A newborn has upslanting palpebral fissures, a flat nasal bridge, a single transverse palmar crease, and hypotonia. Karyotype reveals 46 chromosomes with an extra copy of chromosome 21 material attached to chromosome 14 [rob(14;21)]. Which statement about this child's condition is correct?

• A This is standard trisomy 21 due to maternal meiotic nondisjunction
• B The extra chromosome 21 material arose from a mitotic error after fertilization
• C This represents a balanced translocation and the child is merely a carrier
• D The recurrence risk is higher if a parent carries a Robertsonian translocation ✓

Explanation

A Robertsonian translocation involving rob(14;21) results in Down syndrome due to three copies of chromosome 21 material. Unlike standard trisomy 21, this translocation form has a significantly elevated recurrence risk (up to 10-15% when the mother is a carrier, 2-3% when the father is a carrier). Standard trisomy 21 accounts for 95% of cases and has a low recurrence risk (~1%). The child is not balanced and is not phenotypically normal.

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.