"Hemophilia is an genetic bleeding disorder, affecting mostly males, that prevents blood from forming an effective clot" (qtd. in "Hemophilia Encyclopedia"). Hemophilia comes from the Latin word hemo, meaning blood, and philia meaning love. Blood in a person that does not have hemophilia contains proteins that act as clotting factors to stop bleeding. Hemophiliacs are either missing these clotting factors or the clotting factors are not working properly ("Hemophilia - a Timeline"). .
There are three different levels of severity of hemophilia: mild, moderate, and severe ("Hemophilia - a Timeline"). The level of severity corresponds with the amount of clotting factor present in the blood ("Hemophilia"). The level of severity a hemophiliac is born with does not change with time, i.e., a person born with a moderate case of hemophilia will not develop severe hemophilia ("Hemophilia Encyclopedia"). .
There are two types of hemophilia: hemophilia A and hemophilia B. Persons with hemophilia A have a factor VIII deficiency, and persons with hemophilia B have factor IX deficiency. People are much more likely to have hemophilia A than hemophilia B. Because it is the most common of the factor deficiencies, hemophilia A is also known as "Classical hemophilia" ("Hemophilia Encyclopedia"). .
The gene for hemophilia is found on the X chromosome. Women are carriers of the disease. "A carrier is a person who has a defective gene for a certain trait, such as hemophilia, but who does not exhibit that trait" (qtd. in "Hemophilia Encyclopedia"). Males have one X chromosome and one Y chromosome, while females have two X chromosomes. In this fact lies the reason why hemophilia in women is rare. While one of the X chromosome in a female may contain a nonfunctional clotting factor gene, her other X chromosome will usually compensate for the lack of or nonfunctionality of the clotting factor. Males, on the other hand, have only one X chromosome.
"Hemophilia ni ugonjwa wa kutokwa na damu wa urithi, unaowasumbua wanaume hasa, ambao huzuia damu isifanyize nguzo yenye matokeo" (qtd. katika "Hemophilia Encyclopedia"). Neno hemophilia linatokana na neno la Kilatini hemo, linalomaanisha damu, na philia linalomaanisha upendo. Damu ya mtu asiye na ugonjwa wa kuvuja damu ina protini ambazo hufanya kazi kama sababu za kuganda damu ili kuzuia kutokwa na damu. "Hemophilia ni ugonjwa wa ""kuchanganyikiwa kwa damu"" ambapo kuna sababu za kuganda kwa damu ambazo hazifanyi kazi vizuri, na kwa hivyo hazifanyi kazi vizuri." . Kuna viwango vitatu tofauti vya ukali wa ugonjwa wa kuvuja damu: upole, wa kadiri, na mbaya ("Hemophilia - a Timeline"). Kiwango cha ukali kinalingana na kiasi cha kichocheo cha kuganda kilichopo katika damu ("Hemophilia"). Kiwango cha ugonjwa wa hemophilia kinabadilika wakati wa kuzaliwa, kwa mfano, mtu aliyezaliwa na ugonjwa wa hemophilia wa kiwango cha kati hatapata ugonjwa wa hemophilia kali. . Kuna aina mbili za ugonjwa wa kutojua damu: ugonjwa wa kutojua damu A na ugonjwa wa kutojua damu B. Watu wenye hemophilia A wana upungufu wa sababu ya VIII, na watu wenye hemophilia B wana upungufu wa sababu ya IX. Watu wana uwezekano mkubwa zaidi wa kuwa na ugonjwa wa hemophilia A kuliko ugonjwa wa hemophilia B. Kwa sababu ni ya kawaida zaidi ya upungufu wa sababu, hemophilia A pia inajulikana kama "Classical hemophilia" ("Hemophilia Encyclopedia"). . Jeni ya hemophilia hupatikana kwenye kromosomu ya X. Wanawake ni wabebaji wa ugonjwa huo. "Mchukizaji ni mtu ambaye ana jeni lisilofaa kwa ajili ya tabia fulani, kama vile hemophilia, lakini ambaye haonyeshi tabia hiyo" (qtd. katika "Hemophilia Encyclopedia"). Wanaume wana kromosomu moja ya X na kromosomu moja ya Y, huku wanawake wakiwa na kromosomu mbili za X. Jambo hilo ndilo linalosababisha hemophilia kuwa nadra kwa wanawake. Wakati moja ya X chromosome katika mwanamke inaweza kuwa na nonfunctional coagulation factor jeni, yake nyingine X chromosome kawaida italipa kwa ukosefu wa au nonfunctionality ya coagulation factor. Kwa upande mwingine, wanaume wana kromosomu moja tu ya X.