HHS Secretary Robert F. Kennedy Jr has declared that there is an epidemic of autism and that there must be some environmental toxin that is causing it. The evidence says otherwise. I will review the evidence in this post.

Increased diagnosis of autism

There is no question that autism is being diagnosed more frequently than in the past. According to the CDC, in 2000 the prevalence of autism was 7 per thousand 8 year old’s and by 2024 was 32 per thousand, a 4.5 times increase.

Evolution of diagnostic criteria for autism

Up until 1980, autism was considered a form of schizophrenia in children. It was thought to be rare, probably because many of these children were institutionalized. Over the various versions of the DSM (Diagnostic and Statistical Manual) criteria over the years, the criteria to diagnose autism have been constantly expanded, resulting in a progressive increase in the frequency of the diagnosis of autism. In the most recent version of the DSM all the subcategories of autism including Asperger’s disease were combined into one diagnosis – autism spectrum disorder. This resulted in a marked increase in the diagnosis of autism, because it included all the less severe forms of autism. There is an excellent description of this evolution on the Arizona Autism United blog: How the Autism Diagnosis Has Evolved Over Time.

Has the frequency of severe autism increased?

Severe or profound autism includes children who have no or little speech, are intellectually disabled, and some have challenging behavior that interferes with safety and well being. According to the CDC, people with severe autism make up about 26% of people with autism. Kennedy says that severe autism has markedly increased. According to Christine Ladd-Acosta, who is the vice director of the Wendy Klag Center for Autism and Developmental Disabilities, the data show that severe or profound autism has increased little or none in the last 10 years. Maureen Durkin, another well known autism researcher, divided autism cases up into different buckets. She found that severe autism has not increased at all, and in fact has decreased a little.

Screening for autism spectrum disorder

The American Academy of Pediatrics began recommending screening children for autism spectrum disorder in 2006. Screening is recommended at well child visits. There is some controversy about the benefits of screening children with no symptoms, but it is clear that screening has increased the diagnosis of autism spectrum disorder, especially milder forms of autism. Screening has also resulted in earlier diagnosis of children with more severe autism. Earlier intervention improves the outcomes in these children.

Causes of Autism Spectrum Disorder

Genetic Causes

Multiple studies including identical twin studies have shown the cause of 80% of autism spectrum disorder cases are genetic. Here is a link to an NIH article that summarizes these studies. Genetic causes are both hereditary and caused by genetic mutations.

Environmental causes

There are certain environmental factors associated with slightly increased risk of autism spectrum disorder. All of these factors account for a very small increase in the incidence of autism spectrum disorder, each less than 1%.

• Advanced parental age
• Prenatal exposure to air pollution or certain pesticides
• Maternal obesity, diabetes or immune system disorders
• Extreme prematurity or very low birth weight
• Birth complications leading to periods of oxygen deprivation to the baby’s brain

Do childhood vaccines cause autism spectrum disorder?

The answer to this is a definite no. Multiple large well designed studies have shown no association of vaccines, or any component of vaccines including thimersal and aluminum that have any association with autism spectrum disorder. Here is a link to an article from the CDC summarizing these studies.

Does taking Tylenol (acetaminophen) during pregnancy cause autism?

Once again the answer is no. There were a few small studies that showed an association of acetaminophen during pregnancy and development of autism spectrum disorder. Larger, better designed studies have shown no association of acetaminophen use during pregnancy and subsequent development of autism spectrum disorder in children born from those pregnancies.

Autism spectrum as neurodiversity

Many people with milder forms of autism spectrum are fully functional and live independently. They view themselves as on a spectrum of neurodiversity rather than having a disorder. Here is a link to an article from Autism Speaks describing the idea of neurodiversity.

Bottom Line

The increase in the incidence of autism spectrum disorder is almost entirely due to increased diagnosis and increased awareness. The cause of 80% of autism spectrum disorder is genetic. There are a few environmental causes that have increased over time, but these account for only a tiny portion of the increase. There are many well designed studies that show that vaccines do not cause autism spectrum disorder. There are also similar large well designed studies that show that taking acetaminophen during pregnancy does not cause autism spectrum disorder in the babies born from those pregnancies.

Many people on the autism spectrum are fully functional and live independently. They view themselves as people with neurodiversity rather than people with a medical disorder.

There is a very good podcast called Science Versus that reviews all of the evidence that I have outlined above. It is worth listening to. Here is a link to the transcript of the podcast. You can listen to the episode on your normal podcast app. The show notes for the episode has all the references that are used in the episode.