The idea is that some infection, possibly early in childhood, somehow interferes with the body's control of the old viral DNA and allows it to express itself. This might explain why schizophrenia is more common in people born in early spring, and why it is often associated with inflammation:
The facts of schizophrenia are so peculiar, in fact, that they have led [Dr. Fuller] Torrey and a growing number of other scientists to abandon the traditional explanations of the disease and embrace a startling alternative. Schizophrenia, they say, does not begin as a psychological disease. Schizophrenia begins with an infection.
The idea has sparked skepticism, but after decades of hunting, Torrey and his colleagues think they have finally found the infectious agent. You might call it an insanity virus. If Torrey is right, the culprit that triggers a lifetime of hallucinations—that tore apart the lives of writer Jack Kerouac, mathematician John Nash, and millions of others—is a virus that all of us carry in our bodies. “Some people laugh about the infection hypothesis,” says Urs Meyer, a neuroimmunologist at the Swiss Federal Institute of Technology in Zurich. “But the impact that it has on researchers is much, much, much more than it was five years ago. And my prediction would be that it will gain even more impact in the future.”
Very interesting. I think it will turn out that many of our most mysterious health problems are caused by various kinds of infections, and our bodies' responses to them.
Through this research, a rough account is emerging of how HERV-W could trigger diseases like schizophrenia, bipolar disorder, and MS. Although the body works hard to keep its ERVs [viral DNA strands] under tight control, infections around the time of birth destabilize this tense standoff. Scribbled onto the marker board in Yolken’s office is a list of infections that are now known to awaken HERV-W—including herpes, toxoplasma, cytomegalovirus, and a dozen others. The HERV-W viruses that pour into the newborn’s blood and brain fluid during these infections contain proteins that may enrage the infant immune system. White blood cells vomit forth inflammatory molecules called cytokines, attracting more immune cells like riot police to a prison break. The scene turns toxic.
In one experiment, Perron isolated HERV-W virus from people with MS and injected it into mice. The mice became clumsy, then paralyzed, then died of brain hemorrhages. But if Perron depleted the mice of immune cells known as T cells, the animals survived their encounter with HERV-W. It was an extreme experiment, but to Perron it made an important point. Whether people develop MS or schizophrenia may depend on how their immune system responds to HERV-W, he says. In MS the immune system directly attacks and kills brain cells, causing paralysis. In schizophrenia it may be that inflammation damages neurons indirectly by overstimulating them. “The neuron is discharging neurotransmitters, being excited by these inflammatory signals,” Perron says. “This is when you develop hallucinations, delusions, paranoia, and hyper-suicidal tendencies.”