According to the data of the World Health Organization, about 18 million people die of cardiovascular disease every year. By 2030, this figure is expected to rise to 23 million, so cardiovascular disease is undoubtedly the number one killer of mankind. However, other mammals like humans – whether chimpanzees, our “close relatives” on land, or marine mammals whales and dolphins – have little such trouble.
Why has human being, as a higher animal, become the only mammal that may suffer from cardiovascular disease? The BBC introduced the latest research findings of American scientists and solved the mystery.
Humans “lost” a single gene
According to a BBC article, the latest research by researchers at the University of California San Diego School of Medicine found that when humans evolved about 2 million to 3 million years ago, they inadvertently “lost” a single gene. This may be the key reason why humans become the only mammal suffering from heart disease. The study, published in the proceedings of the National Academy of Sciences, explained that a gene mutation millions of years ago “inactivated” a gene called CMAH in the human body, and this feature has been passed down from generation to generation, making humans more prone to cardiovascular disease than other animals.
As for the frightening heart disease, the main cause is atherosclerosis. This is a disease in which atherosclerotic plaque deposits on the blood vessel wall and causes arterial stenosis. Atherosclerosis is also the main cause of coronary heart disease, cerebral infarction and peripheral vascular disease. Generally speaking, people will have arteriosclerosis related symptoms after entering middle age.
According to previous studies, atherosclerosis seems to only affect humans, which does not seem to occur in other animals. Ten years ago, American researchers conducted an experiment to observe whether domesticated chimpanzees and other mammals also suffer from heart disease.
Among them, “human close relatives” chimpanzees also have some high-risk living habits like humans, such as sitting still for a long time, high cholesterol diet and high blood pressure. But the results showed that chimpanzees were almost unaffected. Heart disease is extremely rare in chimpanzees. Even if there is, the cause is different from that of humans. Chimpanzee heart disease is caused by a kind of myocardial scar that cannot be explained at present.
Ajit Varki, a researcher who participated in the chimpanzee experiment 10 years ago, also participated in the new experiment. He and his team genetically modified mice to “turn off” the CMAH gene in mice, and then compared it with normal mice.
The experiment found that even if the two groups of mice ate the same food and received the same treatment, the fatty deposits in the blood vessels of mice with “deleted” CMAH gene were at least twice that of normal mice, and the probability of atherosclerosis increased significantly. Therefore, experiments show that the CMAH gene lost in the process of human evolution is likely to be the cause of human susceptibility to cardiovascular disease.
What is the use of CMAH gene?
Of course, in addition to genes, some high-risk factors are also one of the causes of heart disease. In addition to the lack of exercise, high cholesterol, diabetes, obesity, smoking and age, there is a correlation between eating too much red meat and heart disease. The CMAH gene lost in human evolution can produce a sialic acid called Neu5Gc, which will be useful when we eat red meat. Without CMAH gene, humans lack Neu5Gc sialic acid, and red meat is rich in Neu5Gc.
Therefore, we are repeatedly exposed to Neu5Gc when eating red meat. The researchers say this triggers an immune response and a chronic inflammation called “xenomyocarditis”, which increases the risk of heart disease and cancer. The genetically modified mice had a 2.4-fold increase in atherosclerosis after eating a food rich in Neu5Gc.
Interestingly, about 15% of patients with first heart attack do not have any of the above high risk factors at all. In other words, their lifestyle is very healthy. This may explain that genes may be the reason why some healthy vegetarians also suffer from heart disease.
How did humans “lose” the CMAH gene? Researchers said that exactly when and why humans lost the CMAH gene is still a mystery.
Scientists have made it clear that the “loss” of the CMAH gene gave the human ancestor Homo sapiens the ability to run long distances, but also reduced their fertility. These may be the result of natural selection for the survival of the fittest. The bad news is that this may increase the risk of heart disease, making modern humans the only mammal suffering from cardiovascular disease. However, this new scientific discovery may open a new door to the treatment of cardiovascular diseases in the future.