David Hartzell age 15, of Orlando, Fla., for his question:

WHAT CAUSES HEMOPHILIA?

Hemophilia is a group of diseases character:zed by an abnormal tendency to bleed profusely from the slightest wound. The diseases are caused by an insufficiency or absence of certain blood proteins, called factors, that participate in the complex chemical reactions involved in blood clotting.

The most common form, hemophilia A, is observed in 80 percent of hemophilia patients and derives from a lack of blood factor VII. 1n the second most common, hemophilia B, factor 1X as missing.

The severity of hemophilia varies greatly. The bleeding may occur spontaneously, following severe exertion, or as a result of a simple cut.

Hemorrhaging into joints and muscles can be disabling. Before the advent of modern therapy, the chance of survival to adulthood was poor.

The application of globulin or fibrin foam may help coagulation in local hemorrhages. Freshly frozen blood plasma is used to treat some mild forms of the disease.