Two attendees of the Autism Self-Advocacy Network in New Westminster, British Columbia, Canada, play with a "stimming" toy called a Tangle on June 18. The gadget allows autistic people to fidget, creating a sense of comfort. (Ben Nelms for The Washington Post)

Researchers looking into mortality trends and autism have made a troubling discovery: People on the autism spectrum are dying young — some 12 to 30 years earlier than might otherwise be expected.

The analysis, conducted by Sweden's Karolinska Institute and published in the British Journal of Psychiatry, found that the leading cause of premature death in autistic adults isn't due to diseases, such as heart ailments or cancer, that are the main killers in the general population. It's suicide.

The data, which includes information on 27,000 people with the social-communication disorder and about 2.5 million who do not have the diagnosis from Sweden's national registries, found that, on average, autistic adults die 18 years younger than their non-autistic counterparts.

An autistic person's age at death also appeared to be impacted by cognitive ability. Those with autism and a learning disability died 30 years earlier on average while those without intellectual impairment died 12 years earlier. Individuals considered to be on the "high-functioning" end of the spectrum with strong language skills — those who might have been diagnosed with Asperger's before the diagnostic criteria changed — still had double the risk of dying young as those without the condition.

The overall trends were similar for both genders, but autistic women with learning disabilities had the highest risk of premature death of any of the subgroups.

"This new research confirms the true scale of the hidden mortality crisis in autism," said Jon Spiers, chief executive of Autistica, an autism charity in Britain. "The inequality in outcomes for autistic people shown in this data is shameful. We cannot accept a situation where many autistic people will never see their 40th birthday."

Experts theorized that both biological and social factors may be contributing to the higher risk of premature death. Some studies have suggested a link between the genes leading to autism and those related to epilepsy, mood disorder and anxiety disorder. Indeed, the Swedish analysis found that up to 40 percent of people with autism also suffer from epilepsy. People with autism may also differ from those in the general population by having a more restricted diet, limited access to exercise and increased use of medication.

A report published this week by Autistica based on the Swedish study also noted significant "social and cultural pressures." It singled out bullying, pressure to conform (which can result in ‘masking’ serious problems) and social isolation as being part of the mix of things that may contribute to a person's early death.

The data shows that adults with autism and no additional learning disability are over nine times more likely to commit suicide. The rate is shockingly high, but not inconsistent with previous research that estimates that 30 to 50 percent of autistic people have considered committing suicide. There's evidence that diminished sense of self-worth begins in childhood. One study found that while only 0.5 percent of typically developing children experienced suicidal thoughts, 14 percent of those with autism had.

Calling the problem a "hidden crisis," Spiers announced at a briefing in London this week that the organization is seeking to raise funds to launch a five-year, $14.5-million research program to investigate why autistic adults are dying so young.

In the United States, the prevalence of autism has been growing in recent decades. The Centers for Disease Control and Prevention estimated in 2014 that 1 in 68 children have the condition.

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