It’s human nature to seek answers, especially to questions that involve the health and well-being of those we love, particularly our children. But there are still sol many medical mysteries science has yet to answer — and the exact cause of autism spectrum disorder is one of them.

Autism spectrum disorder is a complex condition with symptoms that present in a variety of combinations and levels of intensity and, given this, experts believe there are probably many causes, with both genetics and environment likely playing a role.

Genetic factors that may contribute to the cause of autism The research into the genetic causes of autism offers great insight into not just the way that the bodies and brains of people affected by ASD work, but also into the role family history in predicting vulnerability to autism spectrum disorder.

Specific genes may be the cause of autism: Researchers have identified several genes that are associated with autism spectrum disorder. Brain imaging studies of people with ASD have shown differences in the development of several regions of the brain in people with autism. And there are studies that suggest autism could be caused by disruptions in normal brain growth very early in development and that these disruptions could be caused by defective genes, including those that control brain development and brain cell communication.

We also know that many of the genes that have been shown to be associated with autism are involved with the chemical connections between brain neurons (synapses), which is a promising avenue of research in treating and curing, if not preventing, autism spectrum disorder.

Family history may give clues to the cause of autism: It’s also worth looking at the full family tree when discussing the root cause of autism. Twin and family studies have provided evidence that some people likely have a genetic predisposition to autism. In identical twins, the odds of both twins having autism spectrum disorder if one does are 36-95 percent. And in families that have one child with ASD, the risk of future children also being affected by the disorder increase. What’s more, sometimes parents and other relatives of children with ASD exhibit mild social communication skill issues or engage in repetitive behaviors—both of which are classic symptoms of ASD.

There is also evidence to suggest that emotional disorders like bipolar disorder and schizophrenia are more common in the families of people with autism spectrum disorder.

But the cause of autism can also be spontaneous and random: While we know that many inherited genes are linked to autism, recent research has also shown that de novo—or spontaneous—gene mutations can contribute to the development of autism spectrum disorder. These mutations occur spontaneously in a parent’s sperm or egg cell or during fertilization and then occur again in each cell as the fertilized egg divides. While some of these mutations impact single genes, others, known as “copy number variations,” involve stretches of DNA containing multiple genes being copied or deleted.

According to recent research, people with autism spectrum disorder tend to have more of these “copy number variations” than people without ASD, which suggests that it isn’t the gene mutations, but the spontaneous copying of those mutations across multiple genes that may cause autism. de novo gene mutations than those without the disorder, suggesting that for some the risk of developing ASD is not the result of mutations in individual genes but rather spontaneous coding mutations across many genes.

Environmental factors that may contribute to the cause of autism When it comes to potential environmental factors involved in the cause of autism, most that have been identified involve events and circumstances present before or during birth, including: - Parental age at the time of conception—the risk of developing autism is higher in children born to older parents. - Parental age at the time of conception—the risk of developing autism is higher in children born to older parents. - Prenatal exposure to air pollution or certain pesticides - Maternal obesity, diabetes, or immune system disorders - Extreme prematurity or very low birth weight - Birth difficulties leading to periods of oxygen deprivation to the child’s brain

Factors that do not cause autism While scientists don’t yet know the exact cause of autism spectrum disorder, they have identified some factors that don’t contribute to the development of ASD, including: - Parental practices—the theory that parenting choices lead some children to develop ASD has been disproved by scientists. - Vaccinations—contrary to claims made by some vocal opponents of childhood vaccinations, these have been shown to have no impact on the risk of autism spectrum disorder.