A 34-year-old, G, P0, presents for genetic counselling at 12 week’s gestation. The patient has two sisters and a brother; her father has haemophilia. Her siblings are not affected, but she has a nephew that is:
**Core Concept**
Haemophilia A is an X-linked recessive genetic disorder caused by a deficiency of factor VIII, leading to prolonged bleeding. The disease affects males more frequently than females due to the presence of two X chromosomes in females, which usually compensates for the mutated gene.
**Why the Correct Answer is Right**
In this case, the patient has a family history of haemophilia, with her father being affected. Since haemophilia A is X-linked recessive, the patient has a 50% chance of being a carrier and passing the mutated gene to her offspring. The presence of an affected nephew suggests that the patient is a carrier. This is because the nephew's father (the patient's brother) is not affected, indicating that the patient's brother is not a carrier. However, the patient's sister, who is a carrier, could have passed the mutated gene to her son (the patient's nephew), making him affected.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is not provided, so we'll skip it.
**Option B:** This option is also not provided, so we'll skip it.
**Option C:** This option is not provided, so we'll skip it.
**Clinical Pearl / High-Yield Fact**
In X-linked recessive disorders like haemophilia, females can be carriers and may pass the mutated gene to their offspring, while males are more frequently affected due to the lack of a second X chromosome.
**Correct Answer:** Not provided, but based on the information, the correct answer would be related to the patient being a carrier of the mutated gene.