Could a viral infection you experience today cause mental health disorders for generations of your descendants? Absolutely. Many psychological disorders are driven by a viral infection in prehistoric times that disrupted DNA and has been passed down through generations.

Viruses survive as genetic parasites because they must infect healthy cells to reproduce. Viruses hijack the host’s genetic operation because they do not have the cellular machinery to make their own proteins.

Dreadful cancers and other illnesses can be caused by viral infection, but less widely appreciated is that DNA that was inserted into the genome of our ancient human ancestors from viral infection can cause psychological and neurological disorders through generations.

Briefly, here is the diabolical way viruses hack into our genes.

Retroviruses, like HIV, infect cells and inject their genetic material, RNA, into the host cell. The viral RNA is converted to DNA and inserted into the infected cell’s genome like malicious software code infecting a computer program. When the cell reads that foreign DNA code, it unwittingly generates viral proteins and produces swarms of the virus.

This viral genetic sabotage is a reversal of the normal operation that cells use to make a specific protein needed for cell structure and function. Normally, the instructions to make a particular protein are coded in a stretch of DNA, which is a durable genetic blueprint locked inside the cell’s nucleus.

A copy of the DNA instructions for a gene is made by a string of RNA that leaves the nucleus to deliver the information to the cell’s machinery that synthesizes the protein specified. Like a Post-It note, RNA is a short-lived molecule meant to jot down information temporarily. The RNA is quickly discarded so that the cell does not get bogged down by outdated information, while the master blueprint is preserved inside the cell nucleus. By converting its viral RNA into DNA, the infecting virus reverse-engineers the normal process. That, however, can cause long-lasting genetic haywire.

The viral DNA is often inserted into long stretches of DNA that do not code for genes, but are instead regions of DNA, called introns, that control the switching synthesis of a gene on or off. Only 2 percent of the human genome is genes, and the rest of the DNA controls when a gene is produced. Fouling up the intricate control of gene production can wreak havoc on a cell. These ancient bits of viral DNA stuck inside our genome are known as endogenous retroviruses (ERVs), and they comprise 8 percent of human DNA.

Multiple sclerosis, amyotrophic lateral sclerosis (ALS), Parkinson’s, Alzheimer’s disorder, and other neurological and cognitive disorders are known to be triggered by ERVs. A growing number of studies link these retroviral DNA elements with neurodevelopmental and psychiatric disorders.

Autism spectrum disorder (ASD) patients have significantly higher levels of a particular ERV (HERV-H), compared to healthy children. Similar findings have been found for other ERVs, and some other ERVs (HERV-W) are unusually scarce in children with ASD.

Abnormal ERVs have also been identified in schizophrenia, a major psychiatric disorder affecting up to 1 percent of the world’s population. Some 29 percent of people with recent-onset schizophrenic disorder have snippets of HERV-W in their cerebrospinal fluid. Abnormal ERV appearance has also been identified in people with bipolar depression. Postmortem analysis of the brains of people with schizophrenia and several other mental disorders shows abnormal traces of ancient viral genes (ERVs) in brain regions known to be disrupted in the psychiatric disorder.

This new information expands understanding of the biological basis of mental illnesses, but it is important to recognize that our fate is not necessarily cast at birth by our genes. As in most things in biology, health and illness result from interactions between genes and the environment. Stress, environmental toxins, and inflammation can activate ERVs.

It is startling to realize that what we believe to be the most complicated structure in the known universe, the human brain, can be undermined by the most primitive form of life—a virus that has parasitized human DNA over eons.