The Bright Side of a Genetic Disease
Mothers of hemophiliacs have lower death rate
(HealthDay is the new name for HealthScoutNews.)
THURSDAY, July 31, 2003 (HealthDayNews) -- Having two genes for hemophilia may be bad news, but carrying just one causes a remarkable reduction in the risk of death from heart disease and in overall mortality, a Dutch study finds.
The death rate from artery-blocking heart disease was 36 percent lower in women who carried just one gene for the blood disease than for women without a hemophilia gene. And their overall death rate was 22 percent lower, says a report in the Aug. 2 issue of The Lancet on a study of more than 1,000 women.
Hemophilia reduces the ability of the blood to clot, and the males who have it can suffer periodic bleeding crises. With rare exceptions, it occurs only in males, because the genes for the proteins that govern blood clotting are on the X chromosome.
Women have two X chromosomes, but males have only one. So when a woman inherits one X chromosome that lacks a clotting gene, the defect is almost always overcome by the other, normal chromosome. There is no comparable gene to overcome the lack on the smaller Y chromosome found in men.
Hemophilia is relatively rare. An estimated 20,000 Americans have it, and about 400 boy babies with the condition are born each year in this country. The Dutch researchers were able to track down 1,012 mothers of hemophilia patients in that country; the women were born between 1961 and 1968.
Public health records listed 261 deaths among those women up to November 2000, when the study ended -- 22 percent less than the death rate for the general population, the researchers report. There were 39 deaths from ischemic heart disease, the kind that occurs when a clot blocks an artery.
"We found that even a mild decrease in coagulability causes a quite remarkable decrease in mortality," says Dr. Alexandr Sramek, an epidemiologist at Leiden University Medical Center and co-author of the report.
The decrease in cardiovascular deaths doesn't explain the overall drop in mortality, Sramek says, so he and his colleagues speculate a bit. The women in the study all were mothers, and there is some data indicating that women who don't bear children are at lower overall risk.
It could be that having a child with hemophilia might lead women to refrain from future pregnancies, which pose a health risk. Or the presence of a severe hereditary disease in the family could promote health-conscious behavior within the family.
Unlikely, Sramek says: The study found no differences in lifestyle between the women who bore hemophiliac boys and those who didn't.
The real message of the study seems to be for cardiologists, says Dr. F. R. Rosendaal, another member of the research team.
"This finding re-emphasizes the role of clotting and changes in clotting in the development of myocardial infarction [heart attack], which may in the future have implications for prevention of this disease," Sramek's prepared statement says.