Exposure to high levels of oestrogen sex hormones in the womb has been linked to a greater likelihood of developing autism, according to a study* published in Molecular Psychiatry.
In 2015, the researchers at the University of Cambridge and the State Serum Institute in Denmark measured the levels of four prenatal steroid hormones, including two known as androgens, in the amniotic fluid in the womb and discovered that they were higher in male foetuses who later developed autism. These androgens are produced in higher quantities in male than in female foetuses on average, so might also explain why autism occurs more often in boys. They are also known to masculinise parts of the brain, and to have effects on the number of connections between brain cells.
More recently the same researchers tested the amniotic fluid samples from the same 98 individuals sampled from the Danish Biobank, which has collected amniotic samples from over 100,000 pregnancies, but this time looking at another set of prenatal sex steroid hormones - oestrogens. This is an important next step because some of the hormones previously studied are directly converted into oestrogens.
All four oestrogens were significantly elevated, on average, in the 98 foetuses who later developed autism, compared to the 177 foetuses who did not. High levels of prenatal oestrogens were even more predictive of likelihood of autism than were high levels of prenatal androgens (such as testosterone). Contrary to popular belief that associates oestrogens with feminisation, prenatal oestrogens have effects on brain growth and also masculinise the brain in many mammals.
Professor Simon Baron-Cohen, director of the Autism Research Centre at the University of Cambridge, who led this study and who first proposed the prenatal sex steroid theory of autism, said: "This new finding supports the idea that increased prenatal sex steroid hormones are one of the potential causes for the condition. Genetics is well established as another, and these hormones likely interact with genetic factors to affect the developing foetal brain."
Dr Alexa Pohl, part of the Cambridge team, said: "This finding is exciting because the role of oestrogens in autism has hardly been studied, and we hope that we can learn more about how they contribute to foetal brain development in further experiments. We still need to see whether the same result holds true in autistic females."
*Baron-Cohen S, Tsompanidis A, Auyeung B, et al. Foetal oestrogens and autism. Molecular Psychiatry, 29 July 2019. DOI: 10.1038/s41380-019-0454-9