Within months, Tillie Mae Mawdsley, four, could be so stiff the only way she will be able to move is if her parents bend her limbs by hand like a model in a shop.
Even more heartbreakingly, Tillie is expected to die from the cruel illness before she is 14-years0old – unless a cure is found.
But the fact is that a cure does exist – but not in the UK. Now Tille's mum and dad, Michala, 32, and Paul, 36, have launched a fund to pay for the treatment their daughter so desperately needs.
Michala said Tillie has now become so ill she has stopped speaking.
"She has started to become stiff - her left foot bends in and she cannot lift her arms above her head," she said.
"She will become like a mannequin in time - so stiff she can only move with our help.
Tillie, who lives with her parents and sister Lexie, six, in Hatfield, Herts, was diagnosed with Sanfilippo syndrome when she was just two.
Her parents have launched a fundraising drive to pay for the £580,000 drug trials for the wonder cure which could make it available to Tillie.
The drug, Genistien, - found in soy foods and relatively cheap - could delay the progression of the disease. Developed at Manchester Children's Hospital it has already been used to good effect in the USA.
But because the condition only affects a handful of children in Britain each year, funding for clinical trials for NHS use has not been provided.
A group of families are now trying to raise £580,000 to fund the clinical trial at Manchester Children's Hospital with the help of new charity Wicked Genes.
Michala, who has set up a fundraising page for Tillie with Paul, said: "We are so desperate to get this money. The drug would mean the world to us."