A drug that causes a high rate of fetal malformations… What is it?

In a study of mice and human tissue, scientists discovered that valproic acid traps some stem cells in a suspended state where they cannot grow or divide properly.

By forcing master stem cells into this state, valproic acid may disrupt brain development in the womb, thus causing cognitive and developmental disorders, according to the study published in the journal PLoS Biology.

In their report, the study authors noted that an estimated 30 to 40 percent of children exposed to the drug in utero develop cognitive impairment or autism spectrum disorder.

In a subset of affected children, exposure to valproic acid can also cause birth defects outside the brain, including heart abnormalities.

Subsequent research in rodents and monkeys indicated that when the drug is taken in the first few weeks of pregnancy, it may disrupt the early stages of nervous system formation.

“We exposed mouse embryos to the drug,” says Bill Keys, team leader at the Institute of Genetics, Molecular and Cell Biology in Strasbourg. “The neural tubes of these embryos often failed to close, and later in development, embryonic mice also developed unusually small heads and brains.”

As part of the experiment, the team exposed mice to high doses of valproic acid over a short period of time, while in real life, patients would take a lower dose of the drug over a longer period of time.

Keys said the short-term high-dose regimen in the trials may have produced an “exaggerated” effect in mice, which would not necessarily match in human fetuses.