A new study found that boys with autism are more likely to have been exposed to higher hormone levels in the womb than those who normally develop.

Dr. Michael Lombardo and Prof. Simon Baron-Cohen in Cambridge, Prof. Bent Norgaard-Pedersen in Denmark and their team warn that while the new study may aid in explaining why autism is more common in boys than girls, people should not use it to screen for the condition.

Researchers used some stored samples of amniotic fluid from Danish women who had amniocentesis from 1993 to 1999. Amniocentesis is the drawing of small amounts of fluid from the sac, offered to pregnant women who have an increased risk of having an infant with birth defects.

University of Cambridge and Statens Serum Institute scientists analyzed the hormone levels of almost 20,000 samples and compared the samples from 128 boys with autism with samples from 217 boys without it. The girls were excluded because only a few had autism and other issues made it hard to compare levels of steroid hormones between girls with autism and girls developing normally.

The 128 boys specifically had elevated sex hormone levels such as progesterone, testosterone and stress hormone cortisol. Why the hormone levels are elevated is still unclear, but researchers think it could be a genetic problem. The team explained that the hormones were in the amniotic fluid surrounding the infant in the womb and these are more likely from the infant than the mother. Further tests will be done on the mother's hormones to establish the theory.

The study findings may help researchers discover some of the main causes of autism and figure out why males are four or five times more at risk to be diagnosed with autism which affects about one percent of the human population.

"In the womb, boys produce about twice as much testosterone as girls, but compared with typical boys, the autism group has even higher levels. It's a significant difference and may have a large effect on brain development," director Simon Baron-Cohen of the Autism Research Centre at Cambridge University said.

Only boys were tested in the early phase of the study and the next step is to test the girls to see if the same telltale signs exist for them as well. Autism is a wide spectrum of disorders and an estimate of one in 100 children may be affected by it. The condition affects the child's speech, learning and social interaction.

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