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Isolated Pierre Robin syndrome
Pierre-Robin syndrome (or Pierre-Robin sequence) is characterised by triad of orofacial morphological anomalies consisting of retrognathism, glossoptosis and a posterior median velopalatal cleft. This condition is referred to as a sequence because the posterior cleft palate is a secondary defect associated with abnormal mandibular development: mandibular hypoplasia occurring early in gestation causes the tongue to be maintained high-up in the oral cavity, preventing fusion of the palatal shelves. The origin of the anomaly in mandibular development is variable but is rarely associated with an osseous defect. In most cases the mandibular malformation is a secondary defect resulting from antenatal orofacial hypomobility, usually related to a functional defect in the rhombencephalon (hind brain). This explains the frequency and severity of the manifestations in neonates, which include difficulties in coordinating suction, swallowing and respiration, early feeding difficulties, mis-swallowing, oesophageal motor anomalies, glossopharyngeal-laryngeal respiratory obstruction and vagal syncope. The prevalence of this syndrome has been estimated at 1 in 10 000 births, but precise values are difficult to obtain because the definition of the syndrome is variable, with some studies including cases were Pierre-Robin sequence occurs as part of a recognised syndrome. Isolated Pierre-Robin sequence (without any other associated malformation) occurs in about 50% of cases. Approximately 10% of these isolated forms are familial but the causative gene(s) has not yet been identified. If management of the clinical manifestations is successful during the first year of life, the prognosis is favourable. The glossoptosis, together with the feeding and respiratory problems, usually resolves during the first two years of life and growth of the mandible leads to correction of the retrognathism within three to six years. The cleft palate can be corrected by surgical intervention before the age of nine months. The neurological prognosis for these patients is also good. However, the persistent risk of otitis, transmission hypoacousia and phonation difficulties necessitate follow-up by an ear, nose and throat specialist and speech therapist. In one half of the cases, Pierre-Robin sequence occurs as part of a complex malformation syndrome. The nature of these anomalies is heterogeneous but they are most commonly collagenopathies, first arch anomalies, various chromosomal disorders (including Microdeletion 22q11), phenocopy syndromes associated with toxic agents (alcohol, sodium valproate) and other more complicated associations. The prognosis for patients with syndromic Pierre-Robin sequence varies depending on the syndrome involved. Pierre-Robin sequence is usually diagnosed at birth. Prenatal diagnosis is possible if the retrognathism is detected at ultrasound. An excess of amniotic fluid is a good diagnostic indicator. In contrast, the cleft palate is not directly visible but may be suspected if the position of the tongue is abnormal (posterior and high-up in the oral cavity). Genetic counselling should be offered to all families, even in the event of sporadic cases.