A couple has a child with Down syndrome confirmed as 46,XX,der(14;21)(q10;q10),+21 on karyotype. The father is phenotypically normal and carries a balanced Robertsonian translocation 14;21. What is the approximate recurrence risk of Down syndrome in future pregnancies?
- A Nearly zero because the father is unaffected
- B Approximately 10 to 15 percent
- C Approximately 1 to 5 percent ✓
- D 25 percent by Mendelian segregation
Correct answer: C. Approximately 1 to 5 percent
Explanation
When a parent carries a balanced Robertsonian translocation involving chromosome 21, the empirical recurrence risk for affected offspring is about 10 to 15 percent if the mother is the carrier but only about 1 to less than 5 percent if the father is the carrier, reflecting reduced transmission through sperm. This is why identifying which parent carries the translocation changes counselling. Mendelian segregation predicts far more gametes are unbalanced than result in liveborn affected children.
Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.