What Causes Autism Spectrum Disorder and Why Are More and More Kids Being Diagnosed with It?

Nina Zeldes, PhD

Does a friend or family member have a child with autism spectrum disorder (ASD)? ASD rates seem to be skyrocketing. Among children who are 8 years old, ASD diagnoses have more than tripled from 1 in 150 (for children born in 1992) to 1 in 44 for children born in 2010. [1] This increase is partly due to changes in the diagnosis of autism, which has been included under the umbrella of Autism Spectrum Disorder starting in 2013. This article discusses what we know about the causes of this disorder and why more and more children are diagnosed with ASD.

What is Autism Spectrum Disorder?

Autism spectrum disorder (ASD) usually involves delayed verbal communication and difficulties in social interactions. It is considered a developmental disorder because symptoms usually appear in the first two years of life and it can be diagnosed at any age. Early diagnosis can help families understand the symptoms of ASD and find help to manage those symptoms and reduce the problems they can cause. [2, 3]

Boys are more than four times as likely to be diagnosed compared to girls. However, more research is needed to determine if girls are indeed less often affected, or if they are only less frequently diagnosed with ASD. Some research indicates that the kinds of ASD symptoms girls show are different from the “typical” symptoms described for boys and thus not recognized or diagnosed much later than in boys. Girls may also be better at camouflaging their symptoms or compensating for them. While more research is needed to determine if the diagnosis and treatment of ASD needs to become more gender specific, a 2022 study has demonstrated that there are differences in how the brains of boys and girls with ASD are functionally organized, which may explain the differences in the symptoms affected boys and girls show. [4]

In 2013 the American Psychiatric Association combined 4 conditions that used to have separate diagnoses into an umbrella diagnosis of “Autistic Spectrum Disorder”. [5,6,7] This term covers the following conditions, which vary in their severity:

  • Asperger Syndrome, which is usually milder symptoms that affect a person’s social interactions
  • Autistic disorder, previously known as “classic autism”
  • Childhood disintegrative disorder, diagnosed in children who first appear to develop typically and then lose skills associated with movement, language, or coordination
  • Pervasive developmental disorder not otherwise specified (PDD-NOS) also known as “atypical autism”. It includes some, but not all features of autistic disorder or Asperger syndrome

What Causes Autism Spectrum Disorder?

The exact cause or causes of ASD are still unclear. However, experts believe that there are probably many factors involved.

Most experts agree that a genetic cause is one of the most important. For example, siblings of a child with ASD are much more likely to be diagnosed with ASD.[2] There are probably hundreds of genes that could influence whether a child is at risk or not. Researchers are also looking at different biological and environmental factors that may contribute to a child developing ASD. Most research indicates that these factors alone do not cause ASD, but they could play a role in children that already have genetically higher risks for developing ASD.[8, 9] These include:

  • Having a father over the age of 40
  • Premature births, extremely low birth weight, hormonal induction, and several assisted reproductive technologies
  • Certain antiepileptic drugs taken during pregnancy, including valproate, oxcarbazepine, and lamotrigine
  • Some antidepressant drugs taken during pregnancy and some psychiatric disorders of the mother
  • Particularly for boys the painkiller acetaminophen (Tylenol) taken during pregnancy
  • Longer screen time for boys in their first year of life [2, 9, 10, 11, 12, 13]

Studies have also examined whether exposure to different kinds of prescription drugs, pesticides, phthalates, air pollution and other toxins could increase a child’s risk to develop symptoms. However, more research is needed as studies have either not been confirmed or found conflicting results. For example, while some studies from the US, Canada, Taiwan, and Israel show that air pollution may be a risk factor, studies conducted in Europe did not find any association. [10, 13, 14]

 No statistically significant links between ASD and vaccinations have been found, despite reports regarding individual children. [3, 14]

Autism Spectrum Disorder and Other Conditions

There are some conditions that seem to occur more frequently in children diagnosed with ASD. For example, studies have shown that epilepsy and seizures are also common for people with ASD. Researchers think that underlying genetic or environmental factors make it more likely for ASD patients to also suffer from epilepsy or seizures and for epilepsy patients to be more likely to also be diagnosed with ASD, but we do not yet know how these two conditions are related. [10,15] Other research has also shown that boys with genital birth defects, such as an abnormal position of the urethral opening (hypospadias) or undescended testicle(s) (cryptorchidism) are more likely to be diagnosed with ASD. And like autism, genital malformations are increasing. For example, between 1980 and 2010, 1.6 times more boys were diagnosed with hypospadias. [16] However, both of these birth defects are relatively common, some are associated with a mother’s exposure to hormone-disrupting chemicals, and how they relate to ADS has not yet been fully understood. In fact, several studies did not conclude that these birth defects make it more likely for boys to also be diagnosed with ASD. Although more research is needed to confirm if and how these two conditions are related, children who are born with these birth defects should be monitored for early signs of ASD to allow for early treatments and interventions. [17, 18, 19]

Why Are More Kids Diagnosed with Autism Spectrum Disorder?

Although the number of children diagnosed with ASD has more than tripled since the early 1990s, it is not known if changes in environmental exposures are the key reason for the increase. There are other reasons that would explain the higher number of diagnoses. [5, 6, 7]

  1. Policy changes and the broadening of the definition by adopting the umbrella term ASD have helped to identify more children, especially those with less severe symptoms. Starting in 2006, children between 18 and 24 months were also screened for symptoms at their routine pediatrician visits, which helped identify more children, again especially those with milder symptoms.
  2. Before the new terminology was introduced in 2013, physicians had to choose one disorder when diagnosing a child, even if the patient showed signs of several conditions. Today, physicians can diagnose a patient with more than one condition, for example a patient can be diagnosed with ASD as well as Attention-Deficit/Hyperactivity Disorder (ADHD).  This change might have also led to more children receiving an ASD diagnosis overall.
  3. The increase in screening and better diagnosis options have consequently also led to more awareness for this condition. And it is now much more likely that parents will consult with pediatricians if they are concerned about their child’s development.

Nevertheless, several of the biological and environmental factors associated with ASD and discussed above have also become more common in recent years. In addition to exposure to more hormone disrupting chemicals, these include a rise in older parents and parents using assisted reproductive technologies. Medical advances have also given very premature babies better chances of surviving, all of which could lead to more children being at risk for ASD.

Keep in mind that the way in which the data on ASD are collected is not perfect. For example, White boys from urban areas who have health insurance are most likely to be diagnosed with this condition. [5, 20] In some states (such as California) many more children are diagnosed with ASD than in others (such as Missouri). [1] Researchers think these differences in numbers are due to, for example, different levels of awareness, requirements for diagnosis and the number of services offered for affected families. For example, states that require a physician or psychologist to diagnose autism for families to qualify for special education benefits tend to have lower overall rates of ASD. [5, 21]

Diagnosis and Treatment Options for Autism Spectrum Disorder: What We Do Know

Children with ASD should be diagnosed as early as possible, preferably in the first two years of life. A diagnosis early in life allows behavioral therapy or other treatments to begin when they seem to be most effective to strengthen patients’ skills and can help reduce some of the symptoms associated with ASD. However, most patients benefit from treatment regardless of their and age. [2, 22, 23] Early diagnosis signs of autism may include symptoms such as:

  • Little eye contact or avoidance of eye contact
  • No response to the child’s name by 9 months
  • No or few facial expressions to show happiness, sadness, or surprise by 9 months
  • Child uses few or no gestures such as waving hello by age 12 months
  • Rocking of body, flapping hands, or spinning in circles
  • Delayed language or movement skills
  • Excessive lining up of toys or objects
  • Rigid importance of following routines

A final diagnosis and individualized treatment plan should be made by a team of qualified professionals including a developmental pediatrician, neuropsychologist, psychologist, psychiatrist, and speech pathologist. The outlook for children with autism is improving as we learn more, and many children can improve significantly within a few years of treatment.

While there is no cure for this disorder, there are several educational, psychological and behavioral therapies, medications and other interventions that may substantially improve the child’s symptoms. Since every patient is different, the ideal treatment plan needs to address the specific needs of the child.

Medication can be prescribed to help manage some common symptoms associated with ASD, if other strategies are ineffective [24, 25]. However only 2 drugs are FDA approved specifically for children with ASD. These two drugs, Risperidone and Aripiprazole, are considered “atypical antipsychotic medications” that can also be prescribed to reduce irritability for children. They also have several serious side effects, such as increasing one’s appetite and leading to substantial weight gain, if the calorie intake is not closely monitored by caregivers. This weight gain can then put patients at a higher risk of developing insulin resistance and metabolic syndrome, which in turn can lead to higher rates of diabetes and heart disease. Other relatively common side effects of these drugs include tremors and tics (dyskinesia) and drooling, which can be permanent. Risperidone has also been shown to temporarily increase the production of the hormone prolactin with can lead to enlarged breast tissue, in boys and girls. [25, 26, 27].

For other common symptoms of ASD, such as self-harming behavior; depression; difficulty concentrating; or seizures, there are no medications specifically for children with ASD. Instead, health care providers prescribe drugs to ASD patients “off label” – meaning these drugs are FDA approved for other conditions, but not specifically for the treatment of children with ASD. [24, 25] These include:

  • antidepressants (selective serotonin re-uptake inhibitors or SSRIs) that are meant for the treatment of anxiety disorders and depression, are sometimes prescribed off label to treat depression in children with ASD
  • naltrexone, which is a drug that is FDA approved to treat substance addiction, is sometimes prescribed off label to children with ASD to treat repetitive or self-injuring behaviors
  • simulants that are used to treat Attention Deficit Hyperactivity Disorder (ADHD), are sometimes prescribed off label to ASD children who have difficulty concentrating
  • Anticonvulsants that are approved to treat epilepsy and other seizure disorders are sometimes prescribed off label to treat seizures in ASD patients

Prescribing these drugs “off label” is legal, but that does not mean it is a good idea.  FDA approves drugs for specific health problems and for specific types of patients, based on studies indicating that the benefits outweigh the risks.  When a drug is prescribed off label, that means the FDA has not determined whether the benefits outweigh the risks for that type of health issue or that type of patient.  All these drugs can have serious side effects and patients with ASD sometimes react differently to these drugs than other types of patients. Parents should therefore ask the child’s health care professional if there are studies indicating that the benefits of these drugs outweigh the potential side effects for children with ASD.

Parents should also be aware that the FDA has released warnings about unproven treatments for ASD. For example, “Chelation Therapies” are detoxifying products that are approved for the treatment of lead poisoning. When used inappropriately, these products can be harmful or even life-threatening.  Another example is breathing oxygen in a pressurized chamber, called “Hyperbaric Oxygen Therapy”, which is not a treatment or a cure for ASD.  Although this is cleared by the FDA to treat decompression sickness in divers, it is not proven to be safe or effective for ASD. The FDA also warns about the use of dietary supplements that falsely claim to help cure or treat autism, including Miracle Mineral Supplement or MMS (chlorine dioxide), detoxifying clay baths, raw camel milk, and essential oils. [28]

Bottom Line

Rates of children with Autistic Spectrum Disorder have dramatically increased in recent years. While the exact reasons are not yet clear, changes in how the disorder is defined, increases in screening, and more awareness certainly contribute to this increase.

If you have any concerns about your child’s development, speak to a healthcare professional about diagnostic tests.  If your child is diagnosed, ask a healthcare professional about treatment options and available services. Do not start any intervention or treatment that claims to cure ASD, because there is no cure for this condition. However, appropriate therapies started early in a child’s life can help people with autism spectrum disease to reduce or manage their symptoms and build their skills.

All articles are reviewed and approved by Dr. Diana Zuckerman and other senior staff.

The National Center for Health Research is a nonprofit, nonpartisan research, education and advocacy organization that analyzes and explains the latest medical research and speaks out on policies and programs. We do not accept funding from pharmaceutical companies or medical device manufacturers. Find out how you can support us here.


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