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What Causes Autism?

While there are many ideas in the lay community about the causes of autism, several decades of rigorous research appear to be narrowing the sources for autism spectrum disorders (ASD). It isn’t clear yet precisely which genes are responsible for any of the several conditions on the spectrum, but what is apparent is that these conditions have genetic factors. The article below explores these and other contributors to ASD.

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The Strong Case for Genes

Autism was first described in relation to a group of individuals with what is now called Down’s Syndrome. However, it wasn’t until the 1940s and 1950s that it was more appropriately applied to individuals who experienced social disabilities now known to be caused by neurological differences. While researchers devoted their energies for decades to understanding the suite of conditions that is now encompassed by the Spectrum, much of the diagnostic power of physicians is still based on symptoms. An individual is diagnosed based on observed differences in the brain and behavioral criteria.

What’s the current evidence for genetic roots of these disorders? In a review of current research published by Dialogues in Clinical Neuroscience, Dr. Pauline Chaste surmises several points. First, the likelihood that siblings with at least one parent contributing specific genes will also present with an ASD ranges from two to eight percent. However, she notes that variations of autistic traits are incredibly heritable—with the likelihood of presentation being as high as 40 to 80 percent. Identical twins with the inherited genes have a higher possibility of presenting with a fully developed ASD, the probability falling in non-identical and differently sexed twins as well as siblings.

However, she also highlighted the contention and lack of concurrence in the scientific community, based on the expansive gap in confidence level. Further on, the review notes that those with ASD present with a wide variation in language ability and cognitive development, which may indicate that environmental factors are important to consider, both in utero and postpartum.

Which Environment and What Factor?

When discussing this area of inquiry, it’s vital to first specify what isn’t meant. The persistence of the vaccine myth is both troubling and deadly, so it should be negated firmly at the outset. Vaccines do not and have never been shown to cause autism. However, this doesn’t mean that no environmental factor has a role to play. According to an article published in NPG Open Access, recent research indicates that women with Polycystic Ovary Syndrome (PCOS) may have a higher likelihood of bearing children with an ASD.

This startling concept pivots on the fact that women with this disorder—one in five, globally—have a consistently higher level of androgens in their system as a result of the cysts on their ovaries. They also possess a significantly higher level of anti-Mullerian hormone, which is typically found in higher levels in the male reproductive system. Because PCOS has received very little attention, researchers have only recently grasped its active role in influencing the development of fetuses and potentially activating genes that may contribute to ASD.

While the means by which ASD can be preemptively identified or prevented are still unrealized, the complexity of the causes has come into greater focus. What is clear is that environmental factors such as prenatal androgens and heritable genetic factors cannot be considered separately. Researchers must, instead, study the complex and interconnected dynamics of developmental context, genetic contribution, and heritability to more fully understand the causes of autism.