EVEN small amounts of a damaging chemical at a crucial stage in fetal development can lead neurons in an infant鈥檚 brain to commit suicide at accelerated rates. The new insight suggests that a single mechanism may lie at the heart of a wide spectrum of disorders, including fetal alcohol syndrome and schizophrenia.
The health effects of exposure to alcohol in the womb are well known 鈥� babies can develop anything from learning difficulties and memory problems to depression and psychosis in later life. But the mechanism was a mystery until 1999, when John Olner and his colleagues from Washington State University in St Louis discovered that alcohol slows down neuronal activity during the second half of pregnancy, a critical period of human fetal development. If the neurons don鈥檛 form the right connections during this time, they will die.
Now Olner鈥檚 team has found that in mice, even a single, low dose of alcohol can damage neurons. A blood level of 0.07 per cent, just below the legal driving limit in the US and UK, for only an hour, caused 4 times as many neurons to die as normal.
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Other studies in his lab have shown that different chemicals and exposure times destroy neurons in different areas of the brain. 鈥淲e view this as a common pathway that can give rise to a wide variety of disturbances,鈥� he says.
Another link between exposure to certain chemicals in the womb and a mental disorder comes from a recent epidemiological study by Ezra Susser and his colleagues at Columbia University in New York. They followed 12,000 people born between 1959 and 1966 whose mothers had given samples of blood serum while pregnant. They found that people exposed to high levels of lead in the womb were more than twice as likely to develop schizophrenia or similar disorders later in life. The results will be published in a future issue of Environmental Health Perspectives.
Although the link can鈥檛 be confirmed without larger studies, Susser points out that lead inhibits brain activity in exactly the same way as alcohol does. He believes cell suicide triggered by the lead is causing the schizophrenia.
If the connection is proved, it would be the first firm explanation for how conditions in the womb can trigger the illness. 鈥淚f we can understand even one pathway of how schizophrenia is caused, we could open up schizophrenia research to treatment and prevention,鈥� Susser says.
The work from the two groups presented to the AAAS also raises the tantalising possibility of explaining how apparently unrelated risk factors, such as poor nutrition or infection during pregnancy, can lead to mental disorders. Susser speculates that these factors too may trigger cell suicide by slowing down the activity of neurons at a crucial time. If there is a common mechanism, it would vastly simplify efforts to treat and prevent such disorders. 鈥淚t is possible,鈥� he says. 鈥淏ut it鈥檚 probably too much to hope for.鈥�