Hemophilia is a type of hereditary bleeding disorder. Different types of hemophilia are caused by mutations in the genes for blood clotting factors, leading to a clotting disorder. The X-linked bleeding disorders primarily affect males, although in extremely rare cases they can appear in females. The severity of each type is variable, and treatments are available. PubMed Health Wikipedia
- Factor VIII deficiency causes an X-linked disorder known as hemophilia A. This is the most common type of hemophilia.
- Factor IX deficiency, also known as Hereditary factor IX deficiency disease, causes an X-linked disorder known as hemophilia B. A research study using gene therapy has apparently cured four patients who no longer require injections of factor IX.   
- Factor XI deficiency causes the rarer, milder disorder known as hemophilia C. It can affect either males or females and is more common in Ashkenazi Jews.
The word hemophilia (also spelled haemophilia) comes from the Greek haima, meaning "blood," and philia, meaning "to love."