A mother notices a white pupillary reflex in the right eye of her 20-month-old child on photographs taken with flash. Examination shows strabismus and a white retinal mass behind the lens. Which cytogenetic locus is implicated?

• A Translocation t(11;22)(q24;q12)
• B Amplification of N-myc at chromosome 2p24
• C Deletion of RB1 gene at chromosome 13q14 ✓
• D Mutation of APC gene at chromosome 5q21

Explanation

Leukocoria in a toddler is retinoblastoma until proven otherwise. It arises from biallelic loss of the RB1 tumor suppressor gene located at 13q14, following either germline mutation plus somatic hit (heritable form) or two somatic hits (nonheritable form), per Knudson's two-hit hypothesis. N-myc amplification belongs to neuroblastoma, t(11;22) defines Ewing sarcoma, and APC mutation causes familial adenomatous polyposis, none of which produce leukocoria.

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.