Hemophilia, a rare inherited bleeding disorder in which blood doesn't clot normally - meaning any cut can be deadly - is a lot less rare than previously estimated. 

A new paper states that as many as 1,125,000 men around the world have it, 418,000 with a severe version of the mostly undiagnosed disease, which is 3X greater than the 400,000 people previously estimated.

Hemophilia is caused by a defect in the F8 or F9 gene which encodes instructions for making the factor proteins that helps blood clot. For those with hemophilia, lack of treatment leads to chronic and disabling joint disease, while bleeding into organs and brain hemorrhages can lead to disability and death. It is found almost exclusively in men and is currently treated with infusions of factor to prevent or stop debilitating bleeds, but treatment is expensive and scarce in many countries.

Dr. Alfonso Iorio (right). Credit: McMaster University

There are two main types of hemophilia: Hemophilia A has the factor 8 (F8) gene defect, and hemophilia B has a factor 9 (F9) gene defect. The new analysis found that per 100,000 males, 21 will have hemophilia A or B, seven of whom severely; among newborns, per 100,000 males, 29 will have hemophilia A or B, of whom 12 will have the severe form of disease. 

Putting the numbers together, the 'life expectancy disadvantage' associated with hemophilia may be estimated and varies depending with the availability of care. For those born with hemophilia, the chances of living a life of normal duration and quality will be reduced by 64% in upper-middle income countries, 77% in middle income and up to 93% in low income countries.

"This paper is a milestone in our journey to providing care for hemophilia patients worldwide," said McMaster University Professor Alfonso Iorio, lead author of the paper. "Knowing how many patients are expected in each country given its population is an important measure of the efficiency of the health care system. Knowing how many patients should be there, and how many less instead are reported to national and international registries is a measure of the work left to be done."