**Question:** The most common coagulation disorders haemophilia A and Von Willebrand's disease are due to -

A. Deficiency in Factor VIII
B. Deficiency in Factor IX
C. Deficiency in von Willebrand factor
D. Other factors (not mentioned)

**Correct Answer:** A. Deficiency in Factor VIII

**Core Concept:**
Haemophilia A and Von Willebrand's disease are types of bleeding disorders caused by deficiencies in specific blood clotting factors. Haemophilia A is caused by deficiency in Factor VIII, while Von Willebrand's disease is caused by deficiency in von Willebrand factor. These factors play crucial roles in the clotting process, and their deficiencies lead to prolonged bleeding times and increased susceptibility to bleeding.

**Why the Correct Answer is Right:**
Haemophilia A is a genetic disorder that affects the blood clotting process. It is caused by a deficiency in Factor VIII, a coagulation factor involved in the intrinsic pathway of blood clotting. Factor VIII promotes the activation of Factor IX and stabilizes the activated form of Factor X, allowing the formation of a stable blood clot.

Von Willebrand's disease, on the other hand, is a genetic disorder that affects the blood clotting process as well. It is caused by a deficiency in von Willebrand factor, which is essential for platelet adhesion at the site of injury and helps in the maintenance of Factor VIII in the bloodstream. Von Willebrand factor plays a crucial role in the von Willebrand factor-platelet interaction, and its deficiency results in abnormal platelet adhesion, impaired clot formation, and prolonged bleeding times.

**Why Each Wrong Option is Incorrect:**

B. Deficiency in Factor IX: While Factor IX is involved in the clotting cascade, it is not the primary factor responsible for haemophilia A. Haemophilia A results from a deficiency in Factor VIII, not Factor IX.

C. Deficiency in von Willebrand factor: Von Willebrand's disease results from a deficiency in von Willebrand factor, not Factor VIII.

D. Other factors: The correct answers are already provided: deficiency in Factor VIII for haemophilia A and deficiency in von Willebrand factor for von Willebrand's disease. The other options (Factor IX or other unmentioned factors) are not the primary causes of these conditions.

**Clinical Pearls:**

1. Haemophilia A is an X-linked disorder caused by mutations in the F8 gene, encoding Factor VIII, resulting in impaired blood clotting and increased susceptibility to bleeding.
2. Von Willebrand's disease is an autosomal dominant disorder caused by mutations in the Von Willebrand factor (VWF) gene, leading to impaired platelet adhesion and clot formation, which results in prolonged bleeding times.

3. These disorders primarily affect males, as they are X-linked disorders. Haemophilia A and von Willebrand's disease are caused by mutations in X-linked genes, which means they