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... Why it matters: The findings come as Health Secretary Robert F. Kennedy is pushing federal efforts to identify an "environmental" cause for increased autism incidence by September.

Driving the news: A Princeton-led research team examined data from more than 5,000 children in SPARK, an autism cohort study funded by the Simons Foundation.

- - - After analyzing more than 230 traits including social interactions and repetitive behaviors, they identified four subtypes: "social and behavioral challenges," "mixed ASD with developmental delay," "moderate challenges" and "broadly affected."

- - - They then linked the subtypes to distinct genetic mutations, identifying divergent biological processes in each.

- - - For example, children in the "broadly affected" group showed the highest proportion of mutations not inherited from either parent, while the "mixed ASD with developmental delay" group was more likely to carry rare inherited genetic variants.

- - - Autism is known to be highly heritable, with many implicated genes. But the researchers said standard genetic testing only explains about 20% of cases.

What they're saying: "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, in a statement. ...