What Causes Autism?

What causes autism

You may have heard the term “autism spectrum disorder” bandied about more lately and wondered what causes autism. The fact is that the incidence of this disorder has increased ten-fold in the last 40 years. What is the disease and what causes autism?

What is Autism?

The Oxford Dictionary defines autism as a “condition affecting brain development that can be severe or mild.  People with autism can find it difficult to communicate and form relationships and may show repeated or limited patterns of thought and behavior.”  Recently, the Diagnostic and Statistical Manual of Mental Disorders (DSM-5) published by the American Psychiatric Association combined all types of autism under one diagnosis, including Asperger’s Syndrome and “unspecified” in the designation. The website Autism Speaks characterizes autism spectrum disorder as a group of disorders of brain development.  You might also be asking, “Is autism rare?”  According to the Centers for Disease Control, one in 44 children is affected by autism.

The most obvious signs that a child is autistic begin to emerge between two and three years of age.  There are more boys with the disorder than girls. Today, there are approximately three million people in the United States who have been diagnosed as being on the autism spectrum.

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See Also: What are the 10 Most Common Signs of Autism Spectrum Disorder (ASD)?

A Historical Look at Autism Spectrum Disorder (ASD)


The description of autism has come a long way since it was first described as a psychiatric condition back in 1943.  In 1987, the DSM-III made changes that indicated autism could not be confined to a single condition, but a spectrum of different conditions.  The DSM-IV went further to categorize autism as five different conditions with distinct features.  These include:

  • Pervasive Developmental Disorder Not Otherwise Specified (PDD-NOS) – this diagnosis was for individuals on the spectrum but who didn’t meet the full diagnostic criteria for another ASD.
  • Autistic Disorder – This is what most people think of when they think about autism.  It falls somewhere between PDD-NOS and Asperger’s.
  • Rett’s Syndrome – A genetic disorder that can cause loss of spoken language and motor skills along with other neurological problems.  It is a rare disorder that occurs almost exclusively in girls.
  • Childhood Disintegrative Disorder- CDD is another unusual disorder.  These children appear normal in development until sometime between their second and fourth birthdays, when they begin to deteriorate and display severe developmental regression.
  • Asperger’s Syndrome was the highest functioning disorder on the spectrum. These children are often misdiagnosed as having ADD or obsessive-compulsive disorder. They are resistant to change, but usually highly intelligent and talented in one or more areas that they focus on to the exclusion of others. Some researchers believe Einstein had Asperger’s.

What is the Autism Spectrum?

The DSM-5 utilized the term autism spectrum disorder.  This term refers to the many kinds of autism and to the extent to which it impairs functioning. This term makes sense because the symptoms seem to overlap at times and may be more, or less severe. One therapist defined the spectrum as a rainbow where the colors seem to mix as they met. Individuals with autism spectrum disorders have persistent deficits in social communication and social interaction.  These deficits are evident regardless of their environment.  Autistic individuals have deficits in:

  • social-emotional reciprocity
  • nonverbal communicative behaviors used for social interaction
  • developing, maintaining, and understanding relationships

When thinking about autism as a spectrum, it is important to recognize that these deficits vary in severity from one individual to the next.

Individuals with autism also display restricted, repetitive patterns of behavior.  They may have very focused interests or activities that they enjoy.  According to the most recent DSM, an individual must have at least two of the following (either currently or historically) to be considered for an autism diagnosis.

  • Stereotyped or repetitive behaviors including motor movements, use of objects, or speech
  • An intense desire for sameness including inflexibility to changes in routine.
  • Restricted or fixated interests that are not typical in intensity or focus
  • Hyper or hypo reactivity to sensory input or sensory aspects of their environment

What Causes Autism Spectrum Disorder?

That brings us to the initial question: what causes autism? Before recent advances, the answer to this question was “who knows?” New research seems to indicate there is no one cause. Research suggests autism is caused by a combination of:

  • genetics
  • environmental factors


There is research that shows that autism runs in families, indicating a genetic link.  Rare genetic mutations have been identified, but it appears that the disorder is not caused by any one mutation, but by a combination of genetic factors and environmental issues. Some children seem to have a genetic disposition to autism. In fact, in a study of twins, it was discovered that if one twin displayed autism symptoms, then the likelihood that the other twin would develop autism was 36-95 percent.

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Other research suggests children may inherit DNA mutations from their fathers.  Until recently, it was believed that mothers were responsible for autism DNA mutations.

In a multinational study of more than two million individuals, researchers found evidence that links inherited genetic influences to autism spectrum disorder.  Obviously additional research is needed to study any correlations between other autism risk factors and genetics.

Environmental Factors

There is some research that indicates certain environmental factors could put individuals at higher risk for developing autism.  Some of these include:

  • Advanced parental age at conception
  • Children whose mother was ill during pregnancy or were obese
  • Difficulty during the birth, especially oxygen deprivation
  • Children who were born prematurely or had a very low birth weight

While these factors alone do not cause autism, they can increase the risk when paired with other genetic or developmental factors.  Another thing scientists are investigating as a possible link to autism is an immune system dysfunction that causes neuroinflammation.  This neuroinflammation bas been found in some individuals with ASD, suggesting the symptoms associated with autism may be triggered by this inflammation.

There is also evidence that supports exposure to air pollution as a risk factor for autism spectrum disorder.  Children born to mothers living near a freeway during the final trimester of their pregnancy are twice as likely to be diagnosed with ASD.  There is also research that suggests that children with a mutated MET gene who have elevated levels of exposure to air pollution are also at a higher risk for ASD.

Vaccines and Autism

One of the biggest controversies related to the cause of autism spectrum disorders is whether or not routine childhood vaccines can cause autism.  There is no current, reliable study that shows a definitive link between autism and vaccines.  In fact, not getting vaccinated out of fear that doing so would cause autism can actually increase the risk of catching diseases like measles or mumps.  If you have concerns, this is an important discussion to have with your child’s pediatrician.


Autism Spectrum Disorder Cause

The question, “What causes autism spectrum disorder?” doesn’t have a clear-cut answer…just yet.  What causes autism seems to be a combination of factors, and not any single thing. While it is too early in research to say for certainty what causes autism, most researchers have been definite in what does not cause it: parental actions or immunizations.

If your child, or the child of someone you know, has been diagnosed with autism, there are treatments available. Although there is no cure, some children’s symptoms seem to abate over time. In time, research will reveal what causes autism, and we can work on a cure, or at least significant interventions.

Related Resource: 5 Ways To Communicate With Children With Autism