Cytogenetics: Down syndrome: practice question

A Pathology question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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Pathology · Cytogenetics: Down syndrome

Sample item

A neonate with typical features of Down syndrome is born to a 24-year-old woman. Karyotype shows a Robertsonian translocation between chromosomes 14 and 21 together with an extra copy of chromosome 21 material, 46,XY,der(14;21)(q10;q10),+21. What is the most appropriate next step?

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

A. Karyotype both parents, because a balanced carrier raises the recurrence risk well above the age-related risk

Down syndrome from a Robertsonian translocation involving chromosome 21 can be inherited from a balanced carrier parent, who is clinically normal with 45 chromosomes. The recurrence risk is much higher than the usual risk related to age, so parental karyotyping is essential for genetic counselling. Trisomy 21 from non-disjunction has a low recurrence risk.

Option by option

  • A. Karyotype both parents, because a balanced carrier raises the recurrence risk well above the age-related risk (correct)

    Correct. Parental karyotypes identify a balanced carrier and guide counselling and prenatal testing.

  • B. Perform maternal serum alpha-fetoprotein in the next pregnancy only

    Alpha-fetoprotein is a screening test and does not answer the question of carrier status.

  • C. Reassure the family that recurrence risk is the same as in the general population

    Recurrence risk is substantially higher when a parent carries the translocation.

  • D. No testing is needed because Robertsonian translocations are always de novo

    A proportion of these cases are inherited, so parents must be tested.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

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Questions about this Pathology question

What is the answer to this Pathology question?

The best answer is A, Karyotype both parents, because a balanced carrier raises the recurrence risk well above the age-related risk. Down syndrome from a Robertsonian translocation involving chromosome 21 can be inherited from a balanced carrier parent, who is clinically normal with 45 chromosomes.

Why is "Perform maternal serum alpha-fetoprotein in the next pregnancy only" not the answer?

Alpha-fetoprotein is a screening test and does not answer the question of carrier status.

Why is "Reassure the family that recurrence risk is the same as in the genera…" not the answer?

Recurrence risk is substantially higher when a parent carries the translocation.

Why is "No testing is needed because Robertsonian translocations are always d…" not the answer?

A proportion of these cases are inherited, so parents must be tested.

What concept does this question test?

It tests Cytogenetics: Down syndrome in Pathology. The recurrence risk is much higher than the usual risk related to age, so parental karyotyping is essential for genetic counselling. Trisomy 21 from non-disjunction has a low recurrence risk.

How hard is this question?

We tag it as a multi-step question: it asks you to combine more than one idea. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Cytogenetics: Down syndrome?

Learn each disease as a bundle: cause, key histology, markers, and the clinical hallmark. Then use the flashcards and the other Pathology questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.