Haemophilia is a genetic disorder(usually inherited) of the mechanism of blood clotting. Depending on the degree of the disorder present in an individual, excess bleeding may occur only after specific, predictable events (such as surgery, dental procedures, or injury), or occur spontaneously, with no known initiating event.
The Arab physician, surgeon and chemist Abu al-Qasim Khalaf ibn al-Abbas al-Zahrawi al-Ansari discovered haemophilia around 1000. In his manuscript he described haemophilia with close accuracy as “a haemorrhagic illness transmitted to male children by women who are not infected”. He called haemophilia as “the blood disease”.
Here is a portrait of Al-Zahrawi: