Man with Celine Dion's rare disease warns her comeback could be dangerous

A former marathon runner who was diagnosed with the same condition as Celine Dion worries that crowds could be a "trigger" during the singer’s recently announced comeback.

Jon Kelf, 56, was a five-time marathon runner before he was diagnosed with stiff person syndrome (SPS) in 2019, SWNS reported. Dion revealed her own diagnosis in late 2022.

SPS causes progressive muscle stiffness and severe muscle spasms that can lead to chronic pain, falls and loss of mobility over time, according to UT Southwestern Medical Center.

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"In some cases, spasms are so severe that they can cause falls, broken bones and dislocated joints," the center notes on its website.

While this rare condition is not fatal, its symptoms can dramatically affect a person’s quality of life.

The disease is often triggered by emotional stress or noise, elements Kelf calls "particularly debilitating." He shared with SWNS that he never expected Dion to perform again.

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 "I was a bit surprised. Especially when she talked about the dancing. I couldn’t dance before the diagnosis, let alone afterwards," said Kelf, who has no medical involvement or knowledge of Dion's case personally.

"Obviously, she has the resources to get the best treatment available, but even still, it’s quite remarkable."

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In 2019, the former engineer started feeling his legs tighten up and stiffen anytime he was nervous or tense, but dismissed the odd sensations until one day, he stood and couldn't move.

Kelf can now barely walk and has been forced to quit his job.

Dion has announced 10 shows in September and October at the 40,000-capacity Paris la Défense Arena, planned at three- to four-day intervals. 

The intervals will be crucial for Dion to pace herself, rest and medicate between shows, according to Kelf.

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"Everyone’s different, but I’m still surprised," said Kelf, who added that the disease could "limit" the singer.

"It’s challenging to live with, to say the least. You have to rearrange your entire life. There are good and bad days."

While Kelf is hopeful that Dion will be able to make the show work, he warned against underestimating the seriousness of the disorder.

"I think it could undermine how seriously people take us, other sufferers," he told SWNS.

While he views the tour as positive and inspiring, Kelf said he hopes it will lead to more support for others who are suffering.

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"Otherwise, people may look at her and think, ‘Why aren’t I doing more?’ which could ultimately have a negative impact."

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"If I’m out in public, people don’t see the worst of it," he added. "It's the same with her, they only see the good side."

Fox News Digital reached out to Dion's representatives for comment.