Pierre Robin sequence
Pierre Robin sequence (PRS) is a genetic condition characterized by a smaller lower jaw (micrognathia). It is called a “sequence” because it comprises an initial anomaly that causes a series of other subsequent malformations.
In this case, micrognathia leads to downward displacement of the tongue, which in turn results in a malformation of the palate that creates a cleft palate.
Congenital defects do not always result from a single pathogenic source that causes a chain of subsequent disorders. For example, a syndrome is a condition in which all abnormalities originate from the same pathogenesis and occur simultaneously. An example of this is Down syndrome, in which all defects are caused by the same chromosome abnormality.
What are the symptoms?
In addition to micrognathia, symptoms include glossoptosis (a tongue that is downwardly displaced so that it falls back into the throat), an obstruction of the upper airway, and a cleft palate.
In severe cases with acute anatomical damage, swallowing difficulties and respiratory distress may also occur. In these cases, babies are fed using a special bottle. However, there is no need to give up breastfeeding since milk can be pumped and fed by a bottle.
Repeated ear infections are common in babies with Pierre Robin sequence. When untreated, these infections may lead to hearing impairments. Moreover, some babies require tracheostomy to bypass the airway obstruction and assist in breathing.
However, in most cases, micrognathia corrects itself as the child grows. Therefore, unlike other genetic diseases that require surgery for enlarging the jaw, in this case there is usually no need for such a procedure.
How is this condition inherited?
Most cases of Pierre Robin sequence are sporadic, which means they do not appear in other family members beside the patient. However, several hereditary cases of this condition were described.
An autosomal recessive inheritance pattern was described in some families, and x-linked inheritance in other families. Some of the inherited cases showed additional symptoms beside facial malformations, such as heart defects, club foot, and malformation of the fingers.
Therefore, parents who have one child with this condition are at a very low risk for it to appear in subsequent pregnancies. However, families with a child suffering from PRS and several other documented cases known in the family, have a 50% chance of having another child with this condition.
What is the genetic basis for Pierre Robin sequence?
The exact gene mutations that cause Pierre Robin sequence are still unknown, although the condition is probably caused by genetic mutations on chromosomes 2, 11, or 17.
However, in any case of a very small jaw finding, it is necessary to perform chromosome testing to rule out other disorders. In addition, further fetal testing is required to detect other relevant defects that may develop. These tests may include fetal echocardiography (to detect heart defects), and an ultrasound scan. Generally, Pierre Robin sequence occurs in one in 8,500 – 14,000 births.
