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WIREs Dev Biol
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Rare syndromes of the head and face—Pierre Robin sequence

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Abstract Pierre Robin sequence (PRS) is an association of clinical features consisting of mandibular hypoplasia, cleft secondary palate, and glossoptosis leading to obstructive apnea and feeding difficulties. PRS can occur as an isolated condition or can be found in association with a range of other features in a number of conditions including Treacher collins and Stickler syndromes. The frequent association of the PRS triad suggests a common underlying developmental mechanism which impacts on each of these tissues. Isolated PRS is typically sporadic but when familial usually exhibits autosomal dominant inheritance. The term PRS is applied on the basis of the pattern of malformation rather than etiology and growing evidence indicates that the initiating genetic lesion is variable. Various chromosomal anomalies have been associated with PRS including loci on chromosomes 2, 4, and 17. Associations with genes including SOX9, a number of collagen genes and work with animal models suggest the phenotype derives from a cartilage defect during early facial growth. However, alternative theories have been proposed and these highlight the difficulty of characterising congenital anomalies of craniofacial development in which multiple etiologies can result in very similar phenotypes. WIREs Dev Biol 2013, 2:369–377. doi: 10.1002/wdev.69 For further resources related to this article, please visit the WIREs website.

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(a) Illustration of the relationship between Meckel's cartilage and mandibular outgrowth in a Carnegie stage [CS 23, embryonic day (E) 56] human fetus. Meckel's cartilage initially forms as a rod within each mandibular arch. The left‐ and right‐side Meckel's cartilage fuse at the distal tip to form a ‘V’‐shaped structure that reflects the geometry of the prospective lower jaw. Mandibular outgrowth is strongly influenced by elongation of Meckel's cartilage in the sagittal plane (double arrow). (b) Morphological changes in oral structures immediately preceding palatal fusion viewed in the coronal plane. The palatal shelves emerge as an outgrowth of the maxillary arch at CS 21 (E51). Initial elongation of the palatal shelves at CS 22 (E53) is lateral to the tongue and in a vertical direction (arrow). Elongation of the mandible and flattening of the tongue at CS 23 (E56) increases oral volume sufficiently to allow the palatal shelves to attain a horizontal configuration and subsequent growth of the palatal shelves enables initial contact and adhesion of opposing epithelial surfaces. (c) Relationships between major oral structures in a mid‐sagittal plane of a normal (left) and Pierre Robin sequence (PRS) individual (right). The tongue attaches to the oral side of the mandible and under normal circumstances the oral volume is sufficient to sustain an open airway (red arrow). In PRS, reduced mandibular outgrowth compromises the normal increase in oral volume resulting in a relative macroglossia (large tongue). The tongue prevents elevation of the palatal shelves during embryonic development resulting in cleft palate and blocks the airway in the neonatal period. Hatched area represents the mandible. E, epiglottis; HP, hard palate; Hy, hyoid bone; M, Meckel's cartilage; Md, mandible; NC, nasal capsule; NS, nasal septum; OC, oral cavity; PS, palatal shelves; SP, soft palate; T, tongue; U, uvula.

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Birth Defects > Craniofacial and Nervous System Anomalies