Gabrielle Jones is barely four years old and she’s already saved a life.

And, while that’s remarkable enough on its own, making it even more special is the fact that the life she saved was of her baby brother Avery.

Last year, Avery came down with a fever that wouldn’t go away. The Meadowvale boy’s parents, mother Michelle and father Stefan, took him to the hospital on several occasions and to a pediatric clinic. But, despite antibiotics being prescribed, the fever just wasn’t breaking.

They returned to Credit Valley Hospital and their then four-month-old son underwent a battery of tests, including blood work. Not liking what they saw in the results, the CVH doctors referred him to the Hospital for Sick Children in Toronto.

There, physicians diagnosed Avery with hemophagocytic lymphohistiocytosis (HLH). According to the Johns Hopkins Medicine website, the life-threatening and rare condition has certain white blood cells of the immune system malfunctioning and that causes them to attack and damage the body’s other blood cells.

“I had never heard of it,” admitted Stefan. “Everyone knows about cancer or leukemia but HLH? Once we found out, we spent days doing research to try and learn as much as we could about something we had never heard of.”

It was a scary time for the family. Stefan and Michelle learned they both carried the gene that caused HLH and that meant their offspring had a one in four chance of being diagnosed with it. They had to take their other children — Gabrielle as well as Sienna, 8, and Aiden, 5 — for testing to see if they had the condition. Thankfully, they didn’t.

Steroids and chemotherapy would serve as a temporary treatment for Avery’s HLH, the family said. But, the only way to cure it was a bone-marrow transplant.

The parents were told that they should get tested, along with Avery’s siblings, to see if they were a match for donation. It’s highly unlikely that the extended family would be, which narrowed down the field of prospective donors, and they were informed that less than 25 per cent of the time a donor is found in the immediate family.

Last year in June, memorably enough on Michelle’s birthday, she received two phone calls that would prove to be the best gift she could have hoped for.