“She’s working hard, but she doesn’t have control over her muscles,” Claudette Dion told Canada’s 7 Jours, per the Daily Mail. “What breaks my heart is that she’s always been disciplined. She’s always worked hard. Our mother always told her, ‘You’re going to do it well, you’re going to do it properly.’”

Last December, the 55-year-old “My Heart Will Go On” singer shared that she had been diagnosed with the incurable neurological condition, and was cancelling her forthcoming tour dates.

Then in May, Dion was forced to pull the remaining dates of her world tour. The Canadian musician said that she was “working really hard to build back my strength”.

She added: “I’m so sorry to disappoint all of you once again. It’s not fair to you to keep postponing the shows, and even though it breaks my heart, it’s best that we cancel everything now until I’m really ready to be back on stage again.”

However, in the new interview, Dion’s sister played down the possibility of her returning to full-scale touring. “It’s true that in both our dreams and hers, the goal is to return to the stage,” she said. “In what capacity? I don’t know.”

Celine Dion performing during the Billboard Music Awards in Las Vegas in 2017 (Ethan Miller/Getty Images)

Claudette Dion added that the rarity of the condition means there has been scant research into a cure: “The vocal cords are muscles, and the heart is also a muscle. This is what comes to get me. Because it’s one out of a million case, the scientists haven’t done that much research because it didn’t affect that many people.”

She added that, nevertheless, Celine and her family remain hopeful: “Some people have lost hope because it’s an illness that isn’t well known. If only you knew the number of phone calls the Foundation gets about Celine! People tell us they love her and they’re praying for her. She gets so many messages, presents and blessed crucifixes.”

SPS is an autoimmune and neurological disorder that causes rigidity in the torso and limbs. Symptoms also include muscle spasms, which have affected Dion’s ability to sing and perform, and can be triggered by environmental stimuli (like loud noises) or emotional stress.