What Causes Autism? 6 Possible Triggers + Common Comorbid Conditions

It’s no secret that the frequency of autism diagnosis has increased dramatically since the 1980s. The most recent CDC report indicates one in every 59 children is diagnosed with autism, which shows a 15% increase from the report before. Boys are much more likely to be diagnosed than girls, and the statistic varies by location. 

As American autism rates rise and public awareness heightens, many are asking, “what causes autism?” Furthermore, is there anything that we can do to guard against the risk factors? 

While the exact causes of autism aren’t fully understood, there are many studied triggers and environmental risk factors that we have discovered to contribute to autism spectrum disorder. 

The Centers for Disease Control and Prevention (CDC), American Academy of Pediatrics, and others are tracking this disorder closely and searching for answers. We’ve compiled the most compelling research for you below.

What is autism?

The American Psychiatric Association has redefined this condition several times. The most current criteria was released in 2013 and is used by doctors today. While many conflate intellectual disability with all autism, the term is more complex and varied than that. 

The symptoms of autism begin early in life, continue after childhood, and can interfere with daily life. In many cases, behavioral symptoms are evident within the first year of a child’s life. Each case of autism is individual and presents differently, but there are many common symptoms that may be recognizable. Here are the most prevalent autism symptoms.

An individual with autism spectrum disorder will have six or more identifiers from these three major categories:

Social Interaction Impairments

  • Failure to use eye contact, body posture, facial expression
  • Failure to develop peer relationships
  • Lack of social interaction, sharing, or enjoyment with others
  • Lack of social or emotional reciprocity

Communication Impairments

  • Delay or total lack in speech development
  • Inability to initiate or maintain conversational speech
  • Stereotyped or repetitive use of language

Repetitive and Stereotyped Behaviors, Interests, and Activities

  • Abnormal intensity or focus on stereotyped or restricted patterns of interest
  • Inflexible adherence to rituals and routines
  • Repetitive movements (hand-flapping, finger flicking or twisting, or complex body movements)
  • Preoccupation with parts of objects

These behavioral indicators are used for diagnosis of autism, but what causes autism in the first place? Many genetic factors and environmental factors can put children at a greater risk, though we aren’t aware of one single cause. We still have much to learn about autism, one of the most pervasive developmental disorders of our time.

Types of Autism

Autism spectrum disorder has had many names over the years and in recent years has become more of an umbrella term over a spectrum of behaviors. Autism itself can vary from mild to severe, based in part on how much support is needed for the patient, as well as behavior and social interaction skills. 

Autism spectrum disorder is one category of varied behavior. It was distinguished in 2013 as a more broad classification that includes three diagnoses which were previously considered separate. The most obvious is Autistic Disorder, also known as autism, childhood autism, early infantile autism, Kanner’s syndrome, or infantile psychosis. 

Two more conditions now fall into ASD’s umbrella. Asperger Syndrome, also known as Asperger’s disorder, was previously categorized as separate from autism spectrum disorder. Finally, this diagnosis includes Pervasive Developmental Disorder (Not Otherwise Specified), also known as atypical autism and previously classified separately as well.

The most current definition of autism includes five subtypes within autism spectrum disorder: 

  1. With or without accompanying intellectual impairment
  2. With or without accompanying language impairment
  3. Associated with a known medical or genetic condition or environmental factor
  4. Associated with another neurodevelopmental, mental, or behavioral disorder
  5. With catatonia

Those with autism may fall into one or more of these subtypes.

6 Possible Causes of Autism

The exact cause of Autism Spectrum Disorder is unidentified. The most current research indicates that there is no individual cause, but several factors may increase autism risk. Despite the lack of a simple explanation, genetic and environmental factors can be traced to the development of the condition. 

Here are five possible causes of autism that have been scientifically linked to ASD.

1. Genetics: Disorders, Mutations, and Epigenetics 

Genetic factors are commonly agreed upon as a risk factor for autism. In fact, one of many twin studies suggests that “autism is under a high degree of genetic control.” While genetics and genetic disorders alone don’t cause autism, they seem to be a major contributing factor as autism follows an inheritance pattern.

For instance, having a sibling with autism raises children’s odds of being diagnosed as well — likely due to similar genetic backgrounds. 

Genetic mutations and birth defects like fragile X syndrome, tuberous sclerosis, or Rett syndrome are suspected to be causes for autism as well. The mutations found in these conditions can be genetic causes for the behavioral disorder as they progress. These genetic mutations can affect body and brain in a way that contributes to the development of ASD. 

For example, there’s strong evidence that the higher brain deterioration in Rett syndrome contributes to autism, as does the way fragile X syndrome affects neurons. The TSC gene mutation found in tuberous sclerosis can cause autism if it occurs during critical junctures in brain development. 

Research indicates that these conditions don’t just happen alongside autism, but genetically add to the likelihood of developing it.

More recently, research on impaired methylation from a mutation of the MTHFR gene found this mutation is also associated with higher rates of ASD. Scientists hypothesize that oxidative stress and impaired methylation from this mutation contribute to autism. These are environmental factors, but it’s believed that genetic factors make these problems more likely

Glutathione, the body’s primary antioxidant and detoxification agent, is produced less efficiently with impaired methylation. This subjects the body to more oxidative stress and tissue damage from free radicals, which would normally be neutralized by antioxidants like vitamins C and E. It also means the body has a harder time detoxing environmental chemicals (which I discuss below).

These genetic issues also impair mitochondrial function, the part of cells responsible for producing ATP for energy. Fortunately, all of these are testable functions and can be offset somewhat by diet and supplementation changes.

Another area of emerging science that may play a part in the development of autism is epigenetics. Unlike your genes, your epigenetics are changeable — alterations in your diet, lifestyle, and other contributing factors can change which genes are expressed and to what extent. Epigenetic changes result in epigenomics, in which your entire genome is programmed to express differently than before.

For ASD, the most significant epigenetic changes are those that occur while in the womb. The epigenetic changes associated with autism include, so far:

  • Maternal influenza infection during pregnancy 
  • Prolonged maternal fever during pregnancy
  • Maternal asthma during pregnancy

2. Environmental Chemicals

Due to modern farming and food production methods (as well as the use of medications and vaccinations during childhood), children are often exposed to chemicals that can influence the development of autism. Other factors contribute here as well, like chemicals found in plastics we use every day.

These include:

  • Heavy metals, such as arsenic, cadmium, mercury, and lead
  • Pesticides and insecticides like organophosphate and glyphosate (Roundup)
  • Neurotoxicants including PCB (polychlorinated biphenyls) and PBDE (polybrominated diphenyl ether)

All of these are strongly linked to the development of ASD. It’s not a surprising notion — all of these chemicals interact with the central nervous system, as well as other related bodily systems. They are thought to be most problematic when other risk factors are also present for autism.

3. Certain Drugs and/or Vaccines

Some prescription drugs have been linked to a higher incidence of autism. Specifically, valproic acid taken during pregnancy increase the likelihood of an autistic child. Prenatal usage of these drugs should be limited in order to protect the health of the fetus.

Valproate, an antiepileptic drug that includes valproic acid, was likely to hurt the child, even if the mother didn’t experience seizures. While it’s known to cause malformations in children, evidence suggests that even without these additional concerns, the rate of autism diagnosis in children exposed to valproate is raised.

A large number of studies have also shown that SSRIs (a type of antidepressant) used during pregnancy may also increase the risk for autism. One review estimates the risk is increased by 1.53 times when antidepressants are taken by a pregnant mother, 1.48 times when taken immediately before conception, and even 1.29 times with paternal use of antidepressants before conception.

The risk of stopping medications during pregnancy is also significant, particularly with antidepressants. Medical counsel and great care should be used in choosing what prescription drugs to use while pregnant — do not stop taking prescribed medications unless you’ve discussed it with your physician. 

Once a child has been born, it also seems that the use of acetaminophen may impact the risk level for ASD. Fever management hasn’t caught up with the available science — using fever-lowering medications is rarely beneficial to children, but it’s still a very common practice among parents and even pediatricians.

The use of acetaminophen (Tylenol) seems to the endocannabinoid system, lowering its activity in those with ASD. Another fascinating point of the study where this is noted: When children with ASD develop a fever, their sociability seems to increase significantly.

Studies have indicated that vaccines containing thimerosal may contribute to the development of autism spectrum disorder. This concerning chemical was removed from children’s vaccines in 2001, but certainly could have been a cause of autism in young adults. To learn what vaccines still contain thimerosal, consult the list on this page, published by the FDA.

However, new studies show that while mercury may have been removed from vaccines, the risk remains. An increase in childhood vaccination is still linked to a spike in autism cases. However, vaccination frequency remains a difficult decision as many have hypothesized that viral infections can also contribute to autism’s emergence. The evidence on this theory is still unclear.

Furthermore, the vaccination records of the mother may have an effect. Infants whose mother had received an influenza vaccination in the first trimester had an increased risk of ASD. A more recent study showed that parents are suspicious of the MMR vaccine for similar reasons. 

Interestingly, lab studies do seem to correlate MMR vaccination with autism risk, but this is not supported when studied in the general population.

4. Maternal Factors

Health of the mother has emerged as another answer to the question of what causes autism. There are several factors that can affect development. Older parents are more likely to bear autistic children, and while the age of the mother is a primary factor, paternal age is also a concern. 

Interestingly, the odds of autism increase more for female children than for males based on maternal age.  

Furthermore, the odds of an autism diagnosis increase nearly 50% if the mother has been diagnosed with a mental health condition. Emotional disorder in mothers has also been linked to higher odds of autistic children. 

Another maternal factor that may increase autism risk is intake of vitamin D during pregnancy. The simplest way to get vitamin D is exposure to direct sunlight, and mothers who live in less sunny climates (or who are pregnant during the darker winter months) may have a harder time getting vitamin D. Because of this, it’s a great idea to supplement with vitamin D during conception and pregnancy as a preventative measure to avoid vitamin D deficiency.

Folate/folic acid intake may also influence autism risk. While folate is often thought of as the nutrient that serves to prevent neural tube defects, there is limited evidence that taking folic acid/folate during pregnancy may cut the risk of ASD in offspring by half.

During pregnancy, if a mother is infected by either rubella or cytomegalovirus and requires hospitalization, her risk for producing offspring with ASD is also increased.

5. Environmental Stress

Links are emerging between environmental stress and autism. While science has long thought that autism required additional stimulation and additional sensory experiences, the opposite may be true. 

One groundbreaking study showed that, in prenatal rats exposed to risk factors for developing autism, a predictable home environment dramatically lowered their chances of developing behavioral symptoms.

Early exposure to an unpredictable environment and too much exposure to screen time in the developmental years may cause autism. One recent report demonstrated that screen exposure early in life can compete with developing pathways in the social brain. 

This was confirmed in a 2018 study in which children exposed to screen time every day exhibited symptoms consistent with autism. Those with less than three hours of screen time showed minor symptoms, while kids who watched more than three hours of TV every day suffered from obvious impairment.

An unpredictable environment with too much screen time may overstimulate a child and push brain development toward autism. 

Comorbid Conditions with Autism

Autism has many comorbid conditions, or chronic issues that present alongside the disorder. Medical professionals have noticed that some behavior issues are due to discomfort or other underlying issues that have gone untreated. 

Additionally, these comorbid conditions can distract from a proper autism diagnosis. If one or more of these ailments is present, a deeper look is merited to ensure holistic treatment.

Digestive Issues

The symptoms of autism commonly include stress on the digestive tract. In one study on gastrointestinal symptoms in children with developmental disabilities, the link between digestive issues and autism was startling. 

Researchers found that 28% of children with no developmental disorder experienced digestive issues, while a massive 70% of those with autism experienced these symptoms. 

Autism research even indicates that children with autism may experience unique inflammation and gastrointestinal reactions. One study found a specific immunopathology in the digestive tract of autistic subjects that wasn’t present in other subjects with inflammatory bowel disease. 

In fact, though digestive problems are technically a comorbid condition to autism, it is postulated by many to also contribute to its development. Obviously, an inflamed digestive tract does not absorb optimal amounts of nutrients needed for childhood development. Not only that, but uncomfortable children experiencing the classic autism symptoms of diarrhea may be even more prone to acting out and behavioral issues, especially in those who are nonverbal.

The comorbidity of digestive issues and autism is an important factor to look for when diagnosing tummy trouble. If you or your child is experiencing this discomfort, I recommend microbiome rebalancing as a holistic step toward better digestive health. 

Proper supplementing, an anti-inflammatory diet, and allergy testing may help alleviate this issue, and therefore, some symptoms of autism. I’ll get into that in a future article.

Neurological Disorders

An important study in autism research found that inflammation of the nervous system and brain is more common in those with ASD. The study even found increased markers for tumor growth. 

This inflammation can potentially play a pathogenic, or disease-causing, role in the brain and nervous system. In fact, many aspects of the nervous system are well known to be affected by autism, and have an effect in return. 

Nervous system dysfunction can affect auditory processing as well. In one study, children exhibiting poor language abilities were seen to have trouble with their auditory nervous system. Researchers posited that this auditory issue may contribute to echolalia and language deficits that can occur in autistic individuals.

Additionally, researchers suspect that excess neuron numbers affect brain development and increase the risk of autism. The inflammation and neuron imbalance can certainly be an indicator of a deeper problem. If a patient is experiencing neurological issues, don’t rule out autism as a root cause or comorbid condition.

Frequent Infections

Children with autism are more likely than their peers to experience ear infections. Not only that, but there is an even greater correlation between lower functioning autistic children and chronic ear infections. Unfortunately, beyond being painful, these ear infections may also have an effect on hearing, speech, and social development. 

Some scientists hypothesize this is due to immune issues. The amount of prenatal and birth complications that occur in autistic children are higher than those in unaffected children. These immune system problems may contribute to the frequency of illnesses, like ear infections, in autistic children.

Sleep Disorders

Children with autism are much more likely to experience sleep issues. In one study, a startling 73% of autistic children studied suffered from a sleep problem. Another study estimated that up to 83% with this diagnosis having difficulty falling and staying asleep. This comorbid condition, like digestive issues, can also contribute to symptoms.

Any parent knows that tired children struggle more with mood swings and trouble focusing — two classic symptoms of autism. Sleep disorders may feed into these symptoms, as well as respiratory infections, poor appetite, and poor growth. Addressing sleep issues may assuage some other signs of autism as well.

Headaches and Migraines

Genetic disorders are still at play, even in comorbid conditions. Genes known to cause migraines are also being examined for playing a potential role in the development of autism. Also, these recurring migraines can compound with the general sleeplessness of autistic individuals. In some cases, these headaches may cause the sleep disorders previously mentioned. 

Obviously, beyond sleep disorders, headaches can contribute to behavioral issues as well. The lack of sleep migraines cause is a further stimulant for negative behaviors. Dealing with migraines may solve some behavioral issues and sleeplessness in autistic patients.

In Summary

  • No two cases of autism are the same, and the causes are individual, just like each person with ASD. Therefore, there is no simple answer to what causes autism.
  • Autism may be the result of genetic or environmental causes, and the rates of diagnosis are skyrocketing in the United States. Recent estimates show a rate of ASD in one of every 57 children, a massive increase from prior decades.
  • Genetic factors, environmental chemicals, certain drugs and vaccines, maternal factors, and environmental stress may all be legitimate causes.
  • Many conditions can present alongside autism, and dealing with them can help ensure a proper autism diagnosis. Addressing sleep issues, digestive problems, and more can explain and manage some behavioral symptoms.
  • Many of the comorbid conditions may compound and aggravate behaviors and symptoms associated with autism.
  • Furthermore, clearing up pain and discomfort may alleviate some of the behavior issues that can accompany autism.

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