Kids with autism often have difficulty with everyday activities like running and writing. Now, researchers say they’ve linked these motor skills troubles with the presence of autism itself.

The finding reported in the journal Autism offers firm evidence that motor skills difficulty is related to autism, not something that simply runs in families, researchers at Washington University in St. Louis said.

The study focused on 67 families, each including children with and without autism. Researchers observed the kids doing a variety of activities that rely on motor skills such as cutting with scissors, putting pegs in a pegboard and throwing a ball.

Of the children with autism, 83 percent exhibited below average motor skills. Meanwhile, just 6 percent of the siblings without the developmental disorder displayed less than average skills.

“From our results, it looks like motor impairments may be part of the autism diagnosis, rather than a trait genetically carried in the family,” said Claudia List Hilton, an assistant professor in occupational therapy at Washington University and the study’s lead author. “That suggests that motor impairments are a core characteristic of the diagnosis.”

What’s more, Hilton and her colleagues noted that the degree to which children with autism displayed difficulty with motor skills correlated with the severity of their autism and the extent of their social skills deficits.

“Kids who have difficulty with motor skills might have trouble with what we think are simple things like brushing their teeth, buttoning, snapping or starting a zipper — things that are so basic to being independent, but would cause other problems at school,” Hilton said. “They would need to have an aide or someone helping them, and that would set them off as different from the other kids.”

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