Now, a new study published in Nature Genetics expands the contours of the autism spectrum by identifying four clinically and biologically distinct subtypes of the condition.
“The research highlights that there are indeed different types of autism that carry different clinical, genetic, and biological profiles,” says the study’s coauthor Jennifer Foss-Feig, PhD, a clinical psychologist at the Seaver Autism Center for Research and Treatment at the Icahn School of Medicine at Mount Sinai in New York City.
“When someone with autism or their caregiver wonders how two people with autism can be quite so different — in development, in symptoms, or in support needs — this research suggests that it’s because they are different,” explains Dr. Foss-Feig, who serves as the vice president and senior scientific officer at the Simons Foundation Autism Research Initiative (SFARI).
4 New Autism Subtypes
Autism is characterized by a range of characteristics related to difficulties with social communication and interaction, and restricted and repetitive patterns of behaviors, activities, and interests. These characteristics can vary in intensity and presentation from person to person.
“They may have different subtypes of what we currently lump together as autism spectrum disorder,” Foss-Feig says.
The new research analyzed data from more than 5,000 autistic children ages 4 to 18 in SPARK, a nationwide cohort study collecting and tracking genetic and clinical presentations via questionnaires filled out by their parents.
Using a person-centered analysis, researchers considered more than 230 traits, including social interactions, repetitive behaviors, and developmental milestones. Then they used a computational model to group individuals based on trait clusters.
The analysis identified four subtypes — each with distinct developmental, medical, behavioral, and psychiatric traits, as well as genetic and biological patterns, says study coauthor Olga Troyanskaya, PhD, director of Princeton Precision Health and a professor at the Lewis-Sigler Institute for Integrative Genomics at Princeton University in New Jersey.
The study is an important step in understanding autism’s genetic relationships and the potential for personalized treatments, Dr. Troyanskaya says. “This is a major advance,” she adds, showing how biological differences could relate to someone’s individual autism presentation.
“This is important research because it’s another brick in the wall of building the foundation of answering important questions” about autism, says Raymond Romanczyk, PhD, a psychology professor and co-director of the Institute for Child Development at Binghamton University in New York, who wasn’t involved in the new study.
Here’s an overview of the subtypes:
Social and Behavioral Challenges
This group made up 37 percent of study participants. Children in this group had social challenges and repetitive behaviors, but generally reached developmental milestones similarly to children without autism. They also typically had co-occurring conditions like ADHD, anxiety, depression, or obsessive-compulsive disorder.
Mixed ASD With Developmental Delay
This group represented about 19 percent of participants. These children usually reached developmental milestones like walking and talking later than children without autism. However, they didn’t exhibit signs of anxiety, depression, or disruptive behaviors. Some experienced repetitive behaviors and social challenges.
Moderate Challenges
Representing about 34 percent of study participants, this group showed core autism behaviors, but not as strongly as other groups. They also usually reached developmental milestones on a similar timeline to children without autism and didn’t have co-occurring psychiatric conditions.
Broadly Affected
This group accounted for 10 percent of study participants. These individuals experienced more severe and wide-ranging challenges, such as developmental delays, social and communication difficulties, repetitive behaviors, and co-occurring psychiatric conditions, including anxiety, depression, and mood dysregulation.
Each Autism Subtype Had Distinct Genetic Features
There is no single known cause of autism. While there are likely many causes, scientists know that genetics play a role. Currently, though, genetic causes can only be identified in about 20 percent of cases.
The new study linked the four subtypes to distinct types of genetic mutations and biological pathways.
“If we know what types of genes are affected and when and where they’re expressed, then we learn more about the biology underlying different types of autism,” Foss-Feig says. “This is key to the goal of precision medicine, where treatments can be tailored — or foregone — based on knowing more about the individual’s genetics, development, and clinical profile.”
For example, children in the Broadly Affected group had the most non-inherited genetic variation in autism-related genes, Foss-Feig says, whereas kids in the Mixed ASD with Developmental Delay group had the most inherited rare variants associated with autism. In other words, children in these two groups shared some symptomatic traits — but, their genetic differences suggest the biological mechanisms behind their autism traits aren’t the same.
This is significant, Dr. Romanczyk says, because it highlights that there is “not just one thing” that potentially causes autism. He hopes that the study will help further dispel misinformation about autism causes, such as the incorrect assertion that it’s linked to childhood vaccines.
The Study Does Have Limitations
The current study included autistic children ages 4 to 18, with an average age of 8.5. Troyanskaya says a “follow-up investigating these stubtypes in adults would be very interesting.”
While the study could set a foundation for how autism is diagnosed and treated in a more personalized way in the future, Roth says more research is needed.
“As with any early-stage research, the findings from this study will need to be replicated in large-scale and more diverse populations — as well as supplemented with objective, clinician-reported data, not just parental reports,” she adds.
There Could Be More Autism Types
While the study defined four subtypes of autism, researchers say it doesn’t mean there are only four groups, Foss-Feig says.
“As more data become available, especially with more detailed clinical information about individuals’ development, growth, and challenges over time, I expect these subtypes will become more refined and additional subtypes will emerge,” she explains.
This research provides a framework for identifying additional subtypes, Foss-Feig says.
“These subtypes align with a view of autism as a complex, multidimensional condition rather than a simple line of severity,” Troyanskaya says. “The subtypes each represent unique sets of traits, with the biology of autism that the field has previously identified ‘dividing’ into parts among these subtypes.”
The research is a “step forward” in how autism is understood, including how underlying genetic variations could account for the “diversity across the spectrum,” says Kristyn Roth, chief marketing officer of the nonprofit advocacy group Autism Society of America.
“Autism is not one singular experience, but a highly variable spectrum with different presentations, strengths, challenges, and support needs,” she says.
Knowing more about autism subtypes will help clinicians make more accurate diagnoses that better account for an individual’s unique development and symptoms, Foss-Feig says. And, if clinicians have information about a patient’s genetics, it could offer clues into the most appropriate diagnosis and symptoms to pay attention to.
“Down the road, the hope is that more precise diagnoses will map to more precise treatment and support plans,” she explains.
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