A hemopheliac is someone with a bleeding disorder resulting from any missing clotting factors in their blood. Vasoconstriction isn't generally the problem in hemophiliacs, nor is it the destruction of pathogens. If fibrin threads are not present to help form the platelet plug, then excessive bleeding occurs. Fibrin is one clotting factor that a hemophiliac may be missing which is then causing the disorder.
I believe the answer is a mutation.
Answer:
Haemoglobin (Hb) is a protein present in red blood cells that transports oxygen and gives blood its dark/vivid red color. The amount of haemoglobin in the blood varies from person to person. Men's levels are often greater than women's. This is scientifically proven however, it is often but not all the time.