Discovery Leads to Hemophilia A Test

Geneticists on Sunday reported that they have solved a key mystery about hemophilia and developed a new test for telling women whether they risk bearing sons with the disease.

The test should give a definitive answer in about 45% of families affected by severe cases of hemophilia A, the most common form of the blood disorder, researchers said.

Hemophilia A appears in about one in every 5,000 males, and about half the cases are considered severe. The disease is caused by defects in the gene that tells the body how to make factor VIII, a substance that promotes clotting.

People with severe hemophilia may have to inject themselves with factor VIII 30 to 50 times a year to control internal bleeding and maintain health.

Scientists had been puzzled by the fact that in about half of the severe cases, they were unable to find any defect in the factor VIII gene. The new study shows that the problem is an unusual flaw, apparently caused by a process not described before in any disease, said study co-author Jane Gitschier of UC San Francisco and the Howard Hughes Medical Institute.

Gitschier presents the new work in the November issue of Nature Genetics with colleagues at her university, the Johns Hopkins University School of Medicine in Baltimore and the University of Geneva Medical School in Switzerland.

Women can have the defective gene without getting hemophilia because they also have a second factor VIII gene. Males have no such backup.