The neural crest and craniofacial malformations

The neural crest is a temporary embryonic structure that is composed of a population of multipotent cells that delaminate from the ectoderm by epitheliomesenchymal transformation (Sect. 5.2). Neural crest derivatives contribute to a large number of structures, including the spinal, cranial and autonomic ganglia, the enteric nervous system, the medulla of the adrenal gland, the melanocytes, dermal cells, corneal cells and many of the skeletal and connective tissues of the head (Sect. 5.3). The whole facial and visceral skeleton and part of the neurocranium are formed from the neural crest (Sect. 5.4).

A number of craniofacial malformations have major neural crest involvement, and are usually referred to as neurocristopathies (Sect. 5.5). Under this heading, the retinoic acid syndrome, the oculoauriculo-vertebral spectrum, Treacher Collins syndrome, the DiGeorge sequence and Waardenburg syndrome are discussed. A group of craniofacial disorders are the result of defects in primary cilia. These ciliopathies include Bardet-Biedl, Meckel-Gruber and Joubert syndromes (Sect. 5.6). Holoprosencephaly is an early disorder of pattern formation that may lead to closely related forebrain and facial malformations (Sect. 5.7). Abnormal development of the skull leading to craniosynostoses, craniofacial malformations due to agenesis or premature ossification of the cranial sutures, are discussed in Sect. 5.8. Several Clinical cases illustrate these disorders.