An excess of amniotic fluid is a good diagnostic indicator. Several angle measures may help discern retrognathia, leading to screening of the cleft palate and the tongue position (posterior and high-up in the oral cavity). Prenatal diagnosis is possible if the retrognathia is detected on the strict profile of the fetus at ultrasound. 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. PRS often occurs as part of a complex malformation syndrome. It is more and more often evoked during prenatal life. Pierre-Robin sequence is usually diagnosed at birth based on clinical presentation. Only mutations in regulatory elements upstream from SOX9 were identified in families with PRS. Molecular identification of isolated PRS is rare. The mandibular growth defect can be either the consequence of antenatal orofacial hypomobility (usually related to a brainstem dysfunction, or from peripheral origin), or the consequence of a primary growth defect from tissue origin (bone, connective tissue). Mandibular hypoplasia, occurring early in gestation, causes the tongue to be maintained high-up in the oral cavity, preventing normal fusion of the palatal shelves (secondary palate). This condition is referred to as a sequence because the posterior cleft palate is a secondary defect associated with abnormal mandibular development and glossoptosis. At birth and during the first weeks of life, the main troubles are functional and include upper airway obstruction, difficulties in respiration, poor sucking and swallowing, reflux, oesophageal motor anomalies, and vagal syncope. Isolated Pierre Robin sequence (PRS), occurring without any other associated malformation, constitutes about 50% of cases presenting with these orofacial malformations.
However, precise values are difficult to obtain because historically the definition varied and studies often included cases which occurred as part of a recognised syndrome. The prevalence of this syndrome has been estimated at 1 in 10 000 births.
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