Hemophilia is a sex-linked hereditary blood coagulation disorder. The blood's inability to clot results in excessive bleeding, even from slight injuries. The disease is caused by a lack of blood proteins, called factors, which participate in blood clotting.
There are three types of hemophilia; hemophilia A, B and C. Hemophilia A is the most common form of the disease and is found in 80 percent of all hemophiliacs. It is caused by a lack of factor VIII. The second most common form is hemophilia B, which is caused by the absence of factor IX. Twenty percent of the people with this disease have hemophilia B. Hemophilia C is caused by the lack of factor XI and only a small percentage of the people with the disease have this. The gene for hemophilia is located on the X chromosome. Hemophilia is a recessive sex-linked trait.
Males more commonly get hemophilia because they only need to inherit one bad X chromosome, whereas women need to inherit two.
Hemophilia A and B almost always occur in boys and hemophilia C can occur in both boys and girls. One in 10,000 men have hemophilia A or B. The disease is passed from mother to son through one of the mother's genes. Most females who have the defective gene are only carriers and show no signs of the disease.
Of the children of a female carrier and a normal male, one half of the boys will have hemophilia and half of the girls will be carriers. Of the children of a normal female and a male hemophiliac, all of the boys will be normal and half of the girls will be carriers. Of the children of a hemophiliac female and a normal male, all of the boys will have hemophilia and all of the...