Canadian scientists have discovered the genetic cause for a peculiar bleeding disorder that can be traced back to a single family in Quebec.

People with the condition, known as Quebec Platelet Disorder, have platelets in their blood that, instead of clotting to stop bleeding, actually become clot busters and promote bleeding.

People with the disorder can find that a cut can bleed for days, or an ordinary bruise can balloon into the size of an orange. In serious cases, hundreds of blood transfusions are required for recovery.

But now, the genetic cause of QPD has been discovered.

A team led by hematologist Dr. Catherine Hayward at McMaster University in Hamilton, Ont. has discovered the disorder is caused by a mutation involving an extra copy of the uPA (urokinase plasminogen activator) gene.

The mutation causes overproduction of an enzyme that accelerates blood clot breakdown.

What's more, Hayward's team has also been able to develop a genetic test for the condition.

That genetic test has already been put to work. A recent newborn of the Quebec family most impacted by the condition was able to have a test right after his birth to discover whether he had the condition.

The test should also be able to ascertain how many people have QPD. At present, it's estimated that one out of 150,000 persons has QPD in some parts of Canada. But Hayward and fellow researchers believe the true prevalence of the condition has likely been underestimated.

Hayward says QPD is the first bleeding problem attributed to a mutation in the uPA gene. It's also the first bleeding disorder attributed to having an extra copy of a gene, rather than a defective copy.

Hayward says that now that researchers know the mutation, they can focus on solving why there is tremendous uPA overproduction in QPD platelets."

Because the genetic cause of most bleeding disorders continues to be a mystery,

"it's satisfying to know that our team tackled the genetic cause of a really fascinating genetic disorder and have an answer," she said in a news release.

"And, it's not the answer anybody expected, which makes it even more interesting."