Robin syndrome

Pierre Robin sequence (/pjɛər rɔːˈbæ̃/; abbreviated PRS) is a congenital defect observed in humans which is characterized by facial abnormalities. The three main features are micrognathia (abnormally small mandible), which causes glossoptosis (downwardly displaced or retracted tongue), which in turn causes breathing problems due to obstruction of the upper airway. A wide, U-shaped cleft palate is commonly also present. PRS is not merely a syndrome, but rather it is a sequence — a series of specific developmental malformations which can be attributed to a single cause.PRS is characterized by an unusually small mandible, posterior displacement or retraction of the tongue, and upper airway obstruction. Cleft palate (incomplete closure of the roof of the mouth) is present in the majority of patients.The physical craniofacial deformities of PRS may be the result of a mechanical problem in which intrauterine growth of certain facial structures are restricted, or mandibular positioning is altered. One theory for the etiology of PRS is that, early in the first trimester of gestation, some mechanical factor causes the neck to be abnormally flexed such that the tip of the mandible becomes compressed against the sternoclavicular joint. This compression of the chin interferes with development of the body of the mandible, resulting in micrognathia. The concave space formed by the body of the hypoplastic mandible is too small to accommodate the tongue, which continues to grow unimpeded. With nowhere else to go, the base of the tongue is downwardly displaced, which causes the tip of the tongue to be interposed between the left and right palatal shelves. This in turn may result in failure of the left and right palatal shelves to fuse in the midline to form the hard palate. This condition manifests as a cleft palate. Later in gestation (at around 12 to 14 weeks), extension of the neck of the fetus releases the pressure on the mandible, allowing it to grow normally from this point forward. At birth however, the mandible is still much smaller (hypoplastic) than it would have been with normal development. After the child is born, the mandible continues to grow until the child reaches maturity.PRS is generally diagnosed clinically shortly after birth. The infant usually has respiratory difficulty, especially when supine. The palatal cleft is often U-shaped and wider than that observed in other people with cleft palate.The goals of treatment in infants with PRS focus upon breathing and feeding, and optimizing growth and nutrition despite the predisposition for breathing difficulties. If there is evidence of airway obstruction (snorty breathing, apnea, difficulty taking a breath, or drops in oxygen), then the infant should be placed in the sidelying or prone position, which helps bring the tongue base forward in many children. One study of 60 infants with PRS found that 63% of infants responded to prone positioning (Smith and Senders, 2006, Int J Pediatr Oto). 53% of the infants in this study required some form of feeding assistance, either nasogastric tube or gastrostomy tube feedings (feeding directly into the stomach). In a separate study of 115 children with the clinical diagnosis of PRS managed at 2 different hospitals in Boston (Evans et al., 2006, In J Pediatr Oto), respiratory distress was managed successfully in 56% without an operation (either by prone positioning, short term intubation, or placement of a nasopharyngeal airway). In this study, gastrostomy tube feeding were placed in 42% of these infants due to feeding difficulties.Children affected with PRS usually reach full development and size. However, it has been found internationally that children with PRS are often slightly below average size, raising concerns of incomplete development due to chronic hypoxia related to upper airway obstruction as well as lack of nutrition due to early feeding difficulties or the development of an oral aversion. However, the general prognosis is quite good once the initial breathing and feeding difficulties are overcome in infancy. Most PRS babies grow to lead a healthy and normal adult life.The prevalence of PRS is estimated to be 1 in 8,500 to 14,000 people.The condition is named for the French dental surgeon Pierre Robin.