Rare variants in KDR, encoding VEGF Receptor 2, are associated with tetralogy of Fallot.

PURPOSE: Rare genetic variants in KDR, encoding the vascular endothelial growth factor receptor 2 (VEGFR2), have been reported in patients with tetralogy of Fallot (TOF). However, their role in disease causality and pathogenesis remains unclear. METHODS: We conducted exome sequencing in a familial case of TOF and large-scale genetic studies, including burden testing, in >1,500 patients with TOF. We studied gene-targeted mice and conducted cell-based assays to explore the role of KDR genetic variation in the etiology of TOF. RESULTS: Exome sequencing in a family with two siblings affected by TOF revealed biallelic missense variants in KDR. Studies in knock-in mice and in HEK 293T cells identified embryonic lethality for one variant when occurring in the homozygous state, and a significantly reduced VEGFR2 phosphorylation for both variants. Rare variant burden analysis conducted in a set of 1,569 patients of European descent with TOF identified a 46-fold enrichment of protein-truncating variants (PTVs) in TOF cases compared to controls (P = 7 × 10-11). CONCLUSION: Rare KDR variants, in particular PTVs, strongly associate with TOF, likely in the setting of different inheritance patterns. Supported by genetic and in vivo and in vitro functional analysis, we propose loss-of-function of VEGFR2 as one of the mechanisms involved in the pathogenesis of TOF.

Germline variants in HEY2 functional domains lead to congenital heart defects and thoracic aortic aneurysms.

PURPOSE: In this study we aimed to establish the genetic cause of a myriad of cardiovascular defects prevalent in individuals from a genetically isolated population, who were found to share a common ancestor in 1728. METHODS: Trio genome sequencing was carried out in an index patient with critical congenital heart disease (CHD); family members had either exome or Sanger sequencing. To confirm enrichment, we performed a gene-based association test and meta-analysis in two independent validation cohorts: one with 2685 CHD cases versus 4370 . These controls were also ancestry-matched (same as FTAA controls), and the other with 326 cases with familial thoracic aortic aneurysms (FTAA) and dissections versus 570 ancestry-matched controls. Functional consequences of identified variants were evaluated using expression studies. RESULTS: We identified a loss-of-function variant in the Notch target transcription factor-encoding gene HEY2. The homozygous state (n = 3) causes life-threatening congenital heart defects, while 80% of heterozygous carriers (n = 20) had cardiovascular defects, mainly CHD and FTAA of the ascending aorta. We confirm enrichment of rare risk variants in HEY2 functional domains after meta-analysis (MetaSKAT p = 0.018). Furthermore, we show that several identified variants lead to dysregulation of repression by HEY2. CONCLUSION: A homozygous germline loss-of-function variant in HEY2 leads to critical CHD. The majority of heterozygotes show a myriad of cardiovascular defects.

Apical hypertrophic cardiomyopathy with subendocardial late gadolinium enhancement in an adolescent.

A 17-year-old boy with a history of dyspnea attacks and chest pain was referred to our paediatric cardiology department. Electrocardiogram at presentation showed T-wave inversion in the inferior leads. Cardiovascular magnetic resonance imaging revealed the rare diagnosis of apical hypertrophic cardiomyopathy with subendocardial late gadolinium enhancement, missed by echocardiography.

Functional zebrafish studies based on human genotyping point to netrin-1 as a link between aberrant cardiovascular development and thyroid dysgenesis.

Congenital hypothyroidism caused by thyroid dysgenesis (CHTD) is a common congenital disorder with a birth prevalence of 1 case in 4000 live births, and up to 8% of individuals with CHTD have co-occurring congenital heart disease. Initially we found nine patients with cardiac and thyroid congenital disorders in our cohort of 158 CHTD patients. To enrich for a rare phenotype likely to be genetically simpler, we selected three patients with a ventricular septal defect for molecular studies. Then, to assess whether rare de novo copy number variants and coding mutations in candidate genes are a source of genetic susceptibility, we used a genome-wide single-nucleotide polymorphism array and Sanger sequencing to analyze blood DNA samples from selected patients with co-occurring CHTD a congenital heart disease. We found rare variants in all three patients, and we selected Netrin-1 as the biologically most plausible contributory factor for functional studies. In zebrafish, ntn1a and ntn1b were not expressed in thyroid tissue, but ntn1a was expressed in pharyngeal arch mesenchyme, and ntn1a-deficient embryos displayed defective aortic arch artery formation and abnormal thyroid morphogenesis. The functional activity of the thyroid in ntn1a-deficient larvae was, however, preserved. Phenotypic analysis of affected zebrafish indicates that abnormal thyroid morphogenesis resulted from a lack of proper guidance exerted by the dysplastic vasculature of ntn1a-deficient embryos. Hence, careful phenotyping of patients combined with molecular and functional studies in zebrafish identify Netrin-1 as a potential shared genetic factor for cardiac and thyroid congenital defects.