Both haemophilia A and haemophilia B are characterised by the delayed and ineffective production of blood clots, which results in prolonged bleeding and spontaneous internal bleeding.

Haemophilia A is more prevalent than haemophilia B, affecting one in every 5,000 males versus one in every 40,000 males.

Both haemophilia A and B are disorders caused by X-chromosome gene abnormalities (X-linked disorders). Queen Victoria carried the haemophilia A gene.

Both haemophilia A and B are recessive disorders, meaning that two defective copies of the gene are required for symptoms to manifest (with just one mutated copy they are a carrier).

Due to the location of the defective gene on the X chromosome, males are significantly more likely to be affected than females, as males only have one X chromosome.

The disease genes are located near together on the X chromosome and have the designations F8 and F9. A mutation of the F8 gene causes haemophilia A, whereas a mutation of the F9 gene causes haemophilia B.

What proteins do the F8 and F9 genes encode Eighth and ninth factors, respectively. Both Factor VIII and Factor IX are coagulation factors that play crucial roles in the blood clotting process.

In situations of severe haemophilia, a mutation in either the F8 or F9 gene can result in aberrant or diminished quantities of Factor VIII and Factor IX, and their action can be abolished entirely.

Without these components, the blood clotting process is less effective and blood clots cannot properly form in response to damage. Consequentially, uncontrollable, persistent bleeding ensues, leading to substantial blood loss.

Bleeding, haemorrhaging, and bruising are readily identifiable signs of haemophilia.

Haemophilia A and B share symptoms that can range from moderate to severe, depending on the extent to which Factor VIII and IX levels are impaired.

Patients with haemophilia frequently require significantly more time to recover from injury or surgery. Internal bleeding caused by delayed clotting might result in joint swelling and pain.

Physicians can establish whether a patient has haemophilia A or B by observing whether giving Factor VIII or IX alleviates symptoms.

If Factor VIII alleviates disease symptoms, the patient has haemophilia A; if Factor IX does, the patient has haemophilia B.

Additionally, genetic testing can be done to determine if the F8 or F9 gene is mutated and, thus, whether the individual has haemophilia A or B.

Haemophilia A or B are treated with regular injections of Factor VIII or Factor IX into the blood. In cases where bleeding is possible, such as during surgery, an additional injection of clotting factors may be required.

Gene therapy is being studied as a possible therapeutic alternative.

In a study conducted at University College London, haemophilia B patients were injected with a virus containing a portion of DNA holding the instructions for generating normal Factor IX. During the 16-month trial, the levels of Factor IX in the blood of those treated with the virus increased. Consequently, some of the patients no longer required routine Factor IX injections.

This approach will need to be tested on a significantly larger number of patients before its advantages and hazards can be accurately evaluated.