Summary of factors related to facial abnormalities discussed in the text
| Factor | Some Observed Abnormalities |
|---|---|
| RA | Excess leads to fusion of 1st and 2nd branchial arches and acoustic-facial ganglia, small jaws, cleft palate, deformed pinna (Treacher-Collins syndrome); RA controls Shh and Fgf8 levels |
| Fgf | Controls outgrowth of facial primordia and migration of neural (Fgf) crest cells to facial processes; a decrease in FBGFR1 leads to midline clefting and Kallmann syndrome, small face and skull, achondroplasia, Crouzon syndrome, Apert syndrome |
| TGF | TGFβ required for fusion of lateral palatal processes; a decrease leads to defects in maxillary and mandibular development |
| BMP | A decrease leads to short frontal and nasal bones and small pterygoid processes, short stature, ear defects, odontogenic patterning defects, slower neural tube closure, small branchial arches, loss of incisor teeth |
| Shh protein | A decrease leads to holoprosencephaly, hypotelorism; an increase leads to a wide forehead, frontonasal dysplasia, Gorlin syndrome, Grieg cephalopolysyndactyly, Smith-Lemli-Opitz syndrome |
| Wnts | A decrease leads to loss of teeth, truncation of jaw, mesencephalic nucleus, and trigeminal nerve |
| ET-1 | A decrease leads to aplasia of 1st and 2nd arches, defects in maxilla and cleft palate, malformations of middle and external ear; 22q11.2 deletion syndrome (CATCH22 syndrome) |
| Jagged 1 and 2 | A decrease leads to Alagille syndrome, failure of palatal shelves to elevate, and fusion of shelves with tongue |
| Platelet-derived growth factors | A decrease leads to loss of some facial bones |
| Homeobox-containing genes | A decrease leads to primitive facial morphology, cleft palate, short maxilla and mandible, loss of maxillary molar teeth, ankyloglossia |
Note:—RA indicates retinoic acid; FGFR, fibroblast growth factor receptor; PDGFR, platelet-derived growth factor receptor.