What can an ice mummy teach us about heart disease?
Looking at the list of common risk factors, you can easily see how a modern lifestyle can increase a person’s risk of having heart disease. On average, people eat more, smoke more, and walk less than our ancestors. But if heart disease was simply a product of our modern lifestyle, why do so many mummies have it?
This is the question a group of researchers hoped to answer in 2012 when they tested DNA from an ancient ice mummy known as Ötzi. Approximately 5,300 years ago, a stone arrow penetrated Ötzi’s back, clipping a major artery along the way1. It likely wasn’t long before he fell—not just to the cold mountain soil, but to his icy tomb. The cold and relatively dry climate where he died prevented his body from decaying as it normally would. Instead, the ice mummified him, preserving much of his remains in the process2.
After being discovered, scientists around the world took an interest in Ötzi because his uniquely preserved body offered a rare glimpse into the life of a Copper Age human. Written history only began about 4,000 years ago, so we know relatively little about human life before then. But Ötzi’s body was so well preserved that scientists could see the tattoos covering his body, determine what his final meal was, and piece together various aspects of his life and death2. Analysis showed that he was a fit person, likely in his 40s who intensively hiked around the foothills of the Italian alps. Black marks in his lungs indicated that he was probably around open campfires throughout his life. The arrowhead that killed him was still in his shoulder, along with other signs of trauma. But one intriguing observation was that Ötzi seemed to have heart disease2,3.
Heart disease is a broad term describing many conditions that affect our hearts ability to pump blood. A common symptom of heart disease is atherosclerosis—the progressive thickening of artery walls that can lead to decreased blood flow, blood clots, heart attacks, and ischemic stroke4. Ötzi showed signs of having atherosclerosis and a similar condition where blood vessels are blocked by bone-like deposits in the vessel wall (known as calcification)3. There are many reasons atherosclerosis and calcified vessels develop, but most of them are features of modern life4. So why did a fit man, with a diverse diet, develop heart disease?
As far back as the early 1900s, researchers have observed signs of heart disease in multiple Egyptian mummies2,5. In 2013, scientists expanded this research by scanning the bodies of 137 mummies from around the world (from ancient Peruvian, Puebloans, Unangan, and Egyptian cultures) in search of telltale signs of heart disease. They found that over 37% of the mummies showed signs of heart disease5. With a wide range of cultures, ages, diets, and lifestyles represented in this study, researchers concluded that heart disease was likely influenced by something other than environmental factors—possibly DNA.
In modern humans, we know that DNA can affect a person’s likelihood of developing heart disease6. The condition known as familial hypercholesterolemia (FH) is a good example. This condition results when people inherit variants in their DNA which cause their body to process cholesterol differently, ultimately leading to dangerously high blood cholesterol levels. There’s a whole spectrum of heart conditions that can be influenced by DNA, ranging from FH to cardiomyopathies. Large scale studies continue to identify variants in people’s DNA that are associated with various forms of heart disease7.
When researchers sequenced Ötzi’s DNA in 2012, they found many variants with strong links to heart disease3. In total, Ötzi had double the likelihood of developing heart related health conditions due to his DNA2. He’s not the only one, either: similar results have been found in a 400-year-old Korean mummy who also showed signs of calcified blood vessels and was genetically predisposed to heart disease8.
Findings like these are great examples of how genetics can predispose individuals to heart disease, even those who live healthy lifestyles. Decades of research suggest that this is because heart disease can be the product of both a person’s DNA and their environment9. Ongoing research aims to expand our understanding of how a person’s genetics and environment interact to cause these types of conditions.
2Zink, Albert, et al. “Genomic Correlates of Atherosclerosis in Ancient Humans.” Global Heart, vol. 9, no. 2, 2014, pp. 203–209., doi:10.1016/j.gheart.2014.03.2453.
3Keller, Andreas, et al. “New Insights into the Tyrolean Iceman’s Origin and Phenotype as Inferred by Whole-Genome Sequencing.” Nature News, Nature Publishing Group, 28 Feb. 2012, http://www.nature.com/articles/ncomms1701.
4Liu, Wei et al. “Current Understanding of Coronary Artery Calcification.” Journal of Geriatric Cardiology : JGC 12.6 (2015): 668–675. PMC. Web. 9 Oct. 2018.
5Thompson, R.c., et al. “Atherosclerosis Across 4000 Years of Human History: The Horus Study of Four Ancient Populations.” Journal of Vascular Surgery, vol. 58, no. 2, 2013, p. 549., doi:10.1016/j.jvs.2013.06.006.
6“Heart Disease.” Centers for Disease Control and Prevention, Centers for Disease Control and Prevention, 28 Nov. 2017, http://www.cdc.gov/heartdisease/facts.htm.
7Kathiresan, Sekar, and Deepak Srivastava. “Genetics of Human Cardiovascular Disease.” Cell 148.6 (2012): 1242–1257. PMC. Web. 9 Oct. 2018.
8Shin, Dong Hoon et al. “Paleogenetic Study on the 17th Century Korean Mummy with Atherosclerotic Cardiovascular Disease.” Ed. David Caramelli. PLoS ONE 12.8 (2017): e0183098. PMC. Web. 8 Oct. 2018.
9Khera, Amit V. et al. “Genetic Risk, Adherence to a Healthy Lifestyle, and Coronary Disease.” The New England journal of medicine 375.24 (2016): 2349–2358. PMC. Web. 9 Oct. 2018.