For a child to get Tay-Sachs both parents need to be carriers of a genetic mutation that causes the disease. If both parents are carriers, a child has a 25 per cent chance of developing the disease.
The National Health Service in England estimates only about one in every 360,000 children born worldwide has Tay-Sachs.
Ms Hooper, originally from Martinborough and Mr Stephen, who now live in Stokes Valley, received the diagnosis in July that Violet had Tay-Sachs.
"Violet was developing completely normal, everything was perfectly fine up until seven months and then she started to regress.
"She [now] doesn't have arm and leg control, she can't grasp things or hold anything, she can't sit up on her own or roll over, or stand or anything like that, she's got no control.
"She can make some noises and laugh but even that will go and as things progress she'll do less and less."
When Violet was 11 months old Ms Hooper took her to the doctor, to have tests done, and the family were told Violet had Tay-Sachs.
"It took a while for it to sink in, it was definitely not very nice. It would be great if there was some magic cure that just happened but we've got to be realistic, they haven't found one yet.
"Generally the life expectancy is between three and five years old. It's not long."
The couple had never heard of the disease before Violet's diagnosis and Ms Hooper has another child, 10-year-old Zakary, who does not have Tay-Sachs.
The disease is thought to be most prevalent in those of Eastern-European Jewish decent, and also French Canadian and Irish-American decent. Ms Hooper and her partner both have Irish ancestors.
The couple have tried, unsuccessfully, to find other children with Tay-Sachs in New Zealand.
"Currently she's the only case in New Zealand, we've been able to get hold of someone who had a child that passed away in 2008, that's the only recent case that we've heard of and that was down south.
"We're part of a Facebook group with other parents with children with Tay-Sachs but they are all overseas.."
Ms Hooper said apart from having Tay-Sachs, Violet was a happy and healthy baby.
"Most of the time she's pretty happy, she doesn't complain unless something is actually wrong, even when she's sick she just sleeps.
"She's a great little girl."
The couple want to raise money for a special chair that Violet will be able to sit upright in, called a P Pod. "P Pod is something a couple of the people I've talked to through Facebook got for their kids, it's like a bean bag with a moulded seat because she can't sit up on her own, she doesn't want to just lay there.
"She sits in a normal bean bag at the moment."
They also want to raise awareness of the disease, which people can be tested for.
