When Autism Has no Known Cause

85% of autism is "idiopathic," meaning the cause is unknown.

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Known and Unknown Causes of Autism

When autism is of known origin (caused by a known genetic anomaly or exposure), it is referred to as "secondary autism." When autism is of unknown origin, it is called "idiopathic autism."

While there are over a dozen established causes of autism, most are very rare genetic disorders or prenatal exposures. As a result, approximately 85% of autism is "idiopathic." In other words:

  • a child is born to parents who are not autistic;
  • autism is not a known part of the child's family history;
  • the child was not premature;
  • the parents were under 35 years old;
  • tests did not uncover genetic anomalies (such as Fragile X syndrome) that might cause autism in the child;
  • the mother was not taking any of the drugs known to increase risk of autism while she was pregnant.

Might There Be a Shared Cause of Autism in Cases Where the Cause Is Unknown?

Theories abound regarding a possible "explosion" in the number of people with autism. After all, the steep increase in diagnoses does coincide with a steep increase in many environmental changes.  In fact, autism diagnoses increased at just about the same rate as:

  • cell phone use
  • ultrasound used to monitor fetal growth
  • cable television
  • video games
  • awareness of climate change
  • use of anti-tick and flea medications and shampoos for pets
  • number of vaccines given to young children
  • interest in organic and GMO foods
  • allergies to peanuts and gluten
  • prevalence of lyme disease

Could any or all of these changes in the world have contributed to or caused 85% of autism? There are certainly people who believe the answer is yes -- and most have picked out one or two of these potential causes to focus on.

The reality, however, is that autism presents itself differently in different people. This suggests a variety of causes -- and, perhaps, a variety of syndromes with some (but not all) symptoms in common. For example:

  • Autistic children were exposed to a huge range of environments, technologies, toxins, foods, and experiences.
  • Some seemed to have autistic symptoms almost from birth, while others appeared to regress after a year or more of seemingly normal development.
  • Some people with autism have severe symptoms, self-abusive or aggressive  behaviors, significant intellectual challenges, and no spoken language. Others are brilliant, articulate, and successful -- but also have social and communication challenges that make it difficult to make and keep relationships.
  • Some (but by no means all) present with a variety of symptoms in addition to the social communication, behavioral, and sensory challenges described in the diagnostic literature. For example, some have severe gastrointestinal issues; others have seizure disorders. Still others have serious problems with muscle tone.

If Your Child's Autism Is of Unknown Origin

If your child's autism is of unknown origin, there's very little you can do to change that reality.

So far as is known, however, having one child with autism does increase the likelihood that your next child may also be autistic. This is a concern to bear in mind when planning your family's future.

More About Causes of Autism:


National Human Genome Research Institute. "Learning About Autism." December 8, 2010.