A small cut that will not stop bleeding can signal a clotting disorder. Hemophilia is an inherited condition in which blood fails to clot normally because of deficiency in a specific clotting factor. The two most common forms are hemophilia A (factor VIII deficiency) and hemophilia B (factor IX deficiency).

Both are X-linked recessive. Males who inherit a mutant allele on their single X chromosome are affected; females are usually carriers. Severity correlates with residual factor activity. Spontaneous joint and muscle bleeds are characteristic of severe disease.

Treatment consists of intravenous replacement of the missing factor, either on demand or prophylactically. Extended half-life products and, more recently, gene therapy have improved management. Early diagnosis and comprehensive care prevent long-term joint damage and allow active lives.

• Inherited clotting-factor deficiency
• Usually X-linked recessive
• Causes prolonged bleeding
• Treated with factor replacement or gene therapy