Researchers Say There Are 4 Types of Autism

Autism has long been known as a spectrum, signifying a wide range of symptoms and severity. Now, new research suggests that spectrum is made up of four distinct forms, each with its own pattern of behaviors and genetic signatures, per the Washington Post. The four categories emerged from a study published in July in Nature Genetics, led by researchers at Princeton University and the Flatiron Institute, who analyzed data from more than 5,000 children. One group, representing about 10% of autism cases, experiences pervasive developmental and communication challenges, according to the study. Another, roughly 19%, shows early developmental delays but relatively fewer mood or behavior issues.

A third, about one-third of the sample, has the classic social and communication differences associated with autism, but without developmental delay. The largest cluster, around 37%, meets milestones on time but later develops issues such as ADHD, anxiety, depression, or obsessive-compulsive symptoms. There is still much variation within the groups, per Scientific American. But the findings reinforce a growing view among scientists that "autism" is an umbrella term covering separate biological conditions that unfold on different timelines. For parents of children with autism, the new framework indicates a complexity to the disorder that feels overdue. As one of the lead authors said, "There are many autisms," not just one.

The research is backed up by a separate Nature paper published this fall, using independent datasets from the US, Europe, and Australia. It reported that children diagnosed after age 6 tended to have forms of autism genetically distinct from those marked by early-childhood developmental delay, with a presentation that overlaps with other mental health conditions. Researchers say this emerging picture helps explain why the spectrum has been so hard to define and why the number of diagnosed children—now about 1 in 31 in the US, up from 1 in 150 in 2000—has climbed as criteria have broadened and awareness has grown.

Scientists stress that genes are only part of the story. Hundreds of genetic variants have been tied to autism, some inherited and others arising spontaneously, and multiple teams are probing how prenatal and environmental factors might influence when and how those genes act. Early work points to possible roles for chemical exposures, medications, and the timing of events during pregnancy, though most observed links are modest and not considered definitive, per the Post. Meanwhile, brain research is tracing how these influences may alter development, from the density of synapses to biochemical pathways.