Born with a rare condition that made her bones “soft”, restricted her growth and set her up for a life of pain and health complications, the five-year-old has become the first Victorian child offered the chance at a new wonder drug promising a bright future.

Five months after undergoing extensive surgery to straighten the bending bones of her legs, Kiah last week had her first injection of Crysvita — an almost $10,000-a-fortnight treatment to overcome the one in 20,000 genetic condition X-linked hypophosphatemic rickets.

“We are so privileged,” Kiah’s mother, Amber Williams, said.

“I’m pretty certain she is going to be like a normal child.

“We are hoping that when she normalises and looks like everyone else, she will grow the way she is meant to grow.

“She will live quite normally and it will be a very invisible condition.

“We are hoping we can get her running, skipping, walking and building up her muscles after surgery. She basically needs to learn to walk again with new legs.”

More than a dozen other Royal Children’s Hospital patients suffering XLH will also receive the life-changing drug.

Kiah showed no interest in walking until her second birthday and, when she finally did, her gait was more of a “waddle”.

Worse, her leg bones began to buckle, triggering a search for answers that was finally resolved 18 months later through DNA testing.

The condition meant Kiah would have soft bones that might require constant surgery to repair, as well as complications including stunted growth, hearing and teeth loss, skull deformities — and pain.

“If it is all you know, you grow to get used to it,” Ms Williams said.

“But, it did prevent her from jumping on hard surfaces because it grinds, walking long distances was hard for her, walking up and down stairs is hard for her.

“But she has an amazing attitude.

“Kiah is really inspiring. She doesn’t complain, she just knows that is the way it is and copes with it.”

Caused by an inability of her kidneys to pass bone-strengthening phosphate to her body, Kiah had a strict regimen of seven medications a day to limit the damage.

But when she began ballet classes the emotional pain became just as raw.

“When she was in her class, that is when she realised she was different,” Ms Williams said.

“She couldn’t keep up with the other students and would tag along. That was really sad for her.

“I did a lot of work with her and she got to a point where she loved her bowlegs, but we took her out of ballet because it was not OK for her to be there anymore.”

Kiah did not respond well to existing phosphate and calcitriol treatments, but her parents and RCH specialists were closely monitoring US trials of a protein called FGF23.

After passing trials with stunning success, the treatment has been commercialised, approved and subsidised for use as Crysvita in the US and UK over the past two years.

While any Australian subsidisation is still to be decided, RCH endocrinologist Professor Margaret Zacharin said securing an agreement to offer the medication to Kiah and other patients could mean the world.

“This is the first time we have been able to treat the disease, not its consequences,” Prof Zacharin said.

“There is a massive difference (with previous treatments). There is a difference in linear growth, there is a difference in improvement in leg bowing and rickets, and there is a difference in the health of the patient.

“This has the capacity to properly heal the bones. It may not end up being absolutely perfect, it is too early to say.”

Although she will need injections every fortnight, the treatment is expected to heal past damage to Kiah’s bones as well as prevent further consequences.