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Like eating right and getting enough sleep, avoiding infection during pregnancy tops most women's lists as a good idea. New research is bolstering that common sense, revealing exactly how an infection could affect the cells in a child's brain well into adulthood.

Using mice as subjects, Dr. Freda Miller, a senior scientist in developmental and stem-cell biology at Toronto's Hospital for Sick Children and a professor in the department of molecular genetics at the University of Toronto, and her colleague, Dr. David Kaplan, discovered a major clue in the mystery of fetal brain development.

Miller and Kaplan found that a molecule the body produces as a common response to infection can cross the placenta and affect brain stem-cell formation in the fetus.

The pair measured a surge in brain stem-cell growth in mice born to mothers who had been injected with the molecule while pregnant.

Brain stem cells have been found to be crucial to cognition as well as the self-repair and maintenance of the adult brain. Previous research on mice has linked the responsible molecule, called "interleukin-6," to abnormal behaviour. Others have found that maternal infections are associated with autism and schizophrenia.

So this finding, which appeared Thursday in the online edition of the journal Cell Stem Cell, could be the missing link between infection and abnormal outcomes. It could also be the underpinning to all stem brain-cell development, says Miller.

Miller explains that the new study connects an environmental change in the womb to both positive and negative potential life-long effects. A case of influenza or measles while pregnant, for instance, could result in unwanted changes to the number and behaviour of brain cells. But staying healthy could have positive effects.

"We don't mean to frighten anyone," she says. "It means that if that fetus and mother are healthy, it is amazing for brain development."

And Miller's next area of interest is mapping how the immune response could interact with genetic predispositions in a fetus to determine whether a disordered gene for autism, for example, is switched on or not.

"We know it's not just about carrying one gene or another," she says. "It's not black and white, which is good. You're not fated to have 'x' happen to you," says Miller.