The phrase “on the spectrum” has become widely associated with autism, yet it frequently masks a fundamental misunderstanding. This notion suggests a linear progression of autistic experiences and behaviours, differing only in degree. The reality, however, is far more nuanced and varied.
Autistic individuals present a broad range of characteristics. Some may be non-verbal, while others exhibit hyperfluency and a highly articulate communication style. Sensory sensitivities also differ; some are acutely attuned to loud noises and bright lights, while others react oppositely. Similarly, while some display rigid routines and engaging in repetitive movements like hand-flapping, others demonstrate adaptability but dedicate significant time to intense “special interests,” which can span subjects from Tudor history to complex puzzles.
This profound diversity within autism is a cause for celebration. Nevertheless, it has historically posed a considerable challenge to researchers attempting to map this intricate array of traits. Recent advancements, however, are beginning to offer clearer insights. Several studies have identified distinct subgroups within the overarching category of autism, each underpinned by specific genetic patterns and brain activity signatures.
Current research endeavors explore the potential of these subtypes to inform more effective, personalized support for autistic individuals and to foster a deeper self-understanding. “We now have a more concrete foundation for comprehending the origins of their experiences,” notes neuroscientist Conor Liston of Weill Cornell Medicine. Despite these promising developments, past attempts to categorize autism into discrete forms have met with caution from some advocates. Amy Pearson, a psychologist at Durham University, warns, “While subtyping might seem value-neutral, it is not for everyone.”
Understanding Neurodiversity and Autism
Autism is a developmental condition influencing social interaction and engagement with the surrounding world. Autistic individuals often encounter challenges in social communication and exhibit sensory sensitivities, alongside restricted behaviours and interests. In many jurisdictions, autism is recognized as a disability, facilitating access to support services. However, a significant number of autistic individuals identify it not as a disability, but as a form of neurodivergence, while others are comfortable with both designations.
A heightened awareness of neurodiversity has contributed to an increase in autism diagnoses. Estimates in the United States now suggest that one in every 32 individuals may be autistic. This figure includes many women and girls who are often diagnosed later in life, as autism can manifest differently in them, particularly concerning social motivations and behaviour, a factor historically overlooked in diagnostic criteria.
The concept of an “autism spectrum,” first posited by psychologists in 1979, broadly accommodates this inclusive diagnostic approach, and indeed, many autistic individuals find the concept beneficial. However, the growing need to articulate the vast variations in behaviour and experience has also illuminated the spectrum’s inherent limitations.
Paul, a project manager in his early fifties, is currently navigating the diagnostic process. He describes difficulties with interpersonal skills, such as “understanding what other people are feeling” when their emotions are not explicitly stated. “It affects me at work, but it has also helped me, because I ask many questions to fully grasp a subject and will not move on until I understand it,” he explains. Due to entrenched stereotypes about the spectrum, Paul had not considered the possibility of being autistic until his therapist suggested it. “I don’t think anyone fits all these aspects,” he remarks.
According to Liston, autism functions as a broad classification encompassing “people with potentially many different molecular, cellular, and brain circuit mechanisms.” He advocates for more precise identification methods and an embrace of the condition’s heterogeneity to better understand the underlying biology. This approach, he suggests, could lead to earlier diagnoses and tailored support for autistic individuals. “Ultimately, that’s the goal,” states Adriana Di Martino of the Child Mind Institute.
Investigating Autism Subtypes
In recent years, researchers have embarked on efforts to delineate autism subtypes by identifying clusters of individuals exhibiting similar traits and symptoms, which may also share common biological underpinnings. An early exploration, published in 2020, involved developmental psychologist Mirko Uljarević and his colleagues at Stanford University. They surveyed parents of 164 autistic children regarding their children’s social abilities, identifying five clusters with distinct patterns of strengths and weaknesses across various social traits, rather than a simple continuum of severity.
It became evident, however, that this and similar studies could benefit from methodological refinements. Some research relied heavily on parental reports for autistic children, impacting reliability. Furthermore, clarity was lacking on whether these represented true clusters or if the spectrum concept better explained the data. A 2020 review led by Di Martino concluded that “at least two to four” distinct autism neurosubtypes likely exist, but acknowledged that the studies were too small and utilized qualitative measures of autistic traits.
Since then, researchers such as Di Martino have enhanced their methodologies, employing larger sample sizes and identifying more detailed behaviours and traits. They have also incorporated brain imaging and genetic analysis to correlate behaviour with biological mechanisms. “We believe this is a more effective way to understand and characterize the features relevant to autism,” Di Martino commented.
Emerging from this extensive research are what appear to be genuine subtypes. A 2023 study coordinated by Liston and his colleagues analyzed existing datasets from 432 autistic individuals whose brain activity had been measured alongside identified autistic traits. They consistently identified three distinct dimensions where brain activity and behaviour correlated within this group when compared to a control group of neurotypical individuals. These dimensions pertained to intellectual functioning, particularly verbal intelligence; social behaviour and relationships, termed “social affect”; and restricted interests and repetitive behaviours.
Based on these dimensions, the research team observed that the autistic group’s traits clustered into four subgroups. Subgroup one comprised individuals with high verbal intelligence and robust connectivity in their language-processing centers, a pattern opposite to that of subgroup two. Similarly, subgroup three exhibited poor social affect but fewer restricted and repetitive behaviours, whereas these traits were reversed in subgroup four. “Having identified those four subtypes, we can begin to ask questions about [why] they’re different,” stated Liston.
Intriguingly, the study revealed that atypical connections within a specific brain system did not necessarily lead to traits associated with that system. “A lot of work to date has tended to assume that what is causing your symptoms, or what explains the severity of your symptoms, is also somehow abnormal,” Liston explained. “And that is, in fact, not the case.” He elaborated that some neurological changes might represent compensatory mechanisms within one part of the brain for issues elsewhere, a detail that would be obscured in studies that aggregate all autistic individuals but becomes apparent through subgroup analysis.
Genetic Foundations of Subtypes
Introducing genetic factors provides further insights. Gene variants associated with autism frequently play a role in the connections between neurons, known as synapses. Liston’s team discovered that brain regions with altered circuitry in autistic individuals, compared to neurotypical individuals, also demonstrated characteristic changes in gene expression. This suggests the potential to trace a pathway from genes to brain circuitry and ultimately to behaviour, according to Liston.
Another significant subtyping study was published in July of the previous year by geneticist Natalie Sauerwald at the Flatiron Institute and her colleagues. They utilized data from Simons Powering Autism Research, a study spearheaded by the autistic community, encompassing 5,392 autistic individuals—a tenfold increase over previous cohorts. For each participant, researchers examined 239 traits across seven categories: communication, restricted and repetitive behaviour, attention, disruptive behaviour, mood, developmental delay, and self-injury. It is noteworthy that some autistic individuals view the heightened incidence of self-harm or other challenging behaviours within the autistic community as a reflection of how they are treated by a world not designed to accommodate their needs.
The research identified patterns in the combinations of these traits, revealing four naturally occurring subgroups. These differed in several aspects from the subgroups identified by Liston’s team. The first subgroup experienced significant challenges in communication, restricted or repetitive behaviours, disruptive behaviour, attention, and anxiety, but showed no signs of developmental delay. The second subgroup presented with developmental delay and a varied mixture of other traits. Individuals in the third subgroup exhibited mild difficulties across all seven categories, while the final subgroup displayed severe difficulties comprehensively.
Team member and geneticist Olga Troyanskaya at Princeton University and the Flatiron Institute commented on the researchers’ surprise at the strong emergence of the four groups from the data. “Every individual is unique, but there do seem to be these replicable groups,” she stated.
The notion that certain subtypes might involve developmental delay was further supported by a study published in October of the preceding year, which examined children diagnosed with autism between the ages of five and seventeen. Researchers identified evidence for two subgroups. Subgroup one experienced social, emotional, and behavioural difficulties early in life, whereas subgroup two exhibited increased difficulties in late childhood and early adolescence. These subgroups were also associated with distinct sets of genetic variants, although some overlap was observed between them.
Currently, it remains unclear how these and other subtyping studies integrate, or whether there are two, three, four, or more distinct subtypes. “I’ve sat down and tried to write down what each group is [in other studies] and how that fits with our groups,” said Sauerwald. She noted that some categories identified by her team are clearly distinct, while others appear to align with findings from Liston and other researchers. “We’re hopefully getting closer to the reality,” she added.
The discrepancies are not entirely unexpected, given the different research approaches employed. Sauerwald and her colleagues focused on observable traits, while Liston’s team concentrated on brain connectivity. Furthermore, the teams investigated different types of genetic variation: Sauerwald’s examined changes within the genome itself, whereas Liston’s looked at gene expression.
Shifting Subtypes Over Time
Further complicating matters is the possibility that an autistic individual might not remain within the same subtype throughout their life. “There’s a lot of clinical information pointing to changes over time and through development,” Sauerwald observed. “As kids get older, sometimes they might switch.” A 2024 subtyping study, which reassessed autistic individuals several years after an initial clustering assessment, found that nearly half had changed subgroups within a five-year period.
“I don’t think subtypes capture the multidimensionality of development,” commented Pearson, who is autistic herself. She suggests that, similar to neurotypical individuals, autistic people undergo numerous changes throughout their lives, making subgroups an inherently crude approximation of behaviour and experience.
Indeed, the existence of truly distinct subtypes remains an open question. While these studies strongly indicate that certain combinations of traits are more prevalent than others, it is still conceivable that every possible combination exists within someone, somewhere. Due to these uncertainties, none of the interviewed subtyping researchers advocate for the immediate clinical application of their identified subgroups.
Nevertheless, with continued advancements, they hope their research will offer a beneficial framework for the autistic community. Autism diagnoses already assist many individuals in understanding themselves. Breaking down the broad autism diagnosis into subtypes could help autistic people better comprehend each other’s varied experiences, thereby further validating their own, according to Liston.
In recent years, there has been increased recognition of autism and neurodivergence, partly facilitated by the internet. Finer subgroups, he suggests, would represent a natural progression of this trend. Many autistic individuals, Paul noted, are still told they cannot be autistic because they lack certain traits. Subtyping, he believes, could offer a way to state, “Well, I’m in this category.” While some may find benefit in this, he personally does not feel he needs it.
Troyanskaya envisions a future where physicians could use subtypes to provide autistic individuals or their families with advance warning of potential challenges, potentially years in advance. This foresight, she posits, would enable “having the awareness to try to get support in place before the crisis, as opposed to after the crisis.”
Another potential future development could involve targeted pharmacological treatments for specific adverse effects. This is a sensitive area, as it risks conflation with the notion of an “autism cure,” implying that being autistic is inherently negative. Many autistic individuals consider their condition a strength, as Di Martino points out. However, she argues that such treatments could be beneficial for specific behaviours like self-harm.
Tentative evidence suggests that autistic people within different subgroups may respond differently to these treatments. For instance, oxytocin, a hormone proposed to enhance social responsiveness, has yielded inconsistent results thus far. A 2024 study that categorized participants into two autism subtypes found that one subgroup responded more robustly to oxytocin than the other. This finding might help explain oxytocin’s variable outcomes, but it does not settle the debate on the necessity of pharmaceutical treatments or the societal imperative to increase support for autistic individuals.
In an online forum discussion with New Scientist, a user identified as Neonatal RRT, an autistic hospital worker, expressed concern that while more personalized healthcare approaches are superior, they also risk individuals falling through the cracks if they do not fit neatly into finer categories. “People can be denied the care they need,” they wrote.
The Legacy of Asperger’s Syndrome
Past attempts at further categorization have encountered limitations. Autism is currently recognized as an umbrella diagnosis by clinicians. However, between 1994 and 2013, psychologists identified a distinct, “milder” form of autism known as Asperger’s syndrome. This diagnosis was applied to individuals who, while possessing adequate language skills, experienced difficulties with social skills and exhibited restricted interests. Some autistic individuals continue to identify with the term “Asperger’s,” yet many eschew it, either due to its namesake Hans Asperger’s association with the Nazi child euthanasia program or because they reject the idea of dividing autistic people into groups perceived as “high-functioning” (requiring less support) and “low-functioning.” Furthermore, some individuals categorized as high-functioning often found it more challenging to access treatment and support.
Anoushka Pattenden at the National Autistic Society in the UK voices concern that this latest wave of subtyping research, despite its positive intentions, could yield similar negative outcomes. “We fear that further categorizing of autism is unhelpful and may lead to more stigma or discrimination,” she stated. Pattenden, herself autistic, appreciates that researchers in these new subcategories have avoided labels like high-functioning or low-functioning. However, she acknowledges, “you don’t have control over how that gets used, and what ends up happening with it.”
Sauerwald recognizes these potential risks and mentioned that her team consulted with the autistic community during the naming of their subgroups. “We are constantly learning and doing our best to ensure that our work is beneficial to the communities involved rather than harmful, to the extent we can,” she affirmed.
Ultimately, subtypes can only prove beneficial if societies also cultivate greater empathy towards autistic individuals, as Paul suggests, an experience he did not have while growing up. Pearson highlights that many educational institutions and employers still fail to provide general accommodations for autistic people, let alone personalized support.
“The first hoop to jump through with all of this is education,” wrote Neonatal RRT, suggesting that this is a crucial step in dismantling harmful stereotypes about autism. Instead of a universal label of being “on the spectrum,” the autistic community, in response to the diversity of their experiences, has adopted another recent metaphor: the color wheel. Each spoke of the wheel represents a unique autistic trait, such as restricted interests or sensory sensitivity, extending outward to varying degrees. In this manner, the color wheel, with its multitude of potential “plots,” underscores autistic individuality.
Sauerwald and other researchers hope that a respectful approach to subtyping can illuminate autism’s underlying biology in a way that also brings this color wheel, and the lived experiences it encompasses, into sharper focus. What we collectively choose to do with these subtypes—and how societies choose to treat neurodivergent individuals—is then our shared responsibility.