Furthermore, the transcription factor Smad-interacting protein 1 (also known as SIP1 or ZEB2), a negative regulator of BMP4 signaling [39], is involved in the specification, differentiation, and migration of neural crest cells [40], and mutations in this gene are associated with Hirschsprung disease [41,42,43]. Here, ZEB2 is linked to Hirschsprung disease.