Haemophilia A and haemophilia B are inherited severe bleeding disorders. Haemophilia A is caused by a deficiency in factor VIII. Haemophilia B (also known as Christmas disease) is caused by a deficiency in factor IX.
X Linked Recessive
Both haemophilia A and B are X linked recessive. This means in order to have the condition all of the X chromosomes need to have the abnormal gene. Men only require one abnormal copy as they only have one X chromosome. Women require abnormal copies on both their X chromosomes, and if only one copy is affected they are a carrier of the condition.
Therefore haemophilia A and B almost exclusively affect males. For a female to be affected they would require an affected father and a mother that is either a carrier or also affected.
Signs and Symptoms
Both haemophilia A and B are severe bleeding disorders. Patients can bleed excessively in response to minor trauma and are also at risk of spontaneous haemorrhage without any trauma.
Most cases present in neonates or early childhood. It can present with intracranial haemorrhage, haematomas and cord bleeding in neonates.
Spontaneous bleeding into joints (haemoathrosis) and muscles are a classic feature of severe haemophilia and worth remembering for your exams. If untreated this can lead to joint damage and deformity.
Abnormal bleeding can occur in other areas:
- Gastrointestinal tract
- Urinary tract causing haematuria
- Retroperitoneal space
- Following procedures
Diagnosis is based on bleeding scores, coagulation factor assays and genetic testing.
Management should be coordinated by a specialist.
The affected clotting factors (VIII or IX) can be replaced by intravenous infusions. This can be either prophylactically or in response to bleeding. A complication of this treatment is formation of antibodies against the clotting factor resulting in the treatment becoming ineffective.
Acute episodes of bleeding or prevention of excessive bleeding during surgical procedures involve:
- Infusions of the affected factor (VIII or IX)
- Desmopressin to stimulate the release of von Willebrand Factor
- Antifibrinolytics such as tranexamic acid
Last updated April 2019