A new study of the origins of autism lends support to a controversial treatment using a blood pressure drug, it is claimed.

Scientists found that injecting pregnant mice with bumetanide reduced abnormally high levels of chloride in the brains of their unborn babies.

This activated a neural switch that prevented nerve cells becoming over-excited – believed to be one of the underlying causes of autism.

Since there is no way to screen for autism in human foetuses, the same treatment could not be given to human pregnant mothers.

But a controversial trial has previously suggested that bumetanide can improve social behaviour in children from the age of three with mild forms of autism.

After three months on the drug, the 27 children aged three to 11 had better autism symptom scores than children taking a dummy placebo.

Children with severe autism did not appear to benefit, according to the results published last year in the journal Translational Psychiatry.

Although the study attracted criticism from a number of experts who doubted its significance, its authors say the new research vindicates their approach.

The findings, reported in the journal Science, indicate that under normal circumstances the hormone oxytocin regulates chloride levels at birth and protects against autism.

Oxytocin, known as the “love hormone”, also plays a crucial role in forging the bond between mother and child.

Yehezkel Ben-Ari, director of the Mediterranean Institute of Neurobiology at the INSERM research organisation in Paris, France, who led both studies, said: “These data validate our treatment strategy, and suggest that oxytocin, by acting on the chloride levels during delivery modulates/controls the expression of autism spectrum disorder.”

Bumetanide tablets are normally prescribed to remove excess fluid from the body and reduce pressure within blood vessels.

The research may also have implications for Caesarean deliveries, which have been said to disrupt mothers’ oxytocin levels.

“Although it is true that epidemiological data suggesting that scheduled Caesarean deliveries may have increased the incidence of autism are controversial, it nonetheless remains that these studies should be followed up and extended in order to confirm or refute this relationship, which is still possible,” said Ben-Ari.

“To treat this type of disorder, it is necessary to understand how the brain develops and how genetic mutations and environmental insults modulate brain activity in-utero (in the womb).”

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