A five-year-old must a daily cocktail of drugs to avoid her body turning - into a crystal.
Little Lillie Sutcliffe has a faulty kidney which fails to clean her blood - allowing excess a chemical called cystine to build up in her system.
If too much cystine remains, her cells start to solidify.
But to mother Laura Milner and father Simon Sutcliffe, she is their perfect little girl, who has battled against all odds to try and live a normal life.
Lillie, from Castleford, was diagnosed with Cysitinosis in August, 2006, at the age of 23 months old.
The incurable condition means Lillie has stunted growth, cannot walk long distances or do any sports.
And with her daily dose of drugs, she is under attack from her own body as the very cells in her tiny 86cm tall frame slowly turn to crystal.
Her parents had been worried about her growth as she looked like a baby at a year old, was constantly crying and had little appetite.
But medics stunned mother Laura, an NHS secretary, when they identified the problem after scanning Lillie's eyes and discovering the crystals.
She said: 'I had never heard of the condition so was a bit shocked to hear what it did.
'It means Lillie's body essentially turns to crystal.
'They just load up inside her, if it wasn't treated she would turn into stone eventually because it attacks all the cells.
'She can't do normal things that other five-year-olds do because she is so small - she's got the body of a two-year-old.
'She goes to full-time school and is academically no different, she just needs a step to reach things because she's so little.'
Laura, 29, added: 'It's unusual because she doesn't like sweets or anything like that because she craves salt, because she loses so much of it through her kidney.
'I have to make her salty food to try and help her replace the sodium she needs.
'If it had gone undiagnosed parts of her body would have turned to crystal.'
The condition occurs when the mechanism removing excess cystine - an amino acid - from the body breaks down.
It is then the cystine crystals build up in cells in the body, causing problems in the kidney, thyroid gland, eyes and liver.
Impaired growth is yet another symptom of the condition, which shortens life expectancy and causes sufferers to have to have a kidney transplant at some point in their lives.
Lillie has it because of the combination of a recessive faulty gene in both of her parents and sufferers can never completely rid their bodies of crystals.
Every day she has to take multiple doses of potassium citrate, sodium chloride, phosphate solution and vitamin D just to replenish her body with nutrients.
Consultant paediatric nethrologist Dr Kay Tyerman said while the illness could be partially treated, it could not yet be completely cured.
She said: 'This is an excessively rare condition. It's usually present in children who are not growing properly in the first few years of their life.
'They have a salt-wasting problem which means the kidney loses salt in the urine that she needs to help her grow.
'Lillie has such a strong craving for salty foods because she is losing so much salt her body needs to keep.
'Over the past few years she has been working on her medication, which she needs to take a lot of every day.
'The condition does cause kidney failure and can also cause blindness and it is an illness that unfortunately does tend to shorten life expectancy.
'But Lillie is a real star and just gets on with it - she is very brave.'
There are only 2,000 known sufferers of cysitinosis throughout the world, meaning Lillie is one in just 3, 353, 496.
Lillie's parents Laura and Simon, who works as a tiler for a maintenance company, separated four years ago and it was thought her behavior was down to the break-up.
But tests revealed the truth and two months after starting medication she started showing improvement.
Laura added: 'I am so proud of how she is fighting it.
'It is just a part of life now for her, we have to take every day and month one at a time, but who knows what treatment might become available in the future.
'Science is getting better and better so you never know what might be around the corner.'