Symphonya Turua sits silently in her custom-built supportive frame as her three siblings laugh and play around her.

The 3-year-old tot can't join in but the expressions that spread across her face indicate she's taking in all the action and activity.

Symphonya was born with a rare condition called lissencephaly, or smooth brain.

Her brain has no folds and was caused by nerve cells not moving to their permanent locations during the early stages of pregnancy.

The Avondale youngster can't walk, talk or sit up, and requires round-the-clock care.

Mum Lesina Turua, 35, says learning of her daughter's condition was "devastating".

"I thought maybe I had done something during the pregnancy - I was very emotional," she says.

"But it wasn't a genetic trait, just something random that happened."

Symphonya's one of about 20 Kiwi children with smooth brain and upon her diagnosis, Turua and her husband Karika struggled with the lack of support and information available locally.

They took to communicating with other families, some from overseas, via social media sites like Facebook.

The pair hope to start up New Zealand's first support group where other families affected by the condition can communicate and offer advice.

"It will be a place for parents to vent, support each other and share what works and doesn't work for them," Turua says.

"They might be doing something that we haven't tried and that would be really beneficial for Symphonya."

Specialists initially said Symphonya would live to be about two years old but medication and advanced equipment has increased her life span to about 10 years, Turua says.

Symphonya is fed liquids and daily medication through a feeding tube and requires regular speech language, physio and occupational therapy.

Attending special needs daycare Homai is one of her favourite activities.

The Turuas are taking each day as it comes and are enjoying every moment spent with Symphonya.

"She's already defied the odds and at the end of the day we're huge believers in just simply loving our kids," Turua says.

"It makes a big difference to their quality of life."