Autism has traditionally been seen as a unitary condition with a wide spectrum of possible presentations.
This was not always the case.
In the past, there existed distinct types of autism, such as Asperger’s Syndrome. However, due to difficulties distinguishing between categories, Asperger’s Syndrome is now included under autism spectrum disorder (ASD).
Despite the wide range of presentations seen in individuals with ASD, it was assumed that all autism diagnoses exist on a spectrum and share similar underlying genetic profiles.
However, recent research is challenging this view. A 2025 study by Zhang and colleagues from Aarhus University has found distinct genetic profiles and developmental trajectories between those diagnosed with autism before the age of 6 (early childhood) and those diagnosed after (mid-childhood and beyond).
What Is Autism?
Before we delve into the study’s findings and their implications, let’s discuss autism in more detail.
According to Autism Resource Center (ARC) in Singapore, autism is a lifelong, brain-based neurodevelopmental condition. Neurodevelopmental conditions refer to conditions that affect the way our brains develop and grow. ARC estimates that 1% of the population in Singapore is on the autism spectrum.
Autism affects someone’s ability to think, feel, interact with others, and manage their surrounding environment.
The Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition, Text Revision (DSM-5-TR) is a manual that guides the diagnosis of neurodevelopmental and mental disorders internationally.
It outlined the following criteria for individuals to be diagnosed with autism:
1. Social communication (all must be met)
- Difficulties with social-emotional reciprocity, e.g. awkward or unusual approaches and initiations with people, difficulties initiating, reciprocating, and maintaining conversations with others
- Nonverbal communication, e.g. difficulties maintaining appropriate eye contact
- Developing and maintaining relationships
2. Restricted, repetitive behaviours, interests or activities (any two or more of the following)
- Stereotyped or repetitive motor movements, speech, or use of objects, e.g, echolalia, flapping hands, rocking movements, or lining up objects that aren’t usually lined up
- Insistence on sameness or inflexibility in routines and behaviours, e.g., difficulties regulating emotions when plans or routines change
highly restricted and fixated interests, e.g. strong and unusual interest in wheels or round objects, being able to ride in buses or trains for a long period of time - Hyper- or hyposensitivity to sensory stimuli or unusual interest in sensory aspects of the environment, e.g. smelling toys, putting objects in their mouths
Autism, as it is currently defined and diagnosed, is a spectrum with core difficulties in social communication and interaction skills. Clinicians look for patterns of difficulties across multiple settings (school, home) and time.
It is crucial to note that identifying with a few traits in the diagnostic criteria does not automatically mean that someone has autism or is on the spectrum. Most of us exhibit these traits at times.
For example, some people have heightened sensitivity to sound or dislike disruptions to their schedules. However, this does not mean that these traits are autistic.
What’s The Big Deal With The Study?
Now that we understand how autism is currently defined and diagnosed, we can put the study into perspective and appreciate its significance.
Previously, we assumed that those diagnosed later had “milder” forms of the same condition, or that the symptoms only became clearer as children grew older. The field also thought that other factors affected the age of diagnosis, such as gender, stigma and access to healthcare.
What The Study Found
1. Underlying genetic differences between those diagnosed in early childhood and those diagnosed later:
- Autism diagnosed in late childhood may be genetically different from autism diagnosed in early childhood.
2. Those diagnosed early tended to:
- Display difficulties with social communication, motor, and behavioural difficulties
3. Those diagnosed later tended to:
- Have increased social and behavioural challenges in adolescence
- Genetically predisposed to have a higher risk of mental health difficulties such as depression and post-traumatic stress disorder (PTSD)
- Higher genetic overlap with attention deficit hyperactivity disorder (ADHD), suggesting that the underlying genetic profiles are more similar to ADHD
So What Does This Mean?
The study challenges our current view that autism is one underlying condition, and suggests that there may, in fact, be different types of autism than initially thought.
Autism is currently defined as a neurodevelopmental condition that typically starts in childhood. However, research also shows that there are more people who are being diagnosed later.
Rather than assume this phenomenon is unclear symptom presentation, gender, or access to healthcare, this study suggests that there are underlying genetic differences. This could lead to more research into defining other autistic categories and refining interventions for individuals of different subtypes of autism
Further research could also shed some light on gender differences in diagnosis. Girls are more likely to be diagnosed later than boys. It was assumed that our current knowledge of autistic traits was largely based on presentations seen in boys and, as such, harder to pick up in girls.
Girls were also known to ‘mask’ their traits better by suppressing certain behaviours to fit into societal norms, whether consciously or unconsciously. However, this research opens up the conversation for the possibility that it may be different types of autism altogether.
Final Thoughts
It is exciting to see more and more research into autism that sheds more light on this complex disorder. As someone who has worked with children on the spectrum, I know firsthand that each autistic individual is unique, with their own unique gifts and strengths.
It is so important for us to recognise and celebrate those strengths while also supporting them in whatever challenges they may face. As our understanding deepens, research like this reminds us that autism is as diverse as the people who experience it.
Written by Bibiana, Clinical Psychologist at Us Therapy