**Question:** Gene responsible for Van der Woude syndrome:

A. PITX2
B. IRF6
C. TBX1
D. FGFR2

**Correct Answer:** B. IRF6

**Core Concept:** Van der Woude syndrome is a rare autosomal dominant disorder characterized by cleft lip/palate and jaw abnormalities. It is caused by mutations in the IRF6 gene, which encodes a transcription factor involved in craniofacial development and extracellular matrix organization.

**Why the Correct Answer is Right:** IRF6 (Interferon Regulatory Factor 6) is an essential gene for normal development of the face, lip, and palate. Mutations in IRF6 lead to an abnormal transcription factor, which disrupts the proper formation of these structures during embryonic development. This results in the characteristic features of Van der Woude syndrome.

**Why Each Wrong Option is Incorrect:**

A. PITX2 (Pituitary Transcription Factor 1) is involved in pituitary development and function, not craniofacial development. PITX2 mutations are associated with Axenfeld-Rieger syndrome, not Van der Woude syndrome.

C. TBX1 (T-box Transcription Factor 1) is involved in thymus, heart, and limb development. It is associated with DiGeorge syndrome, not Van der Woude syndrome.

D. FGFR2 (Fibroblast Growth Factor Receptor 2) is involved in bone and cartilage development, not craniofacial development. Mutations in FGFR2 cause Crouzon syndrome, not Van der Woude syndrome.

**Clinical Pearl:** IRF6 mutations should raise suspicion for Van der Woude syndrome in a patient presenting with cleft lip/palate and jaw abnormalities. Early diagnosis and counseling is crucial for affected individuals and their families.