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Why Only Humans Have Heart Attacks?

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A heart attack, also called a myocardial infarction, is caused by atherosclerosis, a condition in which abnormal deposits of fatty material build up in the walls of coronary arteries, leading to reduced blood flow or complete blockage. Every year, about 790,000 Americans have a heart attack, according to the CDC.

Ever wondered why only humans have heart attacks and they are so rare in other animals, even in chimpanzees, our very close genetic cousins?

Researchers at the University of California San Diego School of Medicine have an interesting explanation.

The loss of a gene known as CMAH, millions of years ago, in our ancestors has made humans prone to cardiovascular disease. CMAH produces Neu5Gc, a sialic acid sugar molecule.

But what caused the loss of CMAH in our ancestors?

Two to three million years ago, our ancestors - Hominins- in the course of evolution, had a mutation in the gene CMAH. By that mutation, they became resistant to Plasmodium reichenowi, the malaria-causing parasite in chimpanzees, according to the researchers.

The Study…

As part of the study, mice were modified to be deficient of CMAH and Neu5Gc, and the severity of atherosclerosis in the modified mice was compared to control mice, which retained the CMAH gene that produces Neu5Gc.

There was an almost 2-fold increase in the severity of atherosclerosis in mice when the CMAH gene and Neu5Gc were eliminated compared to unmodified mice.

Commenting on the findings, one of the authors of the study, Ajit Varki, Distinguished Professor Of Medicine and Cellular And Molecular Medicine at the University of California, San Diego, said, "The increased risk appears to be driven by multiple factors, including hyperactive white cells and a tendency to diabetes in the human-like mice. This may help explain why even vegetarian humans without any other obvious cardiovascular risk factors are still very prone to heart attacks and strokes, while other evolutionary relatives are not."

When the mice modified to lack the CMAH gene were fed a Neu5Gc-rich, high-fat diet, they subsequently suffered a further 2.4-fold increase in atherosclerosis. Red meats are particularly rich in Neu5Gc.

Repeated exposure to Neu5Gc by consuming red meats triggers an immune response and chronic inflammation, a condition termed as "xenosialitis" that promotes atherosclerosis, explain the researchers.

The findings are published in PNAS, a peer-reviewed journal.

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