Autism: widely known, rarely understood

AUTISM spectrum disorder (ASD), commonly known as autism, maintains a unique position in public imagination: it is a condition that is widely known but rarely understood.

Significant research advances have greatly increased what we know about autism, and how we can best support children and adults across their life.

What is autism?

Autism is a diagnosis that describes people who, in varying degrees, have difficulties with social interaction and communication, and who display restricted and repetitive behaviours. The latter encompasses “stereotyped and repetitive motor movements” such as the flapping of hands or lining up toys, fixated or unusual intensity in certain interests, and unusual sensory responses to the environment (eg, apparent indifference to pain or temperature, and excessive smelling or touching of certain objects).

The intensity of the behaviours that characterise autism vary considerably between individuals. Communication skills can range from having no verbal language to fluent language, the frequency and intensity of repetitive behaviours vary between mild and severe, and intellectual disabilities can range from severe disability to very high IQ. The variation in the severity of autistic behaviours is what is often referred to as the “autism spectrum”.

Autism is not just a childhood condition. Whereas the behavioural characteristics of autism tend to emerge in the first 3 years of a child’s life, they almost always persist into adolescence and adulthood, but often present in a different form. For example, social difficulties in childhood might be shown through a preference to play alone, while in adulthood this may be reflected by difficulty in maintaining social relationships. Similarly, a restricted and repetitive interest in childhood may be an unusually intense focus on a certain toy, while in adulthood this may manifest though extraordinary knowledge of sport statistics.

In Australia, we have a national guideline that describes a best practice approach for assessing and diagnosing autism. This can be freely downloaded by clinicians who register with the website.

What might cause autism?

Over the past two decades, we have learnt a great deal about why some children develop autism. Autism is not one condition in the sense that there is a common cause shared by all individuals on the autism spectrum. Instead, autism is best thought of as an “umbrella term”, which describes a range of different children, all with relatively similar behaviours, which may or may not be caused by the same biological factors.

Twin studies have shown very clearly that genetics play a large role in autism. In a minority of cases, there may be very clear genetic variants that have led the brain to develop differently, such as such as in fragile X syndrome (FMR1 gene), Rett syndrome (MECP2 gene), and tuberous sclerosis (TSC1 or TSC2 gene). However, a likely prospect is that the majority of cases of autism will be caused by what is called “common genetic variation”. This refers to differences in genes that are also found in many individuals who do not have autism and by themselves are not sufficient to cause the autism. However, when several of these genetic variants occur in the same person, they combine to have a major effect on how the brain develops. There are many combinations of genetic variants that may result in the brain developing differently, and understanding this remains a major research focus.

Is autism more common now than before?

When I started in the field in the late 1990s, autism was diagnosed in about one in every 2500 children. However, this rate increased substantially throughout the 2000s, to the point where most recent estimates indicate a diagnosis rate of around one in every 50 children. Current evidence suggests this rise in prevalence might be related in part to clinical diagnostic reasons, such as changes in diagnostic criteria.

The diagnostic criteria for autism, outlined by the Diagnostic and Statistical Manual of Mental Disorders (or DSM), has changed over time. In the 1980s, the diagnostic criteria outlined by the third edition of the manual (DSM-III) specified a very narrow definition for autism, in which children had to have significant intellectual disability to receive a diagnosis of what was termed infantile autism. However, the behaviours used to define autism were broadened out in subsequent editions of the DSM (including the current version, DSM-5), where it was recognised that individuals may have autistic behaviours without having intellectual disability. This change in the definition of autism spectrum disorders contributed to the increasing number of children who met criteria for autism during the 1990s and 2000s.

The increased awareness of autism in our community also has the effect of changing diagnostic decision making among clinicians, where children who would in earlier generations have received another diagnosis are now identified as having autism. This is particularly true for the diagnoses of intellectual disability or language disorders, which have been diagnosed at decreasing rates across the same period (here and here), such that we have seen an increase in the numbers of individuals diagnosed with autism.

Are autism characteristics different between males and females?

ASD is diagnosed more commonly in males than females, with a male-to-female ratio of 4:1. However, there is recent evidence that this may not reflect the true sex ratio of ASD but may represent a bias towards males in the diagnostic process.

Recent research has found that boys are more likely to be identified with autism than girls, even when symptoms are equally significant. There is also evidence that females are better able than males to mask their symptoms (here and here) by using compensatory strategies, particularly when no intellectual disability is present. The national guideline provides guidance on how autism may present in females with average or high IQ (Table 1).

Table 1. Characteristics that may be more common in females with ASD who have an average or high IQ compared to males with ASD with average or high IQ

How do we support individuals on the autism spectrum?

The delivery of therapy to children on the autism spectrum provides an important opportunity to support development, minimise disability, and maximise each child’s strengths and opportunities over the long term. Therapies are typically non-pharmacological and are designed to advance developmental skills across a range of areas, such as social communication, language, cognition, and adaptive functioning.

In 2020, I was part of a team that reviewed the evidence for the effectiveness of autism therapies. In this report, which is able to be freely downloaded, we found that there is no one-size-fits-all approach to clinical support during childhood and that therapies need to be matched to a child and family based on a combination of empirical evidence, clinical judgement and individual context.

Although therapies are often focused on the childhood years, individuals on the autism spectrum often have life-long support needs. Ongoing clinical management to support education and independence, and to promote physical and mental wellbeing, is of critical importance to fostering quality of life across the lifespan.

What is neurodiversity?

Since its first formal description in 1943, our understanding of autism has evolved along with broader community attitudes. At one time, autism was viewed solely through a medical model lens, in which autism was a disorder of impairments and was to be treated. Over the past two decades an alternative view of autism has gained momentum, called neurodiversity.

Neurodiversity challenges the medical model of autism as a disorder, instead viewing autism as part of the natural variation in development and behavioural functioning. The movement points to other aspects of humanity such as ethnicity or sexual orientation, variations of which have been pathologised as disorders in the past, but which are now seen as part of normal human differences. In this regard, neurodiversity advocates a call for intervention services to improve quality of life and wellbeing, while also respecting and preserving autistic ways of being.

We now know a great deal about how best to support autistic children and adults. GPs will most often become the so-called medical home for autistic children as they enter adulthood and age out of paediatric services. Our ultimate goal is to help children and adults discover, define and achieve what they want in their own lives. Establishing relationships with the broader allied health support team is critical to delivering holistic clinical management to reach that aim, and to understand when additional support or further referral may be necessary.

Professor Andrew Whitehouse is the Angela Wright Bennett Professor of Autism Research at Telethon Kids Institute and the University of Western Australia.

The statements or opinions expressed in this article reflect the views of the authors and do not represent the official policy of the AMA, the MJA or InSight+ unless so stated.