A family shows autosomal dominant inheritance of fusion of fingers 3 and 4 with a single broad nail, and affected members have shortening of the metacarpals and metatarsals. Molecular testing reveals expansion of a polyalanine tract in which homeobox gene?
- A HOXB8
- B HOXA13
- C HOXD13 ✓
- D HOXA11
Correct answer: C. HOXD13
Explanation
Synpolydactyly is the classic human phenotype of expanded polyalanine tracts in HOXD13, a posterior HOXD gene expressed in the distal limb mesenchyme where it governs digit number and separation. HOXA13 polyalanine expansion instead causes hand-foot-genital syndrome with distal limb plus urogenital anomalies. HOXA11 and HOXB8 act more proximally in the forearm and specify forelimb versus hindlimb identity respectively, so they do not produce distal digital fusion.
Reference: Larsen's Human Embryology, 5th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.