Inheriting a Tendency to Brain Infection

Might some infectious diseases run in families because one inherits susceptibility to them? Although researchers generally agree that an individual's genetic makeup contributes in subtle ways to susceptibility to infectious disease, new findings from researchers in France support the controversial idea that an error in a single gene is enough to dramatically alter an individual's susceptibility to certain infections.

Howard Hughes Medical Institute (HHMI) international research scholar Jean-Laurent Casanova and Emmanuelle Jouanguy of the Necker Medical School in Paris, along with other colleagues, have identified a single gene that predisposes individuals to herpes simplex encephalitis, an infectious disease that tends to be extremely choosy about its victims. In a paper published in the September 29, 2006, issue of the journal Science, they describe two young patients who carry mutations in this gene who are susceptible to the disease while being otherwise immunologically normal. The paper was published in advance online.

As many as 8 out of 10 adults are infected by the herpes simplex virus. For most, the worst symptom is a cold sore, but in some individuals, the virus causes inflammation of the brain that can lead to mental retardation, epilepsy, or death. Until now, scientists have been unable to identify any specific risk factors for the disease.

Five years ago, Casanova began to suspect that those who were susceptible to the inflammatory brain disease were in fact genetically predisposed to it. There was little published evidence that herpes simplex encephalitis ran in families, which suggested to him that if a genetic element was at work, it was probably recessive: an individual had to carry two copies of the affected gene to show the predisposition.

Evidence he collected during an epidemiological survey in France supported that idea. The survey, conducted with pediatric neurologist Marc Tardieu of the Kremlin-Bic