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According to statistics from the Centers for Disease Control (CDC), the prevalence of autism spectrum disorder (ASD) increased nearly 120 percent from 2000 to 2010—from 1 in 150 children to 1 in 68. It is the fastest-growing developmental disability, with a 10-17 percent increase annually in recent years.

Facing such a dramatic reality, researchers are hard at work trying to understand this brain development disorder. As points out, there is no one cause of autism just as there is no one type of autism.

Scientific advances over the past decade have shown us that most cases arise from a complex combination of genetics and environmental influences. A small number are associated with a single rare gene mutation, but, in general, there is a genetic predisposition arising from the combinations of thousands of genes, which is acted upon by environmental factors.

New research suggests that one of those environmental factors may be a commonly used pain medication taken during pregnancy.

“A new study has found that paracetamol (acetaminophen), which is used extensively during pregnancy, has a strong association with autism spectrum symptoms in boys and for both genders in relation to attention-related and hyperactivity symptoms.”

The findings were published this week in the International Journal of Epidemiology. This is the first study of its kind to report an independent association between the use of this drug in pregnancy and autism spectrum symptoms in children. It is also the first study to report different effects on boys and girls. Comparing persistently to nonexposed children, the study has found an increase of 30 per cent in the risk of detriment to some attention functions, and an increase of two clinical symptoms of autism spectrum symptoms in boys.

If further research confirms this to be the case, it would be a shocking development, as Tylenol (acetaminophen) is the most commonly used medication during pregnancy.

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Recommended for You acknowledges that the “drug hasn't been well studied in pregnant women,” but also notes that extensive use, especially in the later months of pregnancy, is possibly linked to behavioral problems.

The website also notes that fevers during pregnancy can cause risks to the developing baby, so there is a careful balance between controlling fevers and minimizing over-the-counter pain relief/fever reduction medications.

"Co-author Dr. Jordi Júlvez, also a researcher at CREAL, commented on the possible reasoning for the effects of paracetamol on neurodevelopment: "Paracetamol could be harmful to neurodevelopment for several reasons. First of all, it relieves pain by acting on cannabinoid receptors in the brain. Since these receptors normally help determine how neurons mature and connect with one another, paracetamol could alter these important processes. It can also affect the development of the immune system, or be directly toxic to some fetuses that may not have the same capacity as an adult to metabolize this drug, or by creating oxidative stress."

The researchers note that more studies should be conducted to better understand the risks of acetaminophen use during pregnancy and brain development risks.

Regarding the factor of genetic predisposition to ASD among populations, recent research has revealed that autism genes actually exist in all of us.

“With recent advances in genome sequencing and analysis, a picture of ASD's genetic landscape has started to take shape. Research has shown that most ASD risk is polygenic (stemming from the combined small effects of thousands of genetic differences, distributed across the genome). Some cases are also associated with rare genetic variants of large effect, which are usually de novo.

"There has been a lot of strong but indirect evidence that has suggested these findings," said Dr Mark Daly, co-director of the Broad Institute's Medical and Population Genetics (MPG) Program and senior author of the study.

"Once we had measurable genetic signals in hand -- both polygenic risk and specific de novo mutations known to contribute to ASD -- we were able to make an incontrovertible case that the genetic risk contributing to autism is genetic risk that exists in all of us, and influences our behavior and social communication."