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Pierre Robin sequence
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Pierre Robin sequence
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. Hearing loss and speech difficulty are often associated with PRS.[citation needed]
The physical craniofacial deformities of PRS may be the result of a mechanical problem in which intrauterine growth of certain facial structures is 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.[citation needed]
Alternatively, PRS may also be caused by a genetic disorder. In the case of PRS which is due to a genetic disorder, a hereditary basis has been postulated, but it usually occurs due to a de-novo mutation. Specifically, mutations at chromosome 2 (possibly at the GAD1 gene), chromosome 4, chromosome 11 (possibly at the PVRL1 gene), or chromosome 17 (possibly at the SOX9 gene or the KCNJ2 gene) have all been implicated in PRS. Some evidence suggests that genetic dysregulation of the SOX9 gene (which encodes the SOX-9 transcription factor) and/or the KCNJ2 gene (which encodes the Kir2.1 inward-rectifier potassium channel) impairs the development of certain facial structures, which can lead to PRS.
PRS may occur in isolation, but it is often part of an underlying disorder or syndrome. Disorders associated with PRS include Stickler syndrome, DiGeorge syndrome, fetal alcohol syndrome, Treacher Collins syndrome, and Patau syndrome.
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.[citation needed]
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. Fifty-three percent 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 two different hospitals in Boston, 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.[citation needed]
Gastroesophageal reflux (GERD) seems to be more prevalent in children with PRS. Because reflux of acidic contents in the posterior pharynx and upper airway can intensify the symptoms of PRS, specifically by worsening airway obstruction, it is important to maximize treatment for GER in children with PRS and reflux symptoms. Treatment may include upright positioning on a wedge (a tucker sling may be needed if the baby is in the prone position), small and frequent feedings (to minimize vomiting), and/or pharmacotherapy (such as proton pump inhibitors).[citation needed]
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Pierre Robin sequence
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. Hearing loss and speech difficulty are often associated with PRS.[citation needed]
The physical craniofacial deformities of PRS may be the result of a mechanical problem in which intrauterine growth of certain facial structures is 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.[citation needed]
Alternatively, PRS may also be caused by a genetic disorder. In the case of PRS which is due to a genetic disorder, a hereditary basis has been postulated, but it usually occurs due to a de-novo mutation. Specifically, mutations at chromosome 2 (possibly at the GAD1 gene), chromosome 4, chromosome 11 (possibly at the PVRL1 gene), or chromosome 17 (possibly at the SOX9 gene or the KCNJ2 gene) have all been implicated in PRS. Some evidence suggests that genetic dysregulation of the SOX9 gene (which encodes the SOX-9 transcription factor) and/or the KCNJ2 gene (which encodes the Kir2.1 inward-rectifier potassium channel) impairs the development of certain facial structures, which can lead to PRS.
PRS may occur in isolation, but it is often part of an underlying disorder or syndrome. Disorders associated with PRS include Stickler syndrome, DiGeorge syndrome, fetal alcohol syndrome, Treacher Collins syndrome, and Patau syndrome.
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.[citation needed]
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. Fifty-three percent 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 two different hospitals in Boston, 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.[citation needed]
Gastroesophageal reflux (GERD) seems to be more prevalent in children with PRS. Because reflux of acidic contents in the posterior pharynx and upper airway can intensify the symptoms of PRS, specifically by worsening airway obstruction, it is important to maximize treatment for GER in children with PRS and reflux symptoms. Treatment may include upright positioning on a wedge (a tucker sling may be needed if the baby is in the prone position), small and frequent feedings (to minimize vomiting), and/or pharmacotherapy (such as proton pump inhibitors).[citation needed]
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