Researchers have taken a “transformative step” towards understanding the biology underlying autism after discovering four subtypes of the genetic condition.
Scientists at Princeton University and the Simons Foundation analysed data from 5,000 children in SPARK, an autism cohort study, to group individuals based on their combination of traits.
Instead of searching for genetic links to certain traits, researchers considered a range of over 230 traits in each individual, from social interactions to repetitive behaviours to developmental milestones.
From this analysis, they were able to identify four subtypes of autism with different patterns of genetic variation.
“What we're seeing is not just one biological story of autism, but multiple distinct narratives," said Natalie Sauerwald, associate research scientist at the Flatiron Institute and co-lead author.
“This helps explain why past genetic studies often fell short—it was like trying to solve a jigsaw puzzle without realizing we were actually looking at multiple different puzzles mixed together. We couldn't see the full picture, the genetic patterns, until we first separated individuals into subtypes.”
The four subtypes were Social and Behavioral Challenges, Mixed ASD with Developmental Delay, Moderate Challenges, and Broadly Affected.
The first type relates to children reaching developmental milestones at a similar pace to children without autism, but they often experience co-occurring conditions like ADHD, anxiety or depression.
The second type showed a delay in reaching developmental milestones but with no signs of co-occurring conditions.
The third type, Moderate Challenges, shows core autism-related behaviours but less strongly than other groups, reaching milestones at a similar pace to children without autism and with no co-occurring conditions.
The fourth type faces the most extreme and wide-ranging challenges.
The first and third types were the most common, with 37 per cent and 34 per cent of participants found to be in each group, respectively, while the second and fourth types were the least common, with 19 per cent and 10 per cent of participants in each group.
The findings highlight how genetic differences “suggest distinct mechanisms behind superficially similar clinical presentations”.
For example, children in both the Broadly Affected and Mixed ASD groups share some important traits, such as developmental delay and intellectual disability, but the former group showed the highest proportion of de novo mutations, which are not inherited from either parent, whereas the latter group was more likely to carry rare inherited genetic variants.
The findings do not mean there are only four subtypes of autism; they establish the discovery of a data-driven framework showing there are at least four, and that they are meaningful both for clinical work and research at the genome level.
For families navigating autism, knowing which subtype of autism their child has can offer new clarity, tailored care, support and community.
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