A Montreal man who has lived with an undiagnosed condition for more than 30 years finally has an answer to what is wrong with him, thanks to the wonder of modern genetic research.

Steven Francis, 35, has been ill almost his whole life. Since the age of six months, he has been unusually susceptible to viral, fungal and bacterial infections of all kinds.

He’s developed respiratory infections, kidney problems, blood infections, colon infections, and shingles. Twice, his illnesses have left him near death.

Doctors suspected Francis must have a genetic disorder that left him at the mercy of infections, but despite running test after test, they couldn’t diagnose what was wrong with him.

Then in 2012, Francis went to the Research Institute of the McGill University Health Centre to see infectious diseases specialist Dr. Donald Vinh, who sees himself as a sort of medical detective. Vinh says he was happy to try to crack Francis’ case.

“He had not only been investigated here for 30 years but also in Toronto and in the United States and they hadn't come up with anything. But we took that as a challenge,” Vinh recalls.

Vinh suspected Francis had a genetic problem with his immune system, but one that was rare enough to be considered an orphan disease, meaning a disease that affects fewer than one in 2,000 people and is not well studied.

He reviewed all of Francis’ years of test results and looked at his family history, checking whether he had been tested for any of the many genetic conditions that have been identified in recent years.

Vinh discovered Steven had a faulty ZAP70 gene, which is critical for the proper function of the immune system. The gene serves to synthesize a protein of the same name that helps activate our immune system’s killer T-cells. Without the ZAP70 protein, the body can't defend itself effectively against most infections.

Most who have a mutation on the gene die young, usually before the age of five, but doctors are learning that some can live into adulthood.

Francis says it was a huge relief just to put a name to his condition.

“I was really ecstatic, really happy that finally they found something after so many years,” he says.

The only treatment for the condition would be a bone marrow transplant, but that procedure needs to be performed before the age of five. So Vinh set to work to find a therapy that might still offer help to Francis.

Through Francis, Vinh and his team were able to learn exactly where to find the ZAP70 mutation and how it behaves. They then moved on to developing a molecule that they believe could block the gene mutation.

Earlier this year, the team published a paper detailing their research. Now, they want to begin human testing of the molecular therapy. What's needed now is a pharmaceutical company to invest in developing the treatment so they can offer it to Francis.

Only then will Vinh consider this medical mystery case closed.

With a report from CTV Montreal’s Cindy Sherwin