Background – did you know?

Approximately 8% of human DNA comprises genetic sequences inherited from ancient viruses. These sequences, known as human endogenous retroviruses (HERVs), date back hundreds of thousands to millions of years, with some predating the emergence of Homo sapiens.

A recent study indicates that specific ancient viral DNA sequences in the human genome influence susceptibility to psychiatric disorders such as schizophrenia, bipolar disorder, and major depressive disorder.

HERVs are remnants of infections by ancient retroviruses, which are viruses that incorporate a copy of their genetic material into the DNA of the host cells they infect.

Retroviruses likely infected humans multiple times throughout evolutionary history. When these infections occurred in sperm or egg cells, the retroviral genetic material was passed to subsequent generations, becoming a permanent part of our genetic lineage.

What is this alien DNA up to?

Initially, scientists considered HERVs to be “junk DNA,” portions of our genome with no apparent function. However, as our understanding of the human genome has advanced, it has become clear that this so-called junk DNA serves more functions than originally thought.

Researchers first discovered that HERVs can regulate the expression of other human genes. A genetic feature is considered “expressed” when its DNA segment is used to produce RNA (ribonucleic acid) molecules.

These RNA molecules can act as intermediaries leading to the production of specific proteins or help regulate other parts of the genome.

Initial research suggested that HERVs regulate the expression of neighbouring genes with crucial biological functions. One example is a HERV that regulates a gene that modifies connections between brain cells.

HERVs have also been found to produce RNAs and even proteins in blood and brain samples. These molecules can perform various functions as they move across cellular compartments.

Scientists have also found evidence that specific human genes are derived from HERVs, indicating that HERVs were co-opted for specialized biological functions during evolution.

For example, the human genes syncytins 1 and 2, derived from HERVs, play essential roles in placental development.

Given the abundance of HERVs in the genome and their potentially numerous functions, we aimed to understand whether genetic susceptibility to certain psychiatric disorders was associated with differences in HERV expression.

Virus DNA is linked with Depression and Schizophrenia.

Duarte and colleagues have profiled HERV expression in nearly 800 autopsy brain samples, identifying DNA variations that influenced HERV expression in the brain. They then cross-referenced this data with findings from large genetic studies comparing genetic differences between tens of thousands of individuals with and without mental health conditions. These studies identified DNA variations associated with different psychiatric conditions.

In turn, they found that the expression of four HERVs was linked to genetic susceptibility to major psychiatric disorders. The expression of two of these HERVs was associated with schizophrenia, one with both schizophrenia and bipolar disorder, and one with depression.

These results suggest that HERVs may play a more significant role in the brain than previously thought.

Many genes are involved in psychiatric disorders, and HERVs are only part of this complex puzzle. Although further research is needed to understand the precise impact of these HERVs on brain cells and an individual’s susceptibility to certain psychiatric disorders, our study is the first to show that genetic susceptibility for a psychiatric disorder also involves these ancient viral DNA sequences.

It is still too early to determine the practical applications of our findings and whether they might lead to new treatments. However, by linking HERV expression in the brain with psychiatric disorders, their research highlights the importance of these mysterious sequences in the human genome, which have been overlooked for years.

There Is Hope – What to Do About It

In summary, there is so much we don’t know about our brain. Whilst we can not influence the genes we have been given, we have an incredible power to influence the factors that switch on or off a gene. Epigenetics is all about making the right decisions.

You have the privilege of choice every minute. Better nutrition, sleep, and an active lifestyle are waiting for you. Join me in becoming the best version of ourselves, one choice and one decision at a time!