Parents who have a child on the autism spectrum are more likely than other parents to see a future child diagnosed with autism, too. A new study by Harvard researchers shows the likelihood is much higher when that older child is a girl.

The likelihood is not a certainty, though. Even when an older son or daughter was diagnosed, more than 80 percent of future children were not found to be on the spectrum.

The study found that if an older girl had autism, among her younger siblings a brother had a 17 in 100 chance of being diagnosed with autism. A younger sister had an 8 in 100 chance of being diagnosed.

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With an older boy on the spectrum, the study found 4 percent of younger sisters and 13 percent of younger brothers were diagnosed.

The researchers got their data on 1.5 million families from an insurance company, but in a study summary did not name the company. It said the data was anonymized. It thanked Aetna Life Insurance Company for supporting the study.

Overall, about 1.2 percent of kids were diagnosed with autism spectrum disorder, with boys about four times more at risk than girls.

The researchers said they hoped the results would help people to be able to more promptly screen for the condition and intervene.

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