New research suggests that infectious diseases may run in families. Investigators say the discovery represents a major shift in the way scientists view human disease.
Experts have always accepted that certain chronic illnesses run in families. But French researchers now say they have the first evidence that susceptibility to an infectious disease can be inherited.
The investigators focused on herpes simplex, a virus that infects eight out of 10 adults. In most people, the worst symptom is a painful cold sore.
But in a small percentage of infected people, herpes simplex causes a potentially devastating brain disease called viral encephalitis. The disease can cause epilepsy, mental retardation and death.
French researchers studying the families of children with viral encephalitis found a defect in an important protein that signals the immune system to recognize foreign invaders. Both the children and a number of their family members had normal immune systems but they also had a flawed copy of the gene that produces that signaling protein, type-1 interferon.
In a study published in the journal Science, the researchers describe the case of two French children with viral encephalitis who had inherited a defective copy of the signaling gene.
Researcher Jean-Laurent Casanova of the Necker Medical School in Paris says, until now, experts wondered why viral encephalitis appeared to run in families. Now they know why.
"We have solved this sort of enigma or mystery by showing that the rare individuals who develop encephalitis have genetic lesions, genetic defects in a molecular circuit that is required for the production of other molecules that are required for anti-viral immunity," explained Casanova.
Casanova says there may be any number of infectious diseases that run in families that can be traced to genetic defects.
"This is a paradigm shift in the field of infectious diseases which should now in my opinion not only be considered from the angle of the invading microorganism, whether a virus or a bacterium, but from the angle of the genetic make-up of the infected individuals," he said.
Casanova says it is possible that children who develop viral encephalitis may soon be treated with interferon along with the standard herpes drug, acyclovir.
He expects that in the future, defective genes will be identified and corrected in people who might otherwise become critically ill from harmless bacteria and viruses.