"People generally cannot live independently with Prada Willi because of their compulsion to eat, they have to have food locked up and monitored."
Mrs Arnott said Josie, now 12 weeks old, has "no appetite, but it comes to a point, any time from age 2, where they're hungry all the time".
"The idea of being hungry is awful. I know I'm really grumpy when I'm hungry, imagine that all the time."
According to Mrs Arnott, Josie was a "very content baby".
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"She's very calm, she hardly ever cries, which is part of the syndrome. She also just doesn't have the energy to cry."
The rare disease could affect one in 15,000 to 20,000 people.
When the Arnotts decided to start a fundraiser to enable the Foundation for Prader Willi-Research to conduct a study on the benefits of oxytocin hormone treatment for those with Prader Willi Syndrome, they decided to do it slightly differently.
"As we learnt about the syndrome I guess we were hopeful there would be treatment," Mrs Arnott said.
They set up a Facebook page called "Josie's trade-up for oxytocin research".
"We wanted to do something different, so we wouldn't be asking for money," Mr Arnott said. "We started with a block of chocolate and we're aiming for bigger and better things."
The foundation would need US$1 million ($1.48 million) for the research, and had so far generated "just over half" according to Mr Arnott.
The foundation had already completed the first stage of their trials, and had two more to go.
"The first phase had promising results in combating the hunger and some of the other symptoms," Mrs Arnott said.
She was hopeful with the oxytocin treatment Josie may be able to live a normal life.
"That's the dream," she said.
They had already swapped the block of chocolate for two trailers of firewood, one from Good Neighbour and one from the Bethlehem Baptist Church.
Mr Arnott said they had received a "great response because it's a bit different".
"Plus she's cute," Mrs Arnott added.
The couple wanted to fundraise for the research so to be able to help other people with Prader Willi Syndrome.
"There are kids all the time growing up with this, most people haven't heard of it," Mrs Arnott said.
As of 5pm yesterday, the Facebook page had 217 likes.
They were looking for suggestions of what they should purchase to trade next. "Like an All Blacks jersey with signatures from the Rugby World Cup," Mr Arnott said.
Currently, sufferers of the syndrome were given growth hormone treatment, which was publicly funded for patients from 12 months old, and then after an additional six months of testing. Mrs and Mr Arnott were planning to pay for the growth hormone treatment earlier.
Can you help?
* To give a suggestion for what to trade, or for more information go to: www.Facebook.com/JosieTrade