Haemophilia A and B
1. Big picture
Haemophilia A and B are inherited coagulation factor deficiencies causing secondary haemostasis failure.
The exam pattern is:
Boy + X-linked family history ± de novo mutation + deep tissue bleeding + haemarthrosis + prolonged activated partial thromboplastin time (aPTT) + normal prothrombin time (PT), thrombin time (TT), platelet count, and bleeding time → haemophilia.
| Disease | Missing factor | Other name | Frequency |
|---|---|---|---|
| Haemophilia A | Factor VIII (FVIII) | Classic haemophilia | More common |
| Haemophilia B | Factor IX (FIX) | Christmas disease | Less common |
Haemophilia A is about six times more common than haemophilia B; the textbook gives approximate incidences of 1/5000 male newborns for haemophilia A and 1/30000 for haemophilia B.
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