Jul 2, 2019
Jane Ferguson: Hi, everyone. Welcome to episode 29 of Getting Personal: Omics of the Heart, the podcast from Circulation: Genomic and Precision Medicine. I'm Jane Ferguson from Vanderbilt University Medical Center and an associate editor at Circ: Genomic and Precision Medicine. Let's dive in and see what's new in the June issue.
First up, Validation of Genome-Wide Polygenic Risk Scores for Coronary Artery Disease in French Canadians from Florian Wünnemann, Guillaume Lettre and colleagues from the University of Montreal. Polygenic scores have the potential to be used to predict disease risk, but have not been broadly validated in different populations. This team was interested in whether polygenic risk scores that have been found to predict coronary artery disease in European ancestry subjects in the UK Biobank would also predict disease in French Canadians. They calculated two different polygenic risk scores in over 3600 cases and over 7000 controls and tested their ability to predict prevalent, incident and recurrent CAD.
Both scores predicted prevalent CAD, but did not perform as well in predicting incident or recurrent disease. This maybe because the majority of subjects were on statant treatment. Overall, the study confirms that polygenic risk scores for CAD developed in European ancestry can be used in other populations of European ancestry. However, further work is needed to develop and validate polygenic risk scores in other ancestries and to explore whether well performing risk scores can be developed to predict incident or recurrent disease.
Our next paper comes from Farnaz Shoja-Taheri, Michael Davis and colleagues from Emory University and is entitled Using Statistical Modeling to Understand and Predict Pediatric Stem Cell Function. Stem cell therapy is emerging as a potential therapeutic option for treating pediatric heart failure, which otherwise can only be cured through heart transplantation. The success of stem cell therapy depends on many variables, including the reparative ability of the infused cells. In this paper, the author set out to test whether they could predict the behavior of c-kit+ progenitor cells or human CPCs using RNA seq and computational modeling.
They obtained CPCs from 32 patients, including eight neonates whose cells are thought to have the highest reparative capacity, and they performed RNA sequencing. The team had previously developed regression models that could link gene expression data from sequencing to phenotypes in the cells, and they tested these models in the CPC cell lines. They tested seven neonate cell lines in vitro and found that cellular proliferation and the chemotactic potential of condition media matched what was predicted by the RNA seq-based model.
They used pathway analysis to identify potential mechanisms regulating CPC performance and identified several genes related to immune response, including interleukins and chemokines. They further confirmed the presence of cytokines at the protein level that were associated with well performing cells showing that at least one of the outcomes could be functionally predicted using an ELISA ASA. This type of approach may prove useful to inform ongoing clinical trials to stem cell therapy in congenital heart disease.
The next paper, Systems Pharmacology Identifies an Arterial Wall Regulatory Gene Network Mediating Coronary Artery Disease Side Effects of Antiretroviral Therapy comes to us from Itziar Frades, Johan Björkegren, Inga Peter and colleagues from the Icahn School of Medicine at Mount Sinai. They were interested in understanding mechanisms whereby antiretroviral therapy for HIV leads to increased risk for coronary artery disease. They analyzed the transcriptional responses to 15 different antiretroviral therapy or ART drugs in human cell lines and cataloged the common transcriptional signatures.
They then cross-referenced these against gene networks associated with CAD and CAD related phenotypes. They found that 10 of 15 ART response networks were enriched for differential expression and connectivity in an atherosclerotic arterial wall of regulatory gene network identified as causal for CAD. They used cholesteryl ester loaded foam cells in an in vitro model to validate their findings and found that ART treatment increased cholesteryl ester accumulation in foam cells which was prevented when the key network regulator gene, PQBP1, was silenced.
Their study highlights a gene network which is altered in response to ART and which promotes foam cells formation, highlighting a mechanistic link between HIV treatment and CAD. Targeting this network potentially through PQBP1 maybe a way to reduce the risk of CAD in individuals treated with antiretroviral drugs. The next paper comes from Brooke Wolford, Whitney Hornsby, Cristen Willer, Bo Yang and colleagues from the University of Michigan and is entitled Clinical Implications of Identifying Pathogenic Variants in Individuals With Thoracic Aortic Dissection. They were interested in whether exome sequencing in individuals with thoracic aortic dissection could identify disease associated variance.
They conducted exome sequencing in 240 patients and 258 controls and screened 11 genes for potentially pathogenic variance. They identified 24 variance in six genes across 26 cases with no potentially pathogenic variance identified in the controls. They found that carriers of pathogenic variance had significantly earlier age of onset of dissection, higher rates of root aneurysm and greater incidents of aortic disease in family members, while patients without identified variance had more hypertension and a higher rate of smoking.
Their study suggests that genetic testing should be considered in patients with thoracic artery dissection particularly in individuals with early age of onset before age 50 and no hypertension with the possibility of cascade screening to follow to identify at risk family members before onset of dissection and possible death. Our next paper is a research letter from Seyedeh Zekavat, Pradeep Natarajan and colleagues from Harvard Medical School, Investigating the Genetic Link Between Arterial Stiffness and Atrial Fibrillation. They aimed to investigate whether arterial stiffness is causal for atrial fibrillation using Mendelian randomization to probe genetic causality.
They calculated the genetic component of the arterial stiffness index or ASI, a noninvasive measure of arterial stiffness, in over 131,000 individuals in the UK Biobank. They then assessed whether the genetic predictors of ASI defined as the top six independent variance were also associated with atrial fibrillation in over 225,000 participants in the UK Biobank and in over 588,000 individuals from a multi-ethnic GWAS. They found that the ASI genetic risk score was significantly associated with incident atrial fibrillation in both the UK Biobank and the multi-ethnic AF GWAS.
The association held true even after adjustment for age, sex, smoking status, prevalent heart failure, prevalent hypertension, prevalent CAD, prevalent hypercholesterolemia, prevalent diabetes, heart rate, alcohol intake and exercise frequency in the UK Biobank participants. Because some people have hypothesized that atrial fibrillation may actually precede and cause arterial stiffness, the team did the reverse Mendelian randomization experiment and tested whether genetic predictors of AF were associated with the arterial stiffness index. They found no association suggesting that AF does not cause arterial stiffness.
In summary, this paper provides genetic evidence supporting arterial stiffness as a causal contributor to atrial fibrillation and suggests that future randomized controlled studies would be warrantied to assess whether methods to reduce arterial stiffness could be protective against atrial fibrillation. The next research letter comes from Scott Damrauer, Kara Hardie, Reed Pyeritz and colleagues from the University of Pennsylvania and is entitled FBN1 Coding Variants and Nonsyndromic Aortic Disease. In this study, the authors were interested in characterizing the frequency of variance associated with Marfan syndrome in the general population.
They analyzed data from the Penn Medicine BioBank looking at 12 variance in the FBN1 gene all of which have been reported to associate with Marfan syndrome. Of almost 11,000 individuals who underwent exome sequencing, they identified 70 individuals who were carriers of one of the 12 preselected FBN1 variance. These individuals ranged in age from age 28 to 87 years and 56% of them were male. They combed through clinical data from the participant's electronic health records, including office notes, diagnostic tests and imaging studies.
Two individuals had a clinical diagnosis of Marfan syndrome while 21 individuals had evidence of cardiovascular phenotypes related to Marfan syndrome including mitral valve disease, dilated sinus of valsalva, dilated ascending aorta, descending thoracic or abdominal aneurysms or dissections or had undergone surgical procedures involving the mitral valve or thoracic aorta. Compared to age and sex matched controls without known or suspected pathogenic FBN1 variance, the FBN1 variant carriers were significantly more likely to have Marfan syndrome related cardiovascular disease.
Although the majority of individuals carrying FBN1 variance did not have documented cardiovascular disease in this study, the data were somewhat limited, meaning that some affected individuals could have been missed. Thus, while the penetrance of these variance appears to be variable, the severe consequences of these FBN1 variance observed in some individuals suggests that clinical screening for carries of these variance is important. To round up this month's issue, we have a scientific statement led by Ferhaan Ahmad and Elizabeth McNally on Establishment of Specialized Clinical Cardiovascular Genetics Programs: Recognizing the Need and Meeting Standards.
This statement comes from the American Heart Association Council on Genomic and Precision Medicine, the Council on Arteriosclerosis, Thrombosis and Vascular Biology, the Council on Basic Cardiovascular Sciences, the Council on Cardiovascular and Stroke Nursing, the Council on Clinical Cardiology and the Stroke Council. In this statement, the writing group lays out the importance of establishing specialized centers of care for individuals affected by inherited cardiovascular diseases. As cardiovascular genetics as a field continues to grow and as genomic medicine becomes part of practice, it is essential for programs to evolve to include this new knowledge and specialization.
There are significant challenges in interpreting genetic test results and in evaluating counseling and managing the care of genetically at risk family members who have inherited pathogenic variance, but not yet shown signs of disease. Establishing specialized programs to combine cardiovascular medicine and genetics expertise is an effective way to allow for the integration of multiple types of clinical and genetic data and to improve diagnosis, prognostication and cascade family testing in affected individuals and their families.
Training individuals in genetic cardiology will allow for improved care and management of risk in affected or at risk individuals and potentially pave the way for genotype specific therapy. This important and timely scientific statement outlines current best practices for delivering cardiovascular genetic evaluation and care in both the pediatric and the adult settings with a focus on team member expertise and conditions that most benefit from genetic evaluation.
That's all for this month. Thank you as always for listening and come back next month for the next installment of papers in Genomic and Precision Medicine. This podcast was brought to you by Circulation: Genomic and Precision Medicine and the American Heart Association Council on Genomic and Precision Medicine. This program is copyright American Heart Association 2019.