A child is brought to your clinic with spontaneous bleeding into the joint. Investigations shows prolonged aPTT and decreased level of factor VIII. What is the likely inheritance pattern of this disease?
**Core Concept**
Hemophilia A is a genetic disorder caused by a deficiency of factor VIII, a crucial clotting factor involved in the intrinsic pathway of blood coagulation. This deficiency leads to spontaneous bleeding into joints and muscles, as well as prolonged activated partial thromboplastin time (aPTT).
**Why the Correct Answer is Right**
The inheritance pattern of Hemophilia A is X-linked recessive, meaning the gene responsible for the condition is located on the X chromosome. Females can be carriers of the disease, while males are more frequently affected since they have only one X chromosome. The mutation in the F8 gene leads to the production of non-functional factor VIII, resulting in the prolonged aPTT and bleeding symptoms observed in affected individuals.
**Why Each Wrong Option is Incorrect**
**Option A:** Autosomal dominant inheritance would imply that both males and females have an equal chance of inheriting and expressing the condition, which is not the case in Hemophilia A.
**Option B:** Autosomal recessive inheritance would require two copies of the mutated gene (one from each parent) for the condition to be expressed, which is not the case in Hemophilia A.
**Option C:** X-linked dominant inheritance would imply that females are more frequently affected than males, which is not true in Hemophilia A.
**Clinical Pearl / High-Yield Fact**
Hemophilia A is often referred to as "Christmas disease" due to its association with bleeding into joints, particularly around Christmas time when children are more active. This condition is a classic example of an X-linked recessive disorder.
**Correct Answer:** C. X-linked recessive.