Congenital heart disease (CHD) is a complex group of birth defects affecting approximately 1 per cemt of live-born infants, and is a leading cause of neonatal mortality. The genetic basis is known in less than 20 per cent cases. We are using next-generation sequencing to identify the genomic basis of CHD. Our study subjects are part of an Ontario-wide biobank and we have currently enrolled 6225 participants with various pediatric heart diseases.

Recently we identified de-novo variants on a highly conserved gene NR2F2 (nuclear receptor subfamily 2, group F, member 2) in a cohort of Atrioventricular septal defects (AVSD) using whole exome sequencing (Al Turki S, Manickaraj AK, Mercer CL, Gerety SS,  et.al., An J Hum Genet, 2014), and also identified mutations in several syndrome-associated genes in this cohort (D’Alessandro LC, Al Turki S, Manickaraj AK, Manase D, et.al., Genet Med, 2016). Currently, we are studying patients with bicuspid aortic valve-associated aortopathy, hypoplastic left heart syndrome, tetralogy of Fallot and other CHDs.

Cardiomyopathies are diseases of the heart muscle that cause the ventricles to be weak and enlarged, or thick and stiff resulting in heart failure. There are five major types: dilated cardiomyopathy (DCM), hypertrophic cardiomyopathy (HCM), arrhythmogenic cardiomyopathy (AC), left ventricular non-compaction (LVNC), and restrictive cardiomyopathy (RCM). The genetic basis is known in less than 50 per cent cases. We are using next-generation sequencing to identify the genetic causes of cardiomyopathies, to determine how mutation type and number influence outcomes, and to study patient iPSC-derived cardiac lineages to model disease and test drugs.

Improved surgical methods have improved survival in CHD. However, the repaired hearts can fail over time. We previously reported that dysregulation of key adaptive genes like hypoxia response genes, and neurohormonal genes (renin-angiotensin, adrenergic) contributes to failure of the ventricles to adapt to stress in patients with tetralogy of Fallot, cardiomyopathy, and after transplant (Jeewa A, Manickaraj AK, Mertens L, Manlhiot C, et. al., Pediatr Res, 2012), (Mital S, Chung WK, Colan SD, Sleeper LA et. al., Circulation 2011), (Alkon J, Friedberg MK, Manlhiot C, Manickaraj AK, Pediatr Res, 2012). We also showed that these genetic variations can influence response to surgery (Mital S, Chung W, Colan SD, Sleeper LA et al., Circulation, 2011).

Through the Ted Rogers Centre for Heart Research, we are now employing a systems biology approach to decipher the molecular signature of myocardial and vascular adaptation in CHD and cardiomyopathies using whole exome or whole genome sequencing. The goal is to identify genomic markers of heart failure, gene and protein expression profiling of myocardium and patient iPSC-derived lineages to eventually find new drug targets within the dysregulated molecular pathways.

How we respond to drugs depends on our genes. We showed that immunosuppressive medicines are cleared differently by different patients after transplant depending on their genetic make-up (Gijsen V, Mital S, van Schail R, Soldin S, et al., J Heart Lung Transplant, 2011). We also showed how knowing a patient’s genotype may help us identify those likely to respond to beta blockers in children with dilated cardiomyopathy so that we can avoid futile use of beta-blockers in the remaining patients (Reddy S, Fung A, Manlhiot C, Tierney ES et.al., Pediatr Res, 2015).

We have established a national pediatric transplant network to employ age-appropriate and genotype-guided strategies to personalized immunosuppression in children after solid organ transplants, and are expanding use of pharmacogenetic approaches in heart failure through our Cardiac Precision Medicine program.

How we respond to drugs depends on our genes. We showed that immunosuppressive medicines are cleared differently by different patients after transplant depending on their genetic make-up (Min S, et al., Pediatr Transplant, 2018), (Gijsen V, Mital S, van Schail R, Soldin S, et al., J Heart Lung Transplant, 2011). We also showed how knowing a patient’s genotype may help us identify those likely to respond to beta blockers in children with dilated cardiomyopathy so that we can avoid futile use of beta-blockers in the remaining patients (Reddy S, Fung A, Manlhiot C, Tierney ES et.al., Pediatr Res, 2015).

We have established a national pediatric transplant network to employ age-appropriate and genotype-guided strategies to personalized immunosuppression in children after solid organ transplants (Papaz T, et al. Transplant Direct, 2018), and are expanding use of pharmacogenetic approaches in heart failure through our Cardiac Precision Medicine program.

Childhood cancer survivors are at risk for late complications often related to cancer therapy. Cardiac disease is the third leading cause of premature death in childhood cancer survivors (after cancer recurrence and second malignancies), with a 7-fold increased risk of premature cardiac death as compared to the general population. Through a collaborative team of oncologists and cardiologists, we are studying novel approaches to the prediction, diagnosis and treatment of cardiac late effects in survivors of childhood cancer, with special emphasis on identifying genomic predictors and early biomarkers of cardiac toxicity that can be used to employ cardioprotective strategies in at-risk children. A large cohort of ~1100 paediatric cancer acute and long-term survivors have been recruited for genomics and study of biomarkers.

The Nobel prize-winning technology that allows reprogramming of somatic cells into an embryonic state has revolutionized the approach to the study of human disease. We have established one of the largest banks of skin fibroblasts from children with heart disease and are using cardiac lineages derived from patient iPSCs to model heart disease in a dish and test new drugs. It is hoped that this approach will expedite the search for new therapies.

Cardiomyopathies are the leading cause of heart failure and sudden cardiac death in children. With the help of stem cell experts, we reprogram samples from patients with cardiomyopathies into iPSCs, differentiate them into cardiomyocytes, and study their phenotype in vitro.

1. Patients with elastin insufficiencyas seen in Williams Beuren syndrome (WBS) are born with cardiovascular defects caused by narrowing of blood vessels due to proliferation of the smooth muscle cells lining the blood vessels. Surgery can relieve the obstruction but it often recurs and there are no drugs to treat this condition. We modelled WBS using patient derived iPS-smooth muscle cells and showed partial rescue of the cellular abnormalities seen in this disease (Kinnear C, Chang WY, Khattak S et al., Stem Cells Transl Med. 2013). Cells from additional WBS patients and patients carrying elastin mutations are currently being investigated.
2. Hypoplastic left heart syndromeis a severe cardiac malformation characterized by a poorly developed left ventricle. We found that these hypoplastic left ventricles have an aging phenotype early on in fetal life and that this phenotype can be reproduced in a dish using stem cell derived cardiomyocytes, smooth muscle and endothelial cells (Gaber N, Gagliardi M, Patel P et al., Am J Pathol. 2013). This cellular model allowed us to study signaling defects in fetal stage cells and may have implications in the study of environmental and teratogenic factors on cardiac development.

The vision of Ted Rogers Centre for Heart Research (TRCHR) is to transform and dramatically improve the future of heart health for children, adults and families across Canada and around the world. In the next 10 years the centre aims to reduce hospitalization by 50 per cent and implement devices in patient homes to enable remote monitoring for cardiac function.

Our research team focuses on studying the genetics of heart diseases and we are constantly working on studies that aim to decode genetic foundation for cardiac diseases and to discover methods for implementing patient specific drugs to treat heart diseases. Currently our research team is also conducting myocardial tissue studies to decode the genetic foundations of cardiac disease on genomic, transcriptional, and translational levels. In these tissues proteomic studies are being done in parallel with RNA-sequencing to unravel biomarkers that play important roles in causing heart diseases and use that knowledge to aid us in searching for therapeutic targets.