A 23-year-old woman comes to the physician at 9 weeks gestation for prenatal counseling. This is her first pregnancy. She has no history of bleeding, and there is no history of hemophilia in her husband's family. However, the patient's father and other relatives have hemophilia A, and she is concerned about the possibility of her child having the disease. The following pedigree is created according to the patient's family history (arrow points to the patient). Which of the following is the best response to this patient's concern?

Question

A 23-year-old woman comes to the physician at 9 weeks gestation for prenatal counseling.  This is her first pregnancy.  She has no history of bleeding, and there is no history of hemophilia in her husband's family.  However, the patient's father and other relatives have hemophilia A, and she is concerned about the possibility of her child having the disease.  The following pedigree is created according to the patient's family history (arrow points to the patient).  Which of the following is the best response to this patient's concern?

Quizplus · Accepted Answer

11ec25c8_d995_e9bc_bc81_ef052e899e5c_MD0003_00 Hemophilia A is an X-linked recessive disease caused by a deficit in coagulation factor VIII. All daughters born to a father with hemophilia A and an unaffected mother will be carriers. If the father has hemophilia A and the mother is a carrier, then half of the daughters will likely be carriers and the other half will likely inherit the mutation from both parents and have hemophilia themselves. This patient is a silent carrier of hemophilia A. Half of her sons will have hemophilia A, and the probability of having a male child is 50%; therefore, the overall probability of having a son with hemophilia is 25% and an unaffected son is 25% (0.5 x 0.5 = 0.25). As this patient is a carrier, half of her daughters will be asymptomatic carriers. The chance of having a girl is also 50%, which makes the chance of having a silent carrier daughter 25% and an unaffected daughter also 25%. (Choice A) Hemophilia is an X-linked recessive disorder and is much more common in males. (Choices B and D) On average, 25% of this patient's children would be expected to have hemophilia A, 25% would be silent carriers, and 50% would be unaffected. (Choice E) The incidence of hemophilia in the general population is <1%, but the probability of this patient having a child with hemophilia is 25%. Educational objective: Hemophilia A is an X-linked recessive disorder. On average, carrier mothers and unaffected fathers have a 25% chance of having a son with hemophilia, a silent carrier daughter, an unaffected son, or an unaffected daughter. References: Genetic counseling of hemophilia carriers (http://www.ncbi.nlm.nih.gov/pubmed/12640562) Hemophilia: in review (http://www.ncbi.nlm.nih.gov/pubmed/23818083)

A 23-Year-Old Woman Comes to the Physician at 9 Weeks