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Prader-Willi Syndrome

Fact Sheet

What is Prader- Willi Syndrome?

Prader-Willi Syndrome (PWS) is a genetic disorder that affects males and females with equal frequency and affects all races and ethnicities. The syndrome is recognized as the most common genetic cause of obesity.

The symptoms of PWS are caused by the dysfunction of a portion of the brain called the hypothalamus. The hypothalamus is a small endocrine organ at the base of the brain that plays a crucial role in many bodily functions, such as hunger and satiety, temperature regulation, vomiting, fluid balance, puberty, and fertility.

How is it manifested?


  • hypotonia (weak muscle tone)
  • difficulty with feeding because of poor sucking ability
  • delayed motor and language development
  • respiratory difficulties

Children and Adults

  • short stature, small hands and feet (without growth hormone treatment)
  • intellectual impairment
  • learning deficits such as poor short term memory, difficulty with auditory discrimination
  • increased risk of obesity because of a persistent sense of hunger and lack of satiation (hyperphagia), low metabolic rate (60%) and high fat-to-muscle ratio
  • serious health problems if weight is not controlled (e.g., diabetes, cardiac and respiratory complications)
  • behavioural problems

Who is affected?

The current incidence of Prader-Willi Syndrome is 1 in 15,000 live births.

How is it diagnosed or detected?

A suspected diagnosis of PWS is usually made by a physician based on clinical symptoms. The diagnosis is then confirmed by a blood test. Families who are seeking a diagnosis or who have concerns about the risks should work with a genetics specialist who is knowledgeable about PWS and the latest in testing. The geneticist will arrange to have blood samples sent to an appropriate laboratory for testing.

Additional Resources:

Ontario Prader-Willi Syndrome Association (OPWSA)
OPWSA is a non-profit charity. Their mission is to enhance the quality of life for individuals with Prader-Willi Syndrome. This website contains information for those interested in and affected by Prader-Willi Syndrome and has a support group for parents.

Canadian Prader-Willi Syndrome Organization (CPWSO)
CPWSO is a national, charitable association, dedicated to serving individuals affected by Prader-Willi Syndrome (PWS), their families and interested professionals. Some of the organization’s objectives include promoting broader geographic interest in PWS, seeking increased diagnosis in infancy, liaising with the International Prader-Willi Syndrome Organization and with national affiliates around the world who share similar goals.

International Prader-Willi Syndrome Organization (IPWSO)
IPWSO is an international organization, whose members are the national Prader-Willi Syndrome Associations. IPWSO is committed to enhancing the quality of life for people with PWS and their families, giving these children the best possible opportunities for living their lives to the fullest.

PWS Notes is designed to provide useful background on Prader–Willi Syndrome for parents and to organize medical information that may be helpful for future research directions. This resource was created by a PWS Mom and is particularly dedicated to the new generation of PWS children who are receiving the advantages of early interventions.

Books and Online literature:

Prader-Willi Syndrome-Guide 2005: A Guide for Families and Professionals
By Dr. M. A. Angulo (available at

Management of Prader-Willi Syndrome
By Merlin G. (EDT) Butler, Phillip D. K. Lee, and
Barbara Y. (EDT) Whitman

Prader-Willi Syndrome: Development and Manifestations
By Joyce Whittington and Tony Holland

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