Which of the following syndromes is characterized by mandibular hypoplasia (micrognathia) present at birth?

Pierre Robin sequence (PRS) is defined by the triad of micrognathia (severe mandibular hypoplasia), glossoptosis (posterior displacement of the tongue), and often a U-shaped cleft palate. The mandibular hypoplasia is the initiating anomaly, causing the tongue to be displaced posteriorly, which then prevents palatal shelf closure. Infants with PRS may have airway obstruction. Crouzon syndrome involves craniosynostosis with maxillary hypoplasia but normal mandible. Down syndrome (trisomy 21) involves macroglossia relative to the smaller jaw. Treacher Collins syndrome involves bilateral malar and mandibular hypoplasia but is classified separately from PRS.