Doctors at the MUHC have solved the mystery of a rare undiagnosed condition.

South Shore man Steven Francis has lived with the genetic condition for more than 30 years – his whole life – with it.

From the age of six months old, every three to four months, Francis gets sick: Sinus, fungal and blood infections, inflammations of the colon, shingles, respiratory problems, kidney problems.

“Symptom by symptom, year by year,” he said.

He was near death twice, but his rare disorder couldn't be diagnosed until he went to see MUHC infectious diseases specialist Dr. Donald Vinh.

Vinh relishes his role as a sort of medical detective.

“Can we do something that can help the patient care? Can we identify what their problem is? Can we fix their problem? We're driven by those questions,” he said.

Rare or orphan diseases affect fewer than one in 200,000 people.

Vinh suspected Francis had a genetic problem with his immune system.

“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,” he said.

They discovered Francis has a faulty gene that won't produce enough of a certain protein, called ZAP70. It means his immune system won't fight off infections and sometimes turns on itself.

The mutation is known to be fatal without a bone marrow transplant before the age of 5. Doctors now know it's found in adults as well.

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

Unlocking that secret wasn't enough, however.

“How can we fix what's broken?” said Vinh. “So we developed a molecule that targets specifically his mutation and prevents it from doing its thing while allowing the normal gene to function properly.”

The treatment could help patients with other immune problems as well, though a pharmaceutical company will be required to invest in that treatment.

Vinh, though, considers the case closed.