But his mum is afraid the six-year-old who has had 13 surgeries will one day lose the treatment giving him the will to smile and ability to live.

Beau used to spend every day in such pain he could not walk up stairs or play for more than 15 minutes. People with his rare condition, Morquio A, live an average of 25 years.

Beau's family is one of several calling for the only available treatment for Morquio A, Vimizim, to be funded via the government scheme Life Saving Drugs Program.

It is the second attempt for the treatment to be subsidised, after an application for it to be placed on the Pharmaceutical Benefits Scheme was rejected last year.

Beau is currently on a trial for Vimizim through a pharmaceutical company. The funding for the therapy was discussed in federal parliament this week.

Beau's mother, Samantha, says that since being placed on the trial, Beau can run, attend school with his brothers and "be a normal kid".

"His life was pretty much gone when he was diagnosed at one year old," Ms Cosgrove said.

"When we got the phone call two years later to say he was on the trial, I was on the way to the beach and I cried for two days. We finally thought he could have a future."

Morquio A affects just 21 Australians, impacting the development of their bones, respiratory system, eyesight, hearing, teeth, liver and other body parts. People with the disease are missing - or don't make enough of - an enzyme that allows their body to break down certain materials.

Even for those currently receiving treatment, via the manufacturer, until Vimizim is funded by the federal government, there can be no guarantees of continued access.

Every week Beau travels to Canberra from Taralga, north of Goulburn, for treatment. But he could be cut off from the lifeline if the federal government again refuses to fund it.

"I'm afraid that the drug company may have had enough of waiting on the government and pull the drug," Ms Cosgrove said. "That terrifies me."

Despite Beau's battle with uncertainty, Ms Cosgrove said he is one of the lucky ones with Morquio A. As he was diagnosed before the drug became available in Australia, he was eligible for the trial. But he has a friend with the same condition who is "living a completely different life" because he can't access the expensive drug.

The Pharmaceutical Benefits Advisory Committee considered a submission to fund Vimizim in 2016. But the committee did not find it cost effective enough for the Pharmaceutical Benefits Scheme.

Executive Officer of Rare Voices Australia, Nicole Millis, said the decision was devastating for families and unfair given it was found to be clinically effective.

"At the moment these patients are receiving treatment via compassionate funding, but without government funding there is no certainty that the compassionate funding will continue," Ms Millis said.

"It is a small patient group but they are brave fighters, they've done everything right in this process and the system has just let them down. There is a way for it to be treated and yet they are left having to fight for that right."

During senate estimates in parliament this week, the federal health department said it was considering the reimbursement of Vimizim on the Life Saving Drugs Program.

The questioning came in the wake of new research published in the Australian Health Review journal, which urged the federal government to urgently reassess how it funds treatments for ultra-rare diseases.