Aussie Leo with growth hormone deficiency dreaming to star at World Cup like Messi

When bedtime comes in the Slattery household there is one book on the shelf father Liam returns to.

It's the story of Lionel Messi in the children's book series 'Little People, Big Dreams'.

Like his namesake, six-year-old Leo Slattery also has big dreams — but the two share more than a name.

"We used to read that story to our Leo. He got diagnosed with growth hormone deficiency when he was three," Liam Slattery told the ABC.

Leo's rare condition results from an insufficient production of growth hormone by the pituitary gland which boosts the growth of children, and helps adults maintain a normal body structure.

Paediatric Endocrinologist Peter Simm said treatment for children with the condition usually involves a nightly injections of synthetic growth hormone until the end of puberty.

He added a weekly dose of the treatment was also now available for patients.

"Then once they reach towards the end of growth, they get reassessed to see if they are still deficient in growth hormone," Dr Simm, from the Royal Children's Hospital in Melbourne, said.

"Then there has to be a decision about whether they need to be treated as adults because growth hormone has more effects than just on growth."

Two Leos, two treatment experiences

Mr Slattery and his wife Mia first began to have concerns about their son's growth when friends would ask whether their youngest son and Leo were twins.

The Brisbane-based couple were looking for answers about Leo's condition.

After several appointments with their local GP and referrals to paediatricians, and later an endocrinologist, they were getting closer to a diagnosis.

"When we first saw [the endocrinologist], she thought, 'he doesn't present like a child with that condition, but let's do all the tests anyway and rule it out for sure,'" he said.

"So even a doctor originally thought, 'I don't think this child does have it, but then run the test anyway', was so important.

Their experience stood in stark contrast to what his wife Mia was seeing in some of the US-based support groups she had joined online.

"Hearing stories of where they have to fight tooth and nail with insurance companies and doctors to try and get their child diagnosed," he said.

"In America, if insurance doesn't cover it, it's thousands and thousands of dollars."

According to the US National Library of Medicine, the average annual cost for Medicaid insured patients with growth hormone deficiency was $US18,069, and $US27,893 for commercially insured patients.

"I was looking at the box for one of his first treatments and it was $2,500 for the treatment," he said.

"We paid $60 because it was covered under PBS. So yeah, very thankful that we do have that system in Australia."

Messi's lifeline

Unlike Australia, the treatment of growth hormone deficiency is not subsidised by the government in Argentina.

It led a then 13-year-old Leo Messi to leave his boyhood club Newell's Old Boys in search of a place where he could get affordable access to his medication.

At the time, he asked his endocrinologist Diego Schwarzstein whether he would grow.

"You will be taller than Maradona," Dr Schwarzstein said.

In 2000, he found "the only club in the world that offered" to pay for his growth hormone deficiency treatment.

The agreement between the Messi family and Barcelona, which has now become folklore, involved a late-night dinner, a pen and a napkin repurposed as a contract.

After an impressive trial, Barcelona's then-sporting director Carles 'Charly' Rexach took no time to seal the deal he said would cement his legacy at the club.

The napkin was later sold at an auction for $US965,000

"It wasn't difficult for me to move to Barcelona because I knew I had to," Messi told Match of the Day magazine.

Victor Valdez, who grew up playing with Messi in Barcelona's academy, remembers those early days, saying it was not easy for him.

"Messi missed some training sessions because he felt dizzy after the injections. Some mornings, he could not come to school either, as he felt unwell," Valdez told the Athletic.

In the first two years at the club Messi broke his leg after playing in a friendly game with older players.

"It was a huge blow for him. We did not see him in Barcelona for a while after that — he went back to Argentina for some time," he said.

"It was all part of a tough process, and some people might not even be aware of that. But what Messi had to go through was far from easy."

Little Leo's football dreams

According to the Australian Pituitary Foundation, Messi's story is inspiring because it challenges assumptions about what people with growth hormone deficiency can achieve.

"One of the powerful things about Lionel Messi's story is that he had a specialist who saw potential, not just a condition," the peak advocacy organisation for pituitary patients and their families said.

"That's what every patient deserves — someone who helps them see a diagnosis as the start of a journey, not a limit on what they can do."

Six-year-old Leo Slattery, who has just started prep, is looking to join a football club to emulate his hero.

He is already working on his game, rushing over every Tuesday and Thursday to train with his nine-year-old next-door neighbour.

But until he can make his debut on the football pitch, he has been enjoying Argentina's journey at the World Cup.

He tuned in for the Argentina and England World Cup semifinal with his father beaming as they watched Messi save his country from elimination.

They watched the game on delay but they will be up bright and early to catch the final because little Leo does not want to miss his hero's final World Cup game.

"We were watching the game and I was like, 'Look at Leo Messi, look at how much shorter he is than everyone else — he's got what you've got," Mr Slattery said he told his son.

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