Question

A 14-year-old boy experiences severe prolonged bleeding following a tooth extraction. He also has a history of multiple episodes of painful joint swelling following minor trauma. His parents have no bleeding problems. Evaluation reveals that the patient has an inherited disorder and that one of his parents is a genetic carrier. Now his older sister, who does not have this condition, it pregnant (sex of the child unknown) and asks about the risk that her child will be affected. The best probable estimate that her child will have the disease is:

A. Near 0
B. 1/2
C. 1/4
D. 1.8
E. 1/16
F. 1/32

Answer 1

The 14-year-old boy likely has hemophilia, an X-linked recessive disorder. His sister's child, if male, has a 50% chance of being affected. The best estimate for the risk that her child will have the disease is 1/4, based on the provided options.

Step-by-step explanation:

The 14-year-old boy mentioned in the question likely suffers from hemophilia, a genetic disorder that affects blood clotting. Hemophilia is an X-linked recessive condition, usually passed from carrier mothers to their sons. As the boy's sister is not affected, she must be a carrier (since her brother is affected, and the disorder is rare in females who would require two defective X chromosomes to have the disease). The risk for her child to have hemophilia depends on the child's sex. If the child is male, there is a 50% chance he will inherit the affected X chromosome from his mother. If the child is female, there is no chance of being affected, but a 50% chance of being a carrier. Since the sex of the child is unknown, the best estimate combines the risk for both potential sexes. The risk is therefore 25% (1/4) that the child will be affected if the child is male, and 0% if the child is female, averaging to an overall 12.5% risk. However, to answer the question with the options provided, the closest estimate given would theoretically be 1/4 or 25%, assuming we are considering the risk for any child she has, ignoring the fact that for daughters the risk is 0%.