## **Core Concept**
The question tests understanding of X-linked recessive inheritance patterns and their association with bleeding disorders. X-linked recessive diseases are caused by mutations in genes on the X chromosome and predominantly affect males, who have only one X chromosome.

## **Why the Correct Answer is Right**
Hemophilia A, also known as classic hemophilia, is caused by a deficiency in **factor VIII**, a crucial protein for blood clotting. This condition is inherited in an X-linked recessive pattern, meaning the gene responsible for the condition is located on the X chromosome. Males are more frequently affected than females because they have only one X chromosome. If that chromosome has the mutation, they will express the condition since they do not have another X chromosome to compensate.

## **Why Each Wrong Option is Incorrect**
- **Option A:** While Hemophilia B (Christmas disease) is also an X-linked recessive disorder affecting males, it is caused by a deficiency in **factor IX**, not factor VIII. Thus, it does not match the description of the disease in the question.
- **Option B:** Von Willebrand disease is primarily inherited in an autosomal dominant pattern, not X-linked recessive. It results from a deficiency or dysfunction of **von Willebrand factor**, which plays a role in blood clotting. This does not fit the X-linked recessive pattern described.
- **Option D:** Factor XII deficiency is a condition that affects the intrinsic pathway of blood coagulation but is usually inherited in an autosomal recessive pattern and not specifically linked to X-linked recessive inheritance.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that patients with Hemophilia A may present with **spontaneous bleeding into joints or muscles** and have a prolonged **activated partial thromboplastin time (aPTT)** due to the deficiency of factor VIII. This condition is managed with replacement therapy using factor VIII concentrates.

## **Correct Answer:** .