The genes that lead to coronary artery disease (CAD) also influence reproduction, research shows.
In order to reproduce successfully, researchers say, the genes for heart disease will also be inherited.
“…we suspected there must have been be some unknown benefit to retaining these genes for the disease.”
“Evolution, it seems, is involved in a trade-off where CAD only begins to appear at around 40-50 years of age when the potential beneficial effects of these genes on reproduction have already occurred,” explains lead author Sean Byars from the School of BioSciences at the University of Melbourne.
He says the team wanted to understand more about how CAD has been inherited in our evolutionary past, to better understand why it is so prevalent now.
An ancient disease
“CAD is often thought of as modern disease, but actually atherosclerosis, or thickening of the artery walls, has been detected in Egyptian mummies, so we suspect it has been in our genes for thousands of years.”
CAD currently affects 110 million people and causes 8.9 million deaths annually, according to 2015 figures.
“According to the theory of natural selection, as proposed by Charles Darwin, genes for traits that improve individual survival or reproduction will increase or be maintained in populations, whereas those that reduce our chances of survival will be selected against and gradually removed or reduced over time.
“So it was unclear why CAD remains so common in modern humans and this is important to understand given the global health burden it represents,” explains Byars.
The team analyzed 56 genetic regions for CAD in 12 worldwide populations originating mainly from Africa, Europe, and East Asia, and used a statistical score to measure whether there had been recent selective changes to DNA associated with the disease.
‘Some unknown benefit’
Associate Professor Michael Inouye, who also led the study, says the findings show that many genes associated with CAD have actually been positively selected through evolution.
“So we suspected there must have been be some unknown benefit to retaining these genes for the disease,” says Inouye, based at the Baker Heart and Diabetes Institute.
“After further research, we found CAD genes are also important for reproduction and involved in important functions in male and female fertility being expressed in the testes, ovaries, and endometrium, for example.
“This represents direct evidence that genes that have been under selection are also beneficial for reproduction and, yet, are associated with occurrence of a common disease later in life,” Inouye says.
“This doesn’t necessarily mean that women with many children are more likely to develop heart disease, it may simply mean that the disease is a by-product of humans being able to reproduce well,” adds Byars.
The results also provide insights on how selection for CAD genes differs between populations, and how these populations might respond differently to the same heart disease prevention strategies.
Reading before writing
Inouye says that ultimately these results give us some idea how complicated the effects of genes can be.
He adds that we need to be cautious with new gene-editing techniques like CRISPR, as unintended effects may be introduced which may not reveal themselves for decades or more.
“It’s a bit like a balloon, if you push on one side of it, the air will push out in other places and if you don’t know what the balloon looks like then you won’t be able to predict where.
“Our genomes are similarly complex and we need to learn more in order to read them, much less write them.”
The study appears in the journal PLOS Genetics.
Source: University of Melbourne