chromosomes 16p12 (NPL score (NPLS)=2.52), 2p23 (NPLS=2.41), and 10q21 (NPLS=2.14). Individually, suggestive peaks for AVS families occurred on chromosomes 16p12 (NPLS=2.64), 7q36 (NPLS=2.31), and 2p25 (NPLS=2.14); and for CoA families on chromosome 1q24 (NPLS=2.61), 6p23 (NPLS=2.29), 7p14 (NPLS=2.27), 10q11 (NPLS=1.98), and 2p15 (NPLS=2.02). Significant NPLS in HLHS families were noted for chromosome 2p15 (NPLS=3.23), with additional suggestive peaks on 19q13 (NPLS=2.16) and 10q21 (NPLS=2.07). Overlapping linkage signals on 10q11 (AVS and CoA) and 16p12 (AVS, CoA, and HLHS) led to higher NPL scores when all malformations were analyzed together. In conclusion, we report suggestive evidence for linkage to chromosomes 2p23, 10q21, and 16p12 for the LVOT malformations of AVS, CoA, and HLHS individually and in a combined analysis, with a significant peak on 2p15 for HLHS. Overlapping linkage peaks provide evidence for a common genetic etiology.

Rare GATA5 sequence variants identified in individuals with bicuspid aortic valve

Background:Bicuspid aortic valve (BAV) is the most common type of congenital heart disease (CHD) and has a proposed genetic etiology. BAV is categorized by cusp fusion, with right-left (R-L) cusp fusion being associated with additional CHD, and right-noncoronary cusp (R-NC) fusion being associated with aortic valve dysfunction. Loss of murine Gata5, which encodes a cardiac transcription factor, results in a partially penetrant R-NC BAV, and we hypothesize that mutations in GATA5 are associated with R-NC BAV in humans.Methods:A cohort of 78 BAV patients (50 with isolated BAV and 28 with associated aortic coarctation) was analyzed using Sanger sequencing to identify GATA5 sequence variants. Biochemical assays were performed to identify functional deficits of identified sequence variants.Results:We identified two rare heterozygous nonsynonymous variants, p.Gln3Arg and p.Leu233Pro, for a frequency of 2.6% (2/78). Both individuals with nonsynonymous variants had BAV and aortic coarctation, one R-L and one R-NC subtype. Of the nonsynonymous variants, only p.Gln3Arg demonstrated decreased transcriptional activity in vitro.Conclusion:Rare sequence variants in GATA5 are associated with human BAV. Our findings suggest a genotype–phenotype correlation in regards to associated CHD but not cusp fusion.

Association of common variants in ERBB4 with congenital left ventricular outflow tract obstruction defects

BACKGROUND The left ventricular outflow tract (LVOT) defects aortic valve stenosis (AVS), coarctation of the aorta (COA), and hypoplastic left heart syndrome (HLHS) represent an embryologically related group of congenital cardiovascular malformations. They are common and cause substantial morbidity and mortality. Prior evidence suggests a strong genetic component in their causation. METHODS We selected NRG1, ERBB3, and ERBB4 of the epidermal growth factor receptor (EGFR) signaling pathway as candidate genes for investigation of association with LVOT defects based on the importance of this pathway in cardiac development and the phenotypes in knockout mouse models. Single nucleotide polymorphism (SNP) genotyping was performed on 343 affected case-parent trios of European ancestry. RESULTS We identified a specific haplotype in intron 3 of ERBB4 that was positively associated with the combined LVOT defects phenotype (p=0.0005) and in each anatomic defect AVS, COA, and HLHS separately. Mutation screening of individuals with an LVOT defect failed to identify a coding sequence or splice site change in ERBB4. RT-PCR on lymphoblastoid cells from LVOT subjects did not show altered splice variant ratios among those homozygous for the associated haplotype. CONCLUSION These results suggest ERBB4 is associated with LVOT defects. Further replication will be required in separate cohorts to confirm the consistency of the observed association.

Use of a targeted, combinatorial next-generation sequencing approach for the study of bicuspid aortic valve

BackgroundBicuspid aortic valve (BAV) is the most common type of congenital heart disease with a population prevalence of 1-2%. While BAV is known to be highly heritable, mutations in single genes (such as GATA5 and NOTCH1) have been reported in few human BAV cases. Traditional gene sequencing methods are time and labor intensive, while next-generation high throughput sequencing remains costly for large patient cohorts and requires extensive bioinformatics processing. Here we describe an approach to targeted multi-gene sequencing with combinatorial pooling of samples from BAV patients.MethodsWe studied a previously described cohort of 78 unrelated subjects with echocardiogram-identified BAV. Subjects were identified as having isolated BAV or BAV associated with coarctation of aorta (BAV-CoA). BAV cusp fusion morphology was defined as right-left cusp fusion, right non-coronary cusp fusion, or left non-coronary cusp fusion. Samples were combined into 19 pools using a uniquely overlapping combinatorial design; a given mutation could be attributed to a single individual on the basis of which pools contained the mutation. A custom gene capture of 97 candidate genes was sequenced on the Illumina HiSeq 2000. Multistep bioinformatics processing was performed for base calling, variant identification, and in-silico analysis of putative disease-causing variants.ResultsTargeted capture identified 42 rare, non-synonymous, exonic variants involving 35 of the 97 candidate genes. Among these variants, in-silico analysis classified 33 of these variants as putative disease-causing changes. Sanger sequencing confirmed thirty-one of these variants, found among 16 individuals. There were no significant differences in variant burden among BAV fusion phenotypes or isolated BAV versus BAV-CoA. Pathway analysis suggests a role for the WNT signaling pathway in human BAV.ConclusionWe successfully developed a pooling and targeted capture strategy that enabled rapid and cost effective next generation sequencing of target genes in a large patient cohort. This approach identified a large number of putative disease-causing variants in a cohort of patients with BAV, including variants in 26 genes not previously associated with human BAV. The data suggest that BAV heritability is complex and polygenic. Our pooling approach saved over

Understanding of informed consent by parents of children enrolled in a genetic biobank

39,350 compared to an unpooled, targeted capture sequencing strategy.

Utilization of Whole Exome Sequencing to Identify Causative Mutations in Familial Congenital Heart Disease

Purpose:Prior research suggests that parents undervalue long-term risks associated with their children’s participation in research studies. The primary aim of this study was to evaluate parental understanding of informed consent for a pediatric biobanking study.Methods:The study population included parents who provided consent for their child to participate in a study examining the genetic etiology of congenital cardiovascular malformations. Informed consent understanding was measured by adapting the Quality of Informed Consent assessment to our study. We evaluated possible predictors of individual Quality of Informed Consent items using generalized estimating equations.Results:A total of 252 individuals representing 188 families completed the study. The Quality of Informed Consent items best understood by parents included consent to participate in research, the main purpose of the study, and the possibility of no direct benefit. The items least understood by parents were those involving the indefinite storage of DNA, the possible risks of participation, and the fact that the study was not intended to treat their child’s heart defect. Parent age and medical decision making by one versus both parents were frequent predictors of individual Quality of Informed Consent items.Conclusion:Parents overestimate personal benefit and underestimate the risks associated with their child’s participation in a biobanking study.Genet Med 16 2, 141–148.

Novel familial dilated cardiomyopathy mutation in MYL2 affects the structure and function of myosin regulatory light chain

Background—Congenital heart disease (CHD) is the most common type of birth defect with family- and population-based studies supporting a strong genetic cause for CHD. The goal of this study was to determine whether a whole exome sequencing (WES) approach could identify pathogenic-segregating variants in multiplex CHD families. Methods and Results—WES was performed on 9 kindreds with familial CHD, 4 with atrial septal defects, 2 with patent ductus arteriosus, 2 with tetralogy of Fallot, and 1 with pulmonary valve dysplasia. Rare variants (<1% minor allele frequency) that segregated with disease were identified by WES, and variants in 69 CHD candidate genes were further analyzed. These selected variants were subjected to in silico analysis to predict pathogenicity and resulted in the discovery of likely pathogenic mutations in 3 of 9 (33%) families. A GATA4 mutation in the transactivation domain, p.G115W, was identified in familial atrial septal defects and demonstrated decreased transactivation ability in vitro. A p.I263V mutation in TLL1 was identified in an atrial septal defects kindred and is predicted to affect the enzymatic functionality of TLL1. A disease-segregating splice donor site mutation in MYH11 (c.4599+1delG) was identified in familial patent ductus arteriosus and found to disrupt normal splicing of MYH11 mRNA in the affected individual. Conclusions—Our findings demonstrate the clinical utility of WES to identify causative mutations in familial CHD and demonstrate the successful use of a CHD candidate gene list to allow for a more streamlined approach enabling rapid prioritization and identification of likely pathogenic variants from large WES data sets. Clinical Trial Registration—URL: https://clinicaltrials.gov; Unique Identifier: NCT0112048.

Genetic knowledge and attitudes of parents of children with congenital heart defects.

Dilated cardiomyopathy (DCM) is a disease of the myocardium characterized by left ventricular dilatation and diminished contractile function. Here we describe a novel DCM mutation in the myosin regulatory light chain (RLC), in which aspartic acid at position 94 is replaced by alanine (D94A). The mutation was identified by exome sequencing of three adult first‐degree relatives who met formal criteria for idiopathic DCM. To obtain insight into the functional significance of this pathogenic MYL2 variant, we cloned and purified the human ventricular RLC wild‐type (WT) and D94A mutant proteins, and performed in vitro experiments using RLC‐mutant or WT‐reconstituted porcine cardiac preparations. The mutation induced a reduction in the α‐helical content of the RLC, and imposed intra‐molecular rearrangements. The phosphorylation of RLC by Ca2+/calmodulin‐activated myosin light chain kinase was not affected by D94A. The mutation was seen to impair binding of RLC to the myosin heavy chain, and its incorporation into RLC‐depleted porcine myosin. The actin‐activated ATPase activity of mutant‐reconstituted porcine cardiac myosin was significantly higher compared with ATPase of wild‐type. No changes in the myofibrillar ATPase–pCa relationship were observed in wild‐type‐ or D94A‐reconstituted preparations. Measurements of contractile force showed a slightly reduced maximal tension per cross‐section of muscle, with no change in the calcium sensitivity of force in D94A‐reconstituted skinned porcine papillary muscle strips compared with wild‐type. Our data indicate that subtle structural rearrangements in the RLC molecule, followed by its impaired interaction with the myosin heavy chain, may trigger functional abnormalities contributing to the DCM phenotype.

Assessment of large copy number variants in patients with apparently isolated congenital left-sided cardiac lesions reveals clinically relevant genomic events

Clinical genetic testing for specific isolated congenital heart defects (CHD) is becoming standard of care in pediatric cardiology practice. Both genetic knowledge and attitudes toward genetic testing are associated with an increased utilization of genetic testing, but these factors have not been evaluated in parents of children with CHD. We mailed a survey to measure the demographics, genetic knowledge, and attitudes towards genetic testing of parents of children with CHD who previously consented to participate in a separate research study of the genetic etiology of left ventricular outflow tract malformations (LVOT). Of the 378 eligible families, 190 (50%) returned surveys with both parents completing surveys in 97 (51%) families, resulting in 287 participants. Genetic knowledge was assessed on an adapted measure on which the mean percent correct was 73.8%. Educational attainment and household income were directly and significantly associated with genetic knowledge (P < 0.001). Attitudes about the health effects of genetic testing were favorable with at least 57% agreeing that genetic testing would be used for managing health care and finding cures for disease. Conversely, a minority of participants found it likely that genetic testing would be used for insurance (up to 39.9%), employment (15.8%), or racial/social discrimination (up to 11.2%). Parents of younger children were less likely to endorse employment or racial/social discrimination. Genetic knowledge was not correlated with specific attitudes. Among parents of children with CHD, genetic knowledge was directly associated with household income and education, but additional research is necessary to determine what factors influence attitudes towards genetic testing.