Bicuspid aortic valve (BAV) is a common congenital heart defect where the aortic valve has two leaflets (cusps) instead of the usual three, resulting in abnormal blood flow and development of aortic valve diseases such as aortic stenosis and incompetence. In addition, the BAV is sometimes accompanied by development of an enlarged aorta – the main artery in the body. Both the bicuspid aortic valve and an enlarged aorta often require cardiac surgery, usually after the age of 50 years. Despite this, only a limited number of genes have been associated with the disease and the molecular mechanisms remain unexplained in most cases.
In a new study aimed to further understand the genetic architecture of BAV, an international group of researchers led by Boston University Chobanian & Avedisian School of Medicine and Laval University in Quebec City, Canada, along with the Bicuspid Aortic Valve Consortium, the Genetic Aortic Network (a division of The Marfan Foundation) and participating Institutions, believe the condition is strongly influenced by the cumulative effect of variation in many different genes(polygenic contribution).
“We found that variation in 36 genetic regions increases the risk of a bicuspid aortic valve. These findings support the notion that bicuspid aortic valve disease is an inherited disease caused by a combination of many common genetic variants, not merely a single mutation in a single gene,” explains co-corresponding author Simon C. Body, MD, MPH, professor of anesthesiology at Boston University Chobanian & Avedisian School of Medicine.
From a group of 65 677 US, Canadian and European participants, the researchers performed a genome-wide association study (GWAS) meta-analysis on 9631 individuals with BAV. After identifying general genetic regions through GWAS, they used RNA sequencing to study gene activity (expression levels) in specific, relevant tissues.
They observed 36 regions with genetic variants associated with a bicuspid aortic valve, four of which had been previously identified. They prioritised 55 genes in these regions based upon expression in human aortic valve tissues from individuals who had surgery, then tested the effect of changing four selected genes, upon heart development in an experimental model, demonstrating that all four altered genes had effects on development of the valve. The researchers also looked at the effect of these genes in a statistical model finding a three-fold increase in risk for a BAV in individuals in the top 10% and association with aortic aneurysmal disease, a bulge in the aortic wall that can rupture. Some of these 36 genetic regions are also involved in aortic stenosis and aortic aneurysm development, which could lead to better prediction of these complications in people with BAV and point to biological mechanisms responsible for these joint effects.
According to the researchers, while these findings support the notion that BAV is an inherited disease, the findings do not currently support genetic testing, either prenatally or later in life, for predicting a bicuspid aortic valve. “Echocardiography and other imaging modalities remain the gold standard for diagnosis. In addition, the identified heritability supports performing screening echocardiography on first-degree relatives of a person with an identified bicuspid valve,” adds Body.
These findings appear online in the journal Circulation.
Source: University of Boston
