Maryse Thibeault

Rare Copy Number Variants Contribute to Congenital Left-Sided Heart Disease

Left-sided congenital heart disease (CHD) encompasses a spectrum of malformations that range from bicuspid aortic valve to hypoplastic left heart syndrome. It contributes significantly to infant mortality and has serious implications in adult cardiology. Although left-sided CHD is known to be highly heritable, the underlying genetic determinants are largely unidentified. In this study, we sought to determine the impact of structural genomic variation on left-sided CHD and compared multiplex families (464 individuals with 174 affecteds (37.5%) in 59 multiplex families and 8 trios) to 1,582 well-phenotyped controls. 73 unique inherited or de novo CNVs in 54 individuals were identified in the left-sided CHD cohort. After stringent filtering, our gene inventory reveals 25 new candidates for LS-CHD pathogenesis, such as SMC1A, MFAP4, and CTHRC1, and overlaps with several known syndromic loci. Conservative estimation examining the overlap of the prioritized gene content with CNVs present only in affected individuals in our cohort implies a strong effect for unique CNVs in at least 10% of left-sided CHD cases. Enrichment testing of gene content in all identified CNVs showed a significant association with angiogenesis. In this first family-based CNV study of left-sided CHD, we found that both co-segregating and de novo events associate with disease in a complex fashion at structural genomic level. Often viewed as an anatomically circumscript disease, a subset of left-sided CHD may in fact reflect more general genetic perturbations of angiogenesis and/or vascular biology.

Mutations in SGOL1 cause a novel cohesinopathy affecting heart and gut rhythm

The pacemaking activity of specialized tissues in the heart and gut results in lifelong rhythmic contractions. Here we describe a new syndrome characterized by Chronic Atrial and Intestinal Dysrhythmia, termed CAID syndrome, in 16 French Canadians and 1 Swede. We show that a single shared homozygous founder mutation in SGOL1, a component of the cohesin complex, causes CAID syndrome. Cultured dermal fibroblasts from affected individuals showed accelerated cell cycle progression, a higher rate of senescence and enhanced activation of TGF-β signaling. Karyotypes showed the typical railroad appearance of a centromeric cohesion defect. Tissues derived from affected individuals displayed pathological changes in both the enteric nervous system and smooth muscle. Morpholino-induced knockdown of sgol1 in zebrafish recapitulated the abnormalities seen in humans with CAID syndrome. Our findings identify CAID syndrome as a novel generalized dysrhythmia, suggesting a new role for SGOL1 and the cohesin complex in mediating the integrity of human cardiac and gut rhythm.

Family Based Whole Exome Sequencing Reveals the Multifaceted Role of Notch Signaling in Congenital Heart Disease

Left-ventricular outflow tract obstructions (LVOTO) encompass a wide spectrum of phenotypically heterogeneous heart malformations which frequently cluster in families. We performed family based whole-exome and targeted re-sequencing on 182 individuals from 51 families with multiple affected members. Central to our approach is the family unit which serves as a reference to identify causal genotype-phenotype correlations. Screening a multitude of 10 overlapping phenotypes revealed disease associated and co-segregating variants in 12 families. These rare or novel protein altering mutations cluster predominantly in genes (NOTCH1, ARHGAP31, MAML1, SMARCA4, JARID2, JAG1) along the Notch signaling cascade. This is in line with a significant enrichment (Wilcoxon, p< 0.05) of variants with a higher pathogenicity in the Notch signaling pathway in patients compared to controls. The significant enrichment of novel protein truncating and missense mutations in NOTCH1 highlights the allelic and phenotypic heterogeneity in our pediatric cohort. We identified novel co-segregating pathogenic mutations in NOTCH1 associated with left and right-sided cardiac malformations in three independent families with a total of 15 affected individuals. In summary, our results suggest that a small but highly pathogenic fraction of family specific mutations along the Notch cascade are a common cause of LVOTO.

Aortic Dilatation Associated With a De Novo Mutation in the SOX18 Gene: Expanding the Clinical Spectrum of Hypotrichosis-Lymphedema-Telangiectasia Syndrome

BACKGROUND We report a 13-year-old female patient followed since birth for multiple rare congenital defects, including hypotrichosis, telangiectasia, and severe dilatation of the ascending aorta. METHODS Comprehensive phenotype assessment throughout childhood included repeated echocardiographic measurements, evaluation of renal function, and immunohistochemical analysis of skin biopsy samples. Whole-exome sequencing was performed for the patient and both unaffected parents. RESULTS We identified a novel de novo mutation in the transcription factor SOX18 (c.481C>T:p.Gln161*) in the patient, which was absent in all unaffected family members. Echocardiography revealed early onset and progressive dilatation of the ascending aorta. Skin biopsy results confirmed the defects of the blood vasculature in the presence of intact lymphatic vessels. Assessment of renal function did not show any signs of renal problems or renal failure in the patient. CONCLUSIONS The genetic finding of a pathogenic SOX18 mutation enabled the diagnosis of the rare hypotrichosis-lymphedema-telangiectasia syndrome in our patient. The identification of a novel stop gain mutation in the SOX18 gene in association with dilatation of the aorta highlights the importance of this gene during the development of the circulatory system. Our study highlights the importance of whole-exome sequencing in the rapid identification of genes and gene mutations involved in rare conditions and thus expanding the knowledge and spectrum of clinical manifestations associated with them.

Influence of Demographic Characteristics of Participants on Consent to Genomic Research into Congenital Heart Disease

Background: The enrollment of sick children and their families in genomics studies calls for a comprehensive view of the consent process. Few studies have searched for correlations between the demographic characteristics of participants (age, gender, parental lineage) or their level of participation (affected children, parents, or other relatives), on the one hand, and patterns of consent to specific pediatric research procedures, on the other (DNA banking, use of cardiac tissue, disclosure of a cardiac condition, creation of cell lines, recall of a participant).

Design and rationale of a genetic cohort study on congenital cardiac disease: experiences from a multi-institutional platform in Quebec.

BACKGROUND Congenital cardiac disease is the most common malformation, and a substantial source of mortality and morbidity in children and young adults. A role for genetic factors is recognised for these malformations, but overall few predisposing loci have been identified. Here we report the rationale, design, and first results of a multi-institutional congenital cardiac disease cohort, assembled mainly from the French-Canadian population of the province of Quebec and centred on families with multiple affected members afflicted by cardiac malformations. METHODS Families were recruited into the study, phenotyped and sampled for DNA in cardiology clinics over the first 3 years of enrolment. We performed segregation analysis and linkage simulations in the subgroup of families with left ventricular outflow tract obstruction (LVOTO). RESULTS A total of 1603 participants from 300 families were recruited, with 169 out of 300 (56.3%) families having more than one affected member. For the LVOTO group, we estimate heritability to be 0.46-0.52 in our cohort. Simulation analysis demonstrated sufficient power to carry out linkage analyses, with an expected mean log-of-odds (LOD) score of 3.8 in 67 pedigrees with LVOTO. CONCLUSION We show feasibility and usefulness of a population-based biobank for genetic investigations into the causes of congenital cardiac disease. Heritability of LVOTO is high and could be accounted for by multiple loci. This platform is ideally suited for multiple analysis approaches, including linkage analysis and novel gene sequencing approaches, and will allow to establish segregation of risk alleles at family and population levels.