Researchers say retroviruses that are dormant in our genome can be triggered by environmental factors and cause diseases such as multiple sclerosis.

Scientists believe we have dead retroviruses in our DNA left behind from our prehistoric ancestors. Getty Images
The human genome is a veritable graveyard of dead retroviruses, making up somewhere between 5 percent and 8 percent of our DNA, according to most credible estimates.

These retroviruses make up much of the junk DNA in our bodies — in essence, leftovers from millions of years of evolution that have been deactivated and set aside.

Sort of like the trash folder on your computer before you empty it.

Spooky, perhaps, but previously thought to be harmless. Except many scientists now aren’t so sure.

Recent research suggests that these human endogenous retroviruses, or HERVs, could, under the right conditions, rise zombie-like to wreak havoc on our bodies.

They may even be at the root of conditions such as multiple sclerosis (MS), amyotrophic lateral sclerosis (ALS), and even schizophrenia.

Retro-what now?
First, let’s talk a little about what a retrovirus is.

In the simplest terms, a retrovirus works by inserting its genome into the DNA of a host cell, thus replacing some of the cell’s “code” with its own.

In humans, the most well-known retrovirus is probably the human immunodeficiency virus (HIV). This is why the common therapy for HIV is antiretroviral drugs.

Most retroviruses are exogenous, which means they attack a person from outside the body and are transmitted through fluid, air, or other contact.

HERVs, by contrast, are endogenous, meaning they’re already within us, coded into our DNA.

These are remainders from when our primordial ancestors were infected with retroviruses. Some of this code got left behind, while their harmful effects were mutated away.

“During evolution, retroviruses were vectors of genetic diversity, jumping from species to species,” Hervé Perron, PhD, one of the pioneers of HERV research and the founder of GeNeuro, a pharmaceutical company developing HERV-specific treatments, told Healthline. “These retroviruses can recombine with the host gene first, so they can embark genes and infect cells while retro-transcribing their genetic information.”

That’s opposed to retroviral cells like in HIV, where only infected cells have inserted copies in their DNA so they are not transmitted hereditarily.

HERVs, by contrast, stick around because these retroviral infections occurred in a significant number of instances in regions that wouldn’t affect the life of the newborn. And so they persisted in our genome.

In some cases, researchers speculate these dead viruses might even have some beneficial effectsTrusted Source, including helping form a prototype immune system as viruses fought other viruses for supremacy

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