What is PWS?

Prader-Willi syndrome (PWS) is a rare, complex genetic disorder that affects both males and females from birth and throughout their lives. It causes low muscle tone with consequent motor developmental delays, a mild to moderate learning difficulty, incomplete sexual development, and emotional and social immaturity, which can lead to challenging behaviours. During childhood, an overwhelming and insatiable chronic appetite usually develops which, without rigorous food management and exercise regimes, leads to food seeking, stealing and life threatening obesity. PWS occurs randomly in about 1:22,000 births and it is estimated that there are about 2,000 living with PWS in the UK.

 

 

Girl wearing orange PWSA tee-shirt smiling

Risk factors in Prader-Willi Syndrome

Serious illness or injury may be masked in people with Prader-Willi syndrome because of atypical biological responses:

Pain: A high pain threshold means people may not complain of pain even in serious injuries and illness. Complaints of pain should be taken seriously.

Temperature: In infections individuals may not develop a high temperature or may have a very low temperature. 

Failure to vomit: Many children and adults with PWS do not vomit which means that the presence / absence of vomiting is not a good guide to illness. However, some individuals with PWS do vomit.

Gastric Dilatation: There are a few case reports of severe gastric dilatation in people with PWS. In PWS, the stomach may empty more slowly than normal, so food and gas can build up. In rare cases, the stomach can become dangerously stretched.

This can cause people to go into shock and be life-threatening. This requires urgent medical attention.

Failure to vomit: Many children and adults with PWS do not vomit which means that the presence / absence of vomiting is not a good guide to illness. However, some individuals with PWS do vomit.

Gastric rupture:  A tear in the stomach is rare but there is an increased risk of this in PWS. It is life threatening and requires emergency medical treatment. Symptoms may or may not include vomiting, which is otherwise uncommon in PWS, and of blood, abdominal pain or no pain, sudden pallor and collapse or shock.

This may or may not be a consequence of a binge-eating episode.

Binge-eating episodes: If carers suspect that a binge-eating episode has occurred, they should be vigilant in their immediate supervision because of the risks of choking, gastric dilatation or gastric rupture, and seek emergency medical care if in doubt. They need to inform the emergency services about the association of these risks with PWS because professionals may be unfamiliar with PWS.

Choking : This is an increased risk in PWS (due to factors including rapid eating, thick saliva, not enough drink with food, weakness of pharyngeal muscles, and gastroesophageal reflux (GOR)). Families and carers need to be aware of emergency care for choking: What to do when someone is choking Choking first aid advice | British Red Cross.

Skin picking and sepsis:  Skin picking is a very common and difficult behaviour in PWS that is not fully understood. Carers and clinicians need to know or be informed that this can lead to local infection and to scarring and that occasionally it has resulted in sepsis with devastating outcomes. Skin picking risks must therefore be recognised and actively managed by clinicians in primary and secondary care.

Emergency information for healthcare staff

Take this document with you if you have to seek emergency care. It details the risk factors and features of PWS at a glance for medical staff to refer to. 

Find out more about Prader-Willi syndrome

  • Atypical PWS

    A few people have a PWS diagnosis, but do not have the typical physical features - in particular they may be taller than most people with PWS, even without growth hormone.

  • Incidence and Prevalence

    An epidemiological study carried out in one health region in the UK in 2000 estimated birth incidence to be in the region of 1:22,000, with a lower bound (ie the lowest number estimated) for population prevalence of 1:52,000. Previous estimates have estimated a birth incidence between 1:10,000 and 1:25,000. To give an idea of how rare PWS is, the incidence of Down Syndrome is 1:715 births – about 30 times more likely to happen than PWS. We estimate that there may be around 1500 – 2000 people with PWS in the UK of all ages; the PWSA UK is in touch with around 1,200 of these people and/or their families. Much of the uncertainty with regard to the statistics for incidence and prevalence is due to the fact that PWS may still go undiagnosed in some people, especially older adults; also, there is currently no central register held by the government of people diagnosed with rare syndromes.

  • Stages of Development

    Seven stages of development with regard to appetite and weight gain have been described by Dr Jennifer Miller and associates. 

    In an article in the Journal of Medical Genetics (2011), https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3285445/ 

    she describes these stages thus: 


    • Phase 0 occurs in utero, with decreased fetal movements and growth restriction compared to unaffected siblings. 
    • Phase 1 the infant is hypotonic and not obese, with sub-phase 1a characterized by difficulty feeding with or without failure to thrive (ages birth—15 months; median age at completion: 9 months). This phase is followed by sub-phase 1b when the infant grows steadily along a growth curve and weight is increasing at a normal rate (median age of onset: 9 months; age quartiles 5– 15 months). 
    • Phase 2 is associated with weight gain—in sub-phase 2a the weight increases without a significant change in appetite or caloric intake (median age of onset 2.08 years; age quartiles 20–31 months;), while in sub-phase 2b the weight gain is associated with a concomitant increased interest in food (median age of onset: 4.5 years; quartiles 3–5.25 years). 
    • Phase 3 is characterized by hyperphagia, typically accompanied by food-seeking and lack of satiety (median age of onset: 8 years; quartiles 5–13 years). Some adults progress to: 
    • Phase 4 which is when an individual who was previously in phase 3 no longer has an insatiable appetite and is able to feel full. It is important to note that it is very rare for someone with PWS to reach phase 4 and it is thought that most never will.