Class I: Palatal shelf hypoplasia

 

  • Fgfr2-/-
Class II: Palatal shelf fusion with the tongue or the mandible

 

  • Fgfr2R84C/R84C
  • Irf6-/-
Class III: Palatal shelves fail to meet at midline

 

Class IV: Submucosal cleft palate and/or persistence of medial edge epithelial cells

 

Illustrations from Chai & Maxson (2006).