Isabella Leonard is one in a million - well almost. Just 28 people in Australia - and perhaps 300 in the world - are known to share her condition.

Isabella will be three years old in April, she lives in Coonamble and was diagnosed with the ultra rare Costello Syndrome when she was just nine months old.

With her family, she is helping doctors, specialists and researchers decipher what it means to live with Costello Syndrome.

Her mum Shawnee Towns, dad Stephen Leonard and seven siblings are learning more each day about the Costello Syndrome and helping Isabella find her way through the challenges it brings.

Isabella is a precious soon-to-be-three year old. PHOTO SUPPLIED.

Isabella is the middle child among her eldest brother Stephen who is 17 and Kobe, Destiny, Bratham, Chelsea, Willow and Tommy who is just five months old.

Her diagnosis came when, at nine months, she was the size of a two month old, could not gain weight and slept constantly which led doctors to finally seek genetic testing that confirmed her condition.

With so few children, or adults, with Costello Syndrome, the medical profession is on a constant learning curve and her parents have connected with other families via social media to share their thoughts and experiences.

"She's going really well," Shawnee said.

"There's a facebook group and we find out more about it (Costellos) from them than the doctors."

"Every year in the US they have a big get together where all the doctors, families and specialists get to meet and we wanted to host it in Sydney this year," she said

"There's me and three other mothers all working together to get it going."

Costello Syndrome is a genetic mutation that occurs just before birth, changing the DNA, and so far is impossible to predict or prevent.

Children with the condition are prone to cancers and tumours, heart problems, hip displacement and other orthopedic problems, difficulties with feeding, growth hormone deficiencies and blood glucose problems.

They also suffer from issues with brain and muscle development, malformations and spinal cord complications.

For Isabella, as well as developmental delays and some obvious physical problems, there are many hidden risks that need to be constantly monitored for signs.

"She's had three-monthly ultrasounds and MRIs of her spinal cord, but so far so good," Shawnee said.

"She already has a heart murmur, and that's what helped them pick up that she had Costellos."

Shawnee is just 26 and is learning on the run while dealing with the travel to Dubbo for regular appointments, discussions with multiple specialists and with more to come, including trips to Sydney.

"We got a break over the holidays but so far we've been going four times every six months," she said.

"Emma Horan, who is an OT (occupational therapist) is working with her at the moment so we don't have to go as much."

Shawnee says that having Emma in town has made a big difference for Isabella and her family.

"It's good because Coonamble didn't really have anything much in speech and OT and they have everything now," she said.

"Isabella doesn't like big crowds but since Emma's been coming around she's got heaps more social. She really connects with her - it was a big relief."

Costello Syndrome was only discovered in 1970 and a short life expectancy is part of the condition but Shawnee says that the oldest living Costello man is 42 years old.

"That gives us a lot of hope," she said.

There is a lot of uncertainty about what is to come for Isabella but having a loving family and parents determined to do their best helps Isabella find her way.

"It's a scary thing to live with," said Shawnee.

"But she's already proven a lot of the doctors wrong. She's not meant to walk till she's five and she's already walking."

"Isabella's favourite things to do is to listen to country music, ride her little trike bike and eat banana custard," she said.

"The other kids love her. They miss out on some stuff because of her but they really look after her."

COVID has prevented many of the awareness raising activities planned for Costello Awareness Day but Isabella's family are still working to connect her with other Costello sufferers.

It now looks like the big Costello gathering they're working on will not be held until 2023.

Last Thursday 27 January was international Costello Syndrome Awareness Day. To find out more go to www.costellosyndromeusa.org.