Consanguineous Couple With a Child With Beta-Thalassemia Major
A 29-year-old woman comes for genetic counseling at 10 weeks of pregnancy. She and her husband are first cousins. They have a 3-year-old daughter with beta-thalassemia major who receives transfusions every three weeks and chelation. Their 1-year-old son is healthy but has microcytic anemia. The woman's hemoglobin is 10.2 g/dL, MCV 64 fL, and HbA2 5.1%; her husband's hemoglobin is 11.0 g/dL, MCV 66 fL, HbA2 4.8%. The daughter's DNA study shows homozygous beta-globin gene mutations. The couple wants to know whether the pregnancy can be tested and whether the result would change management. They are worried about stigma and about the cost of another affected child. The husband asks whether his low MCV could be due to iron deficiency instead.
1. Interpret the parents' MCV and HbA2 results and explain why both are likely beta-thalassemia carriers rather than iron deficiency.
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Both parents have microcytic anemia with HbA2 above 3.5%, which is typical of beta-thalassemia trait. Iron deficiency usually lowers HbA2 and does not explain HbA2 5.1% or 4.8%. The daughter's homozygous beta-globin mutations confirm that both parents are carriers. The son's microcytosis should be evaluated with ferritin and HbA2, but he is at 25% risk of being affected and 50% risk of being a carrier. Consanguinity does not cause thalassemia, but it increases the chance that both parents share the same recessive allele.
2. What is the recurrence risk for this pregnancy, and what prenatal test is feasible at this gestational age?
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Each pregnancy has a 25% risk of affected, 50% carrier, and 25% unaffected. At 10 weeks, chorionic villus sampling can be performed at 11-14 weeks, after the daughter's mutations are identified; amniocentesis is an alternative later. DNA analysis of the pregnancy can distinguish affected from carrier. Counseling should be nondirective, presenting prenatal diagnosis, continuation, and preparation for care as options. The result may change management but does not obligate termination.
3. How would you counsel the couple about the healthy son and about stigma and cost without directing their choice?
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Counsel that carrier status is not disease and does not require transfusions; the son should be tested with CBC, ferritin, and HbA2, and if microcytosis persists, DNA testing. Address stigma by explaining that thalassemia is inherited, not contagious, and that carriers can live normally. Discuss the financial and emotional burden of another affected child, but do not pressure. Offer genetic counseling for relatives and discuss prenatal diagnosis as a choice. Document that the couple understands the 25% risk and the limits of testing.