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Research on the causes of autism is still in its infancy but substantial progress has been made in recent decades on understanding the condition, writes Professor David G. Amaral, founding Research Director of the MIND Institute.
Autism was first described by the American psychiatrist Leo Kanner in 1943, but it was not formally designated as a psychiatric condition until 1980.
So, in a very real sense, research on the causes and courses of autism is still in its infancy. Nonetheless, substantial progress has been made by the global autism research community.
Autism, characterised by social challenges and repetitive behaviours, is a heterogeneous disorder that has many causes and different trajectories throughout life in different individuals.
It is also associated with several co-occurring conditions such as intellectual disability, epilepsy, anxiety, ADHD, sleep disorders and gastrointestinal problems. Much has been clarified about the etiology and phenomenology of autism, though many questions remain.
The clinical knowledge
It is quite clear that whatever the causes of autism, the effect is on foetal brain development during pregnancy. In other words, if you are autistic you were born with autism.
We now know from magnetic resonance imaging studies that the brains of children who will receive a diagnosis of autism are already altered by six months of age, even though the behavioural signs of autism appear much later.
The largest contribution to the causes of autism is a person’s genes. There are an increasingly large number of genes – approaching 200 – that research has demonstrated can increase the likelihood of an autism diagnosis if they are dysfunctional.
These so-called rare variant genetic changes are currently believed to account for up to 20% of autism. Beyond this, autism geneticists believe that more subtle configurations in the genome of an individual contributes to as much as 60% of the causes of autism, though the exact details of how this happens has not yet been worked out.
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Other factors that may contribute to the causes of autism include maternal infection or maternal immune activation during pregnancy, as well as environmental contaminants such as air pollution.
The best examples of a nongenetic cause of autism are maternal rubella infection during pregnancy and drugs like valproic acid, which is an approved treatment for epilepsy.
To summarise, the major causes of autism, accounting for perhaps 80% of all cases, is genetic. While there may be some environmental contributions, the evidence supporting this is still being gathered.
Changes throughout life
So, what are some of the other changes in our appreciation of autism that have come from research? One is that autism severity can change throughout life. While 30 years ago it was believed that if you were born with autism, you would be autistic for the remainder of life that turns out not to be true.
A sizable minority – up to 10% or so – of autistic individuals diagnosed early in life actually lose their diagnosis in middle childhood or beyond. Even if the diagnosis does not disappear, the severity of a person’s autism can diminish substantially, due in part to behavioural intervention, as one gets older.
Girls are more likely to decrease their autism severity than boys. This also highlights a major area of current research indicating that both the biology and behaviour of autistic girls can be strikingly different from autistic boys.
While much progress has been made, there are still some daunting questions that research must resolve including:
- Why do some autistic individuals have a profound form which is accompanied by intellectual disability whereas others have amazing intellectual abilities?
- Why are more boys diagnosed with autism than girls?
- What biomarkers are useful in diagnosing the likelihood of autism even before behavioural signs emerge?
- What are the precise brain alterations that are associated with autism and can they be modified?
There is substantial optimism that, with consistent support from governments and families, these and other questions can and will be answered.
Professor Amaral also works out of the University of California and launched the Autism Phenome Project, the largest single-site study of autistic children.
Join Autism WA at the Asia Pacific Autism Conference 2025, hosted by the Autism Association of Western Australia, to hear from Professor Amaral and other leading national and international experts in the field of autism.
Register today Registration | APAC – Asia Pacific Autism Conference
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