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What is PRS?

What is Pierre Robin Sequence?

This a very valid question. Most people have never heard of PRS and have never been given the opportunity to learn more about it.

It is referred to by various names including:

  • Pierre Robin Sequence
  • Pierre Robin Syndrome
  • Robin Anomalad
  • Robin Sequence
  • Pierre Robin Malformation Sequence and
  • PRS

Information for the condition is varied and conflicting.

The following information aims to provide valuable and meaningful information about PRS.

So what does PRS mean?

Pierre Robin (Pronounced Row-barn) Sequence (PRS) is a condition characterised by the existence of three abnormalities:

  1. a small or underdeveloped lower jaw (“micrognathia” pronounced micro-nath-ea)
  2. a tongue that is further back than usual ("glossoptosis")
  3. upper respiratory breathing obstruction.

 The existence of all three abnormalities together determines the diagnosis of Pierre Robin Sequence.  Although a cleft palate usually occurs in PRS, a cleft is not a necessary feature for diagnosis.  In the absence of a cleft a highly arched palate may occur.  

During the very early stages of pregnancy, a foetus jaw goes through a rapid growth period. In a child with PRS, this growth is restricted, resulting in the lower jaw being much smaller than it’s expected size.

The underdeveloped jaw causes the tongue to become crowded within the mouth. As a result the tongue sits high and is pushed backwards into the airway. The high position of the tongue then interferes with the closure of the palate.

The palate is generally formed at around 8-10 weeks gestation, when the two shelves of the palate grow and join at the midline forming the “roof of the mouth”.

In infants with PRS, the tongue has been pushed up high into this cavity preventing the joining of the plates, resulting a wide U shaped cleft of the soft and or hard palate.

After an infant is born a breathing obstruction also results from the position of the tongue within the mouth. Due to the small jaw, the tongue is also pushed further backwards into the airway, resulting in difficulty breathing. This is known as Upper Airway Breathing Obstruction.

Why is Pierre Robin called a “Sequence” not a “Syndrome”?

PRS is referred to as a “Sequence” not a “Syndrome” because the underdeveloped lower jaw begins a sequence of events, which leads to the abnormal placement of the tongue, resulting in the cleft palette and respiratory obstruction.

6 months.jpg

What causes PRS?

The exact cause for PRS is unknown.

There are many theories that exist as to why PRS occurs, however the exact cause has yet to be identified. However it is possible that a variety of factors may lead to the development of PRS.

Some of the most common theories include:

  • External factors such as over crowding in the uterus
  • Neurological conditions which lead to decreased movement of the jaw
  • A genetic abnormality exists in conjunction with PRS

More recent findings suggest that PRS is caused by the positioning of the head of the foetus in early pregnancy. Normally, during this phase of growth as the cervical vertebrae form, the infants head is pulled up off the chest. In infants with PRS, this development does not occur as expected and as a result, the jaw does not rise off the chest, instead it remains in an obstructed downward position. The small lower jaw causes the cascade of events, resulting in the three abnormalities of PRS.

Is PRS a genetic disorder?

Currently, there is no genetic test to determine the cause for PRS.  Researchers at the Murdoch Children's Research Institute are currently (2015) investigating some specific genes/chromosomes which may be involved, however research is still in its infancy.

It should be noted however that approximately 65% of children diagnosed with PRS are reported to have coexisting syndromes including Sticklers and Velocardial-facial Syndrome. These conditions do have a genetic origin with blood tests able to assist in the diagnosis of these conditions. 

You will be referred to a team of genetic specialists to help determine your infants individual diagnosis.

How common is PRS?

There are many varying statistics on the incidence of PRS in Australia, with numbers ranging from 1 in 8,500 to 14,000 live births. 

Research suggests that this condition is most prevalent in Anglo-Saxon children and affects both males and females equally.

How is PRS diagnosed?

Although the presence of a small jaw and sometimes a cleft palate may be seen with medical imaging during pregnancy, the diagnoses for PRS can only be truly made by examining your infant after birth, as only then can the level of obstruction (if any) be assessed.

Your doctor will examine and observe your baby to determine that the three elements of PRS, being a small lower jaw, tongue setback and airway obstruction are prevalent.

Diagnosis can occur shortly following birth or in some cases it may take a few days or even weeks to notice the airway obstruction.