Doctors diagnose autism based on a child’s or adult’s behaviour. Photo / Getty Images
Autism cases are increasing globally, but its causes are difficult to specify.
US Health and Human Services Secretary Robert F. Kennedy jnr has vowed to discover the cause of autism by September, saying the “autism epidemic is running rampant”. While cases are on the rise – often because of better screening and greater awareness – the actual causes aren’t easy to pinpoint. It’s a complex condition, and symptoms may vary from person to person.
Here’s what experts and decades of scientific research have to say about autism.
“Autism is not one condition,” said Geraldine Dawson, professor of psychiatry and behavioural sciences at Duke University and founding director of the Duke Centre for Autism and Brain Development. “It is many different conditions with many different causes.”
Autism, more formally called autism spectrum disorder, is a neurodevelopmental condition characterised by difficulties in social and communication skills, and repetitive behaviours.
Symptoms are varied and include:
An autism diagnosis encompasses a wide spectrum of challenges and strengths, reflected in a saying in the autism community: “If you’ve met one person with autism, you’ve met one person with autism.”
On one end, about 30% of people with autism have substantial intellectual disability, very limited language skills and might need a lifetime of care.
On the other end, “often we don’t necessarily think about the strengths and the unique talents and … the importance of having neurodiversity contributing to our society,” Dawson said.
Intense focus on particular interests might help produce savant skills in math, computer science, music and arts; research shows special abilities are more common in autistic people.
Differences in how autistic individuals socialise might not always be a bad thing, researchers said.
“There’s something very sincere and authentic about being able to see and say things that are unencumbered by social conventions,” said Bryan King, vice chair for child and adolescent psychiatry at the University of California at San Francisco.
Given that autism is many different conditions, there’s likely not a single cause. But changes in the brain, particularly in areas responsible for social interaction and communication, is the common factor, researchers said.
These brain changes are thought to begin before birth, experts said.
Neuroimaging studies have found alterations to brain regions and circuitry as early as six months of age in children who would later be diagnosed with autism. These infants had accelerated brain growth of the cortex compared with siblings who were not diagnosed with autism. Other research shows indications of altered brain functioning that can be picked up at 3 and 6 months of age.
The consensus after 30 years of research is that “if you are autistic, you were born with it,” said David Amaral, a professor of psychiatry and behavioural sciences at the University of California at Davis and editor in chief of the scientific journal Autism Research.
Genetics plays a large role. Autism is also 80% to 90% heritable, research shows.
Environmental factors can also influence prenatal brain development.
When someone is pregnant, chronic inflammation, such as in response to a serious infection or because of health conditions such as obesity and diabetes, could affect fetal brain development and autism risk, and is an area of active research around what is known as the maternal immune activation hypothesis.
Researchers have looked at pesticides, air pollution and water pollution and have found increases in risk that have “a small effect size” and are correlational, but not necessarily causative, said Charles Nelson, a professor of paediatrics and neuroscience at Boston Children’s Hospital and Harvard Medical School.
Vaccines do not cause autism, research has repeatedly shown. The measles, mumps and rubella (MMR) vaccine has often been blamed, but Amaral noted its first dose is given at 12 to 15 months of age, which is after the brain changes associated with autism are observed.
“It’s a deeply complex gene-environment interaction where genes interact with other genes and multiple factors in the environment interact with each other,” Nelson said.
Doctors diagnose autism based on a child’s or adult’s behaviour.
“There’s not yet a blood test or a biochemical test or a biometric test, although there may be in the future,” said Fred Volkmar, professor emeritus of child psychiatry, paediatrics and psychology at the Yale University Child Study Centre.
The American Academy of Paediatrics recommends that all children be screened for autism at 18 and 24 months of age, with their regular developmental monitoring. The average age of actual diagnosis in the United States is about 4 years.
Proper diagnosis often requires help from different medical specialties. Paediatricians use standardised screening tools, such as the Modified Checklist for Autism in Toddlers (M-CHAT-R), and refer children at risk for autism to specialists for comprehensive follow-up evaluation.
Autism can be reliably diagnosed in children by 18 to 24 months of age, but differences in behaviour can be detected earlier.
Around ages 6 to 9 months, infants later diagnosed with autism typically pay less attention to faces, make less eye contact, engage in less social interaction and babble less, Dawson said.
By age 1, the infants may not turn when their name is called, or by 18 months, there may be language delays.
“What I like to tell parents is that they shouldn’t worry about this, but they should be vigilant” just like with their child’s other developmental milestones, Nelson said.
Autism can also be diagnosed in adulthood by a psychiatrist, psychologist or neuropsychologist.
A number of factors are known to increase the chance a child will develop autism, such as:
Autism cases are increasing globally, according to a large 2022 meta-analysis which reported that approximately 1 in 100 children are diagnosed with autism worldwide. Boys are four times more commonly diagnosed than girls.
A recent report from the Centers for Disease Control and Prevention estimated that autism prevalence in the United States is about 1 in 31 children using 2022 data, an increase from 1 in 150 children in 2000.
However, experts stress autism is not an epidemic.
At least some of this increase in cases is probably because of better screening, more awareness and a broader diagnostic criteria for autism, researchers said.
Autism screening is standard at paediatricians’ offices, which was not the case decades ago, meaning more cases are diagnosed, Nelson said.
The diagnostic criteria of autism have also broadened to include milder, more subtle symptoms.
A large 2015 study of all children born in Denmark from 1980 to 1991 found that 60% of the increase in autism prevalence was because of a broadening of the diagnostic criteria and changes in reporting practices.
In addition, there are health and school services directly linked to an autism diagnosis, King said. “So there’s an incentive not to miss it,” he said.
For instance, California had more than five times the prevalence of autism than Texas in the recent CDC report, but California also had an education campaign for autism awareness as well as state benefits to support autism services.
There may also be other factors contributing to a real increase in autism prevalence, though it is difficult to know how much. For instance, there are more older parents; more preterm babies are surviving; and autoimmune diseases are on the rise, which are all risk factors for autism.
“It’s very hard to actually track the real rise in autism prevalence because so many factors are changing over time,” Dawson said.
Individualised, and particularly early, behavioural interventions have been shown to improve social skills and functioning by shaping social behaviour and reducing symptoms.
One frequently used behavioural therapy, applied behaviour analysis, encourages positive behaviours with rewards while discouraging undesired behaviours.
The Early Start Denver Model is a “play-based intervention that helps draw the child’s attention to other people” and helps them learn skills such as eye contact, gesture and language, said Dawson, who helped develop the program.
About 10% of children with autism lose their diagnosis as they get older, and girls tend to improve more than boys. A 2023 paper reported that 37% of 213 participants no longer met diagnostic criteria for autism by age 7.
There aren’t any medications specifically for autism.
Doctors may prescribe antipsychotics to manage children who have outbursts and tantrums. They may also give other medications for any additional condition such as attention-deficit/hyperactivity disorder, anxiety or seizures.
“Many people and scientists are working really hard to try and understand what causes autism and how could autistic individuals benefit from individualised personalised treatment, not to necessarily change their autism, but to help them with some of the disabling features that co-occur with autism,” Amaral said.
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