RUBI Paice looks like a typically energetic toddler as she bounds around her garden – but the brave three-year-old faces a gruelling daily battle with a life-threatening illness so rare she is thought to be the only person in the UK who has it.

Her immune system is attacking her kidneys at such a rate that she will be dependent on renal dialysis and need a life-saving transplant by the time she is five.

The deadly disease, for which there is no cure, could have been triggered by something as minor as a common sickness bug or tonsillitis.

It has left Rubi at higher risk of heart failure because the levels of potassium – the mineral that conducts electrical impulses to the muscles – in her body are so high. This means she can only have ice-cream, milk and chocolate, which are high in potassium, as a special treat, for fear it could kill her.

But Rubi, who has been in hospital more than 10 times and endured about 50 blood tests in the last eight months, continues to amaze everyone with her resilience.

Mother Denise Paice, from Inverurie, Aberdeenshire, said: “You’d think there was nothing wrong with her. She’ll jump off the sofa onto cushions and run around with her brothers. Sometimes I look at her and think, ‘How can she be so ill?’ But we’ve been told by this time next year, if she’s not on dialysis she’ll be one of the lucky ones.

“If she got something like measles, that’s all it could take to send her kidneys into complete failure. And because her immune system is compromised, she hasn’t been able to complete the immunisation programme.”

The family’s ordeal began in April when Rubi woke up one morning with a swollen face. Mrs Paice, 41, said: “She climbed into bed beside me and I didn’t recognise her. Her eyes were almost closed and her face was very puffy. I initially thought she might have had an allergic reaction. Then I noticed her nappy was dry, so I texted her dad to ask if he had changed her before he left, but he said he hadn’t.”

Rubi had also developed skin creases on her wrists. Mrs Paice made an appointment to see the GP and Rubi was admitted to hospital that morning.

At first, medics thought she had nephrotic syndrome, a treatable kidney condition which is often outgrown by adulthood. But 10 days later, her mother and father Taran were told she was showing signs of a more serious illness called focal segmental glomerulosclerosis (FSGS).

Mrs Paice said: “Her blood and protein levels were through the roof and her tummy was so swollen she was struggling to move around. We were absolutely in shock. She was put on steroids in the hope it would help stop the immune system from attacking the kidneys but this never worked.”

At the end of May, Rubi was transferred from the Royal Aberdeen Children’s Hospital to the Royal Hospital for Children in Glasgow for a kidney biopsy. But the results did not show the typical signs of the disease.

Ten days later doctors confirmed Rubi had collapsing FSGS, which is much rarer and more deadly. She also had the most aggressive form of this variant of the disease, and Mrs Paice has been told that by the time Rubi starts school she will probably be dependent on renal dialysis to keep her alive.

She will join other kidney patients on the transplant register in the hope a donor organ being found. Mrs Paice, who, along with her husband, 37, will also be tested to see if she is a match for her daughter, said: “Our whole world has been turned upside down. Until eight months ago we had a perfectly healthy two-year-old. “And as much as I would love to wrap her up in cotton-wool, I can’t. We have to weigh up the risks with her quality of life.She’s only three and she needs to be go friends. But every day is worry.

“We don’t know what the future holds for Rubi. We just take it one day at a time and are making sure there are lots of happy memories.”

Her parents have set up a Facebook page, Rubi’s FSGS Journey, to raise awareness of the disease.