The discovery of four different subtypes of autism is a major step toward understanding the condition's genetic underpinnings and improving care, researchers reported in Nature Genetics.
According to researchers, the four autism subtypes can be categorized as: Behavioral Challenges, Mixed Autism Spectrum Disorder with Developmental Delay, Moderate Challenges, and Broadly Affected. Each subtype exhibits distinct developmental, medical, behavioral and psychiatric traits, and importantly, different patterns of genetic variation, the researchers said.
The findings are drawn from a study of more than 5,000 children with autism, ages 4 to 18, and nearly 2,000 of their nonautistic siblings. The study looked for nearly 240 traits in each individual, from social interactions to repetitive behaviors to developmental milestones.
While the four subtypes may share some traits – like developmental delays and intellectual disability - the genetic differences suggest distinct mechanisms are behind what appear on the surface to be similar characteristics.
The timing of genetic disruptions and the effects on brain development differ with each subtype, researchers found.
As a result, some of the genetic impact of autism may occur before birth while other effects may emerge as children grow.
"What we're seeing is not just one biological story of autism, but multiple distinct narratives," study co-leader Natalie Sauerwald of the Flatiron Institute in New York said in a statement.
"This helps explain why past genetic studies (of autism patients) often fell short," she said. "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."
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