A 22-year-old man presents with multiple odontogenic keratocysts of the jaw, bifid ribs, palmar pitting, and an early medulloblastoma. The mutated gene in this syndrome encodes the receptor for which morphogen?

• A Bone morphogenetic protein 4
• B Sonic hedgehog ✓
• C Wnt7a
• D Retinoic acid

Explanation

This is Gorlin (basal cell naevus) syndrome, caused by loss-of-function mutations in PTCH1, the transmembrane receptor for sonic hedgehog. In the resting state PTCH1 inhibits smoothened (SMO); when bound by SHH this inhibition is released and GLI target genes are activated. Loss of PTCH1 therefore mimics constitutive SHH signalling. The best distractor is APC, which causes familial adenomatous polyposis and acts in Wnt signalling, not in the hedgehog pathway.

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.