A new study shows that mothers of children with autism earn 56 percent less on average than moms with typically developing kids, but the reason why might come as a surprise.

Rather than difficulties related to the autism diagnosis itself, researchers behind the new study say they believe the lack of support available for kids with autism — even as compared to those who have other types of disabilities — is likely the reason behind the stark income disparities uncovered.

For the study published Monday in the journal Pediatrics, researchers analyzed data from a national government survey of families of nearly 70,000 kids including 261 with autism and 2,921 with other health limitations.

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They found that while mothers of children with autism were likely to be older and more educated than other moms, these parents consistently earned less money. Even as compared to mothers of kids with other health limitations, moms dealing with autism took home 35 percent less, the study found.

Overall, the toll was significant, with families that included a child with autism taking in 28 percent less income on average than families with typically developing kids.

“It’s really just a hit in income,” says David Mandell of the University of Pennsylvania and the Children’s Hospital of Philadelphia who served as the study’s senior author. “I expected just from interacting with so many families with autism that we would have mothers leaving the workplace, but I did not expect the income difference.”

Interestingly, Mandell points out that mothers of kids with autism are only 6 percent less likely to be employed, but the dramatic disparity in earnings resulted from these moms working in lower wage jobs or working fewer hours. He believes the trends are due to the demands placed on parents when the treatment approach for their child is unclear.

“Raising a child with a disability is hard, but for children with many disabilities there’s a clear system. For kids with autism there’s a lot less known about what they should get and there’s a lot of disagreement about who should provide it,” Mandell said.

As a result, parents spend significant time negotiating for services and carting their children to a variety of providers which limits the time they can devote to work, he said.