A neonate has severe microcephaly, holoprosencephaly on ultrasound, bilateral microphthalmia, cleft lip and palate, and postaxial polydactyly. Which karyotype is expected?

• A 47,XX,+18
• B 47,XY,+13 ✓
• C 46,XY,del(5p)
• D 45,X

Explanation

This is the classic tetrad of trisomy 13 (Patau syndrome): central nervous system malformation with holoprosencephaly, ocular defects ranging from microphthalmia to cyclopia, cleft lip and palate, and polydactyly. Rocker-bottom feet and clenched overlapping fingers point to trisomy 18 instead, making option A the key distractor, but trisomy 18 lacks holoprosencephaly and polydactyly as cardinal features. Median survival in trisomy 13 is less than one month.

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.