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.

 

 

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.

  • Acquired PWS

    PWS-like symptoms can be "acquired" by damage to the hypothalamus during a person's life, such as head injury or surgery, or from a dysfunction of the hypothalamus. In these cases, the person does not have any of the genetic abnormalities and few of the physical characteristics of PWS, but acquires some or all of the behavioural and appetite problems which are associated with the syndrome. Management techniques used with people with true PWS can also be helpful in acquired PWS.

  • 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.