Celine Dion’s sister says the singer is suffering uncontrollable “spasms” as she continues to battle her incurable stiff person syndrome.

The ‘My Heart Will Go On’ singer, 55, revealed her diagnosis in December, which forced her to pull the plug on her ‘Courage World Tour’, and her older sibling Claudette Dion, 74, has now said she is devastated there seems little she and the singer’s family can do to help her “strong” sister or “alleviate her pain”.

Claudette told HELLO! Canada: “She’s doing everything to recover. She’s a strong woman.

“It’s an illness we know so little about. There are spasms – they’re impossible to control.

“You know who people often jump up in the night because of a cramp in the leg or the calf? It’s a bit like that, but in all muscles.

“There’s little we can do to support her, to alleviate her pain.”

She added mum-of-three Celine’s family is “crossing our fingers that researchers will find a remedy for this awful illness”.

Stiff person syndrome is a rare, progressive neurological disorder that can cause stiff muscles in the torso, arms and legs – and affects about one in a million people.

Celine’s other sister Linda and her husband have moved into the singer’s home in Las Vegas to care for her, and Claudette added: “It’s comforting for us all (to have them near Celine.)”

Claudette has previously revealed that despite working with “the top researchers in the field”, Grammy-winning Celine has seen little improvement in her health.

She told Le Journal de Montreal: “We can’t find any medicine that works, but having hope is important.”

Claudette said Celine cancelling her ‘Courage’ tour was a necessary move for her chances of rehabilitation.

She added about the singer – whose music producer husband René Angélil, 73, died in 2016 after they were married for 22 years: “I honestly think that she mostly needs to rest. She always goes above and beyond, she always tries to be the best and top of her game. At one point, your heart and your body are trying to tell you something. It’s important to listen to it.”