Pregant women subjected to traumatising stress are more likely to give birth to children who develop schizophrenia, according to a study published Thursday.
"The kind of stress in question are those that would be experienced in a natural disaster such as an earthquake or hurricane, a terrorist attack, or a sudden bereavement," explained lead author Dolores Malaspina, a researcher at New York University's School of Medicine.
Schizophrenia is a complex brain disorder, characterised by delusions and hallucinations, that usually strikes in late adolescence or early adulthood -- and with often devastating results.
They found that the offspring of women who were in their second month of pregnancy during the height of the Arab-Israel war in June of 1967 -- also known as the "Six Day War" -- showed a significantly higher rate of schizophrenia as they entered adulthood.
The study also highlighted a sharp difference in the impact on women and men.
Females who had been in their second month of fetal life during the conflict were 4.3 times more likely to develop the debilitating mental disease than women born at other times.
Males at the same stage of pre-natal life were only 1.2 times more likely to experience schizophrenia.
The researchers verified that other potential influences such as low birth weight or calorie intake had not played a role.
"It is a very striking confirmation of something that has been suspected for a long time," said Malaspina.
"The placenta is very sensitive to stress hormones in the mother. These hormones were probably amplified during the time of the war," she said.
The maximum period of impact occurred early in the gestation period, especially in the second month, said the study, published in the Britain-based open access journal BioMed Central Psychiatry.
Earlier research has also shown that schizophrenia can follow intrauterine stress.
One study looked at the impact of bereavement, comparing the offspring of mothers in Finland whose husbands died during their pregnancy with similarly bereaved women whose partners died after delivery.
The incidence of schizophrenia was considerably higher in the first group, especially when the husband's death occurred early in gestation.
"There is overwhelming experimental evidence that stress to pregnant mammals alters neurodevelopment in the offspring and affects their subsequent behavior, both in childhood and as adults," Malaspina concluded.
"The knowledge that maternal stress affects the fetus has important implications for mental health in a world threatened by acute violence and war," she said.
Schizophrenics often hear voices, and may believe that other people are reading their minds or controlling their thoughts.
These frightening experiences can cause social withdrawal and extreme agitation.
There is no known cure for the chronic disorder, which affects approximately one in 200 people, emerging in men in their late teens and early 20s, and a decade later in women, according to the World Health Organisation.