Hemophilia A
Hemophilia A is the most common type of hemophilia. It is also known as factor VIII deficiency or classic hemophilia.
It is largely an inherited disorder in which one of the proteins needed to form blood clots is missing or reduced. The disorder is caused by an inherited X-linked recessive trait with the defective gene located on the X chromosome. Females have two copies of the X chromosome. So if the factor VIII gene on one chromosome doesn't work, the gene on the other chromosome can do the job of making enough factor VIII. Males, however, have only one X chromosome, so if the factor VIII gene on that chromosome is defective, they will have hemophilia A.