Celine Dion's condition is progressing one year after she disclosed her stiff-person syndrome diagnosis.

Her sister, Claudette Dion, revealed in a new interview that the "My Heart Will Go On" hitmaker is experiencing a loss of control over certain body movements, which she described as a heartbreaking development for someone as disciplined and hard-working as Dion.

"She doesn't have control over her muscles," Claudette told 7 Jours, via translation from French, of Dion's current condition.

Claudette emphasized the rarity of Dion's illness, stating, "Because it's one in a million cases, scientists don't have that much research on the topic, because it didn't affect that many people."

Claudette said their dream is for Dion to eventually return to the stage but added, "In what capacity? I don't know."

According to Johns Hopkins Medicine, stiff-person syndrome is a rare autoimmune neurological disorder that causes muscle stiffness and painful spasms. Other possible symptoms include an unsteady gait, double vision, and slurred speech.

It is believed to affect one or two people in a million and twice as many women as men.

Although there is no cure, specialists can help manage the symptoms of the disorder.

Dion, 55, has been grappling with uncontrollable muscle spasms for some time, leading to the cancellation of her tour dates in January last year and, later, all future tour dates in May this year.

Celine Dion
Frazer Harrison/Getty Images

In May, Dion said in a message to fans via Instagram, "I'm working really hard to build back my strength, but touring can be very difficult even when you're 100%."

Dion went on to explain that she decided to cancel all her shows because it was unfair to her fans to keep postponing her concerts. But she said she was doing her best to overcome her illness and that she intended to continue her tour in the future.

"I want you all to know, I'm not giving up... and I can't wait to see you again!" Dion added.

According to Claudette, who is also a singer, Dion continues to receive an outpouring of love and support from fans, as well as messages and gifts.

"If you only knew how many calls we receive at the Foundation to hear from Céline. People tell us they love her and pray for her. She gets so many messages, gifts, blessed crucifixes," said Claudette, who is the CEO and spokesperson for the Fondation Maman Dion, an organization founded by their mother that helps disadvantaged kids.

Claudette previously shared with Le Journal de Montreal that Dion is receiving care from specialists and that their sister Linda is staying with the singer.

Meanwhile, Dion was spotted watching a hockey game with her 22-year-old son René-Charles and 13-year-old twins Nelson and Eddy in late October.

Footage shared online showed Dion meeting and posing for photos with Montreal Canadiens coach Martin St. Louis.

While the prospect of a return to the stage remains uncertain, fans can watch the Grammy winner in her first acting role in the movie "Love Again," released in May.

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