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The Auckland girl wolfed down anything she could lay her hands on - cake and sausages if she was lucky - and loved swimming and ball games.
"If you ever started a sentence with 'who wants' she would say 'me' before you even finished," her mum, Lisa Archer, said.
"She knew the alphabet, could count to 20 and loved singing the national anthem and ABBA songs."
Now, that cheeky little girl that used to bang her breakfast plate against the side of her parent's bed, demanding to be fed, likely won't see her 10th birthday.
She can't talk, or make any controlled noise, nor can she support herself, or register any head control whatsoever.
Katie is blind, completely tube-fed, and, battling serious respiratory issues, is on oxygen most of the time.
Lisa and husband Brett don't know whether their daughter can still hear them.
"One of the hardest things for me is can she understand me? Does she know it is me?"
That's the cruel hell of late infantile Batten disease - a rare, neurodegenerative, incurable and ultimately fatal condition that Archer calls the antithesis of those parental instincts of protecting and nurturing a child, and watching them grow.
Each year, four more Kiwi kids are diagnosed with it.
Few live past 10.
But now, New Zealand researchers are reporting promising early findings focused on factor that led to Katie's diagnosis: her genes.
For children to develop the disease, both parents must be carriers of a genetic mutation, something Katie's parents had been blissfully unaware of until 2011, when she began having seizures, losing her speech and falling over.
A visit to a neurologist raised the improbable possibility of Batten disease; months of trips to Starship Hospital ultimately confirmed it.
"We searched worldwide for trials or potential treatments, we were prepared to do anything, but there was absolutely nothing," Mrs Archer said.
"We were devastated and nothing can prepare you for knowing there is nothing you can do to help your child."
But, she hopes, they may be something she can do for other kids.
The family have been working with researchers at University of Otago and Lincoln University toward a new gene therapy - and the key to a cure could lie in our sheep.
So far, more than 400 mutations in 13 different genes have been identified which cause the various forms of the disease.
Otago University's Dr Nadia Mitchell and her fellow researchers have been trialling a gene therapy strategy involving the replacement of a defective gene with a functional one.
Modified viruses carrying a corrective copy of the mutated Batten disease gene are injected into the fluid filled spaces in the brain, before "infecting" the brain cells and using them to make functional protein, which can correct or stabilise the disease.
The researchers have been working with sheep as the animals shared many of the clinical and pathological features of the human disease, including neurodegeneration, blindness and premature death.
Dr Mitchell and her colleagues have been able to show how a one-off treatment of gene therapy to pre-symptomatic sheep with one form of Batten disease protected them against it setting in and progressing.
The treated sheep showed no neurological decline and, apart from a late-onset loss of vision, the sheep were indistinguishable from normal animals and their lifespan was extended.
Another trial targeted at sheep with early symptoms has showed the disease stabilising the disease for more than a year, halting further decline.
Further trials were now planned for other forms with the disease, with an ultimate aim to provide compelling evidence it worked, and then push for a clinical trial with US collaborators.
"Given early enough, I think gene therapy has a real chance of preventing this disease," Dr Mitchell said.
"Although a one-off 'cure' would be the dream goal, anything that can extend the lifespan and improve the quality of life for affected children and their families would be amazing."
Mrs Archer agreed.
"This is too late for Katie. But I want to help in any way I can to ensure no other families have to go on this horrendous journey."
The new insights come as charity Cure Kids, which has already invested $360,000 in the programme, are again calling on Kiwis to help them raise $1 million to support sick children like Katie.
Its annual Red Nose Day appeal runs the whole of this month, 800 schools, 400 businesses and 500 volunteers from around the country taking part.
Taking the lead are celebrity couple and Cure Kids ambassadors Art Green and Matilda Rice, who will both dye the tips of their hair red ahead of the official Red Nose Day, on September 29.
People can support the appeal by visiting the website www.rednoseday.co.nz, and following it on Facebook, Instagram, Twitter and YouTube, with the hashtags #poseforrednose and #rednosedaynz.