Prader Willi Syndrome

National Organization for Rare Disorders, Inc.

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It is possible that the main title of the report Prader Willi Syndrome is not the name you expected. Please check the synonyms listing to find the alternate name(s) and disorder subdivision(s) covered by this report.


  • Prader-Labhart-Willi syndrome
  • PWS
  • Willi-Prader syndrome

Disorder Subdivisions

  • None

General Discussion


Prader-Willi syndrome (PWS) is a genetic multisystem disorder characterized during infancy by lethargy, diminished muscle tone (hypotonia), feeding difficulties, and poor weight gain. In childhood, features of this disorder include short stature, small genitals and an excessive appetite because affected individuals do not feel satisfied after completing a mean (satiety). Without intervention, this can lead to overeating and the gradual onset of obesity. The food compulsion requires constant supervision. Individuals with severe obesity may have an increased risk of cardiac insufficiency, sleep apnea, diabetes, and other serious conditions that can cause life-threatening complications. All individuals with PWS have some cognitive impairment that ranges from low normal intelligence with learning disabilities to mild to moderate intellectual disability. Behavioral problems are common and can include temper tantrums, obsessive/compulsive behavior, and skin picking. Motor milestones and language development are often delayed. PWS occurs due to abnormalities affecting certain genes in a specific region of chromosome 15. These abnormalities usually result from random (sporadic) errors in development, but are sometimes inherited.


Originally described in the medical literature in 1956, PWS is the first disorder confirmed to be due to imprinting errors (see Causes section). It is the most common genetic cause of life-threatening childhood obesity. The disorder was once known as hypogonadism, hypotonia, hypomentia, obesity (HHHO).

Supporting Organizations

Foundation for Prader-Willi Research

5455 Wilshire Blvd
Suite 2020
Los Angeles, CA 90036
Tel: (760)536-3027
Fax: (888)559-4105

Genetic and Rare Diseases (GARD) Information Center

PO Box 8126
Gaithersburg, MD 20898-8126
Tel: (301)251-4925
Fax: (301)251-4911
Tel: (888)205-2311

International Prader Willi Syndrome Organization

c/o Baschirotto Institute for Rare Diseases (BIRD)
Via Bartolomeo Bizio, 1
Costozza (VI), 36023
Tel: 390444555557
Fax: 390444555557

March of Dimes Birth Defects Foundation

1275 Mamaroneck Avenue
White Plains, NY 10605
Tel: (914)997-4488
Fax: (914)997-4763

Medical Home Portal

Dept. of Pediatrics
University of Utah
Salt Lake City, UT 84158
Tel: (801)587-9978
Fax: (801)581-3899

NIH/National Institute of Child Health and Human Development

31 Center Dr
Building 31, Room 2A32
Bethesda, MD 20892
Fax: (866)760-5947
Tel: (800)370-2943

Prader-Willi France

10 Rue Charles Clement
Mondrepuis, F02500
Tel: 33323987904
Fax: 33323987904

Prader-Willi Syndrome Association (UK)

125A London Rd
Derby, DE1 2QQ
United Kingdom
Fax: 1332360401
Tel: 1332365676

Prader-Willi Syndrome Association (USA)

8588 Potter Park Drive, Suite 500
Sarasota, FL 34238
Tel: (941)312-0400
Fax: (941)312-0142
Tel: (800)926-4797

For a Complete Report

This is an abstract of a report from the National Organization for Rare Disorders (NORD). A copy of the complete report can be downloaded free from the NORD website for registered users. The complete report contains additional information including symptoms, causes, affected population, related disorders, standard and investigational therapies (if available), and references from medical literature. For a full-text version of this topic, go to and click on Rare Disease Database under "Rare Disease Information".

The information provided in this report is not intended for diagnostic purposes. It is provided for informational purposes only. NORD recommends that affected individuals seek the advice or counsel of their own personal physicians.

It is possible that the title of this topic is not the name you selected. Please check the Synonyms listing to find the alternate name(s) and Disorder Subdivision(s) covered by this report

This disease entry is based upon medical information available through the date at the end of the topic. Since NORD's resources are limited, it is not possible to keep every entry in the Rare Disease Database completely current and accurate. Please check with the agencies listed in the Resources section for the most current information about this disorder.

For additional information and assistance about rare disorders, please contact the National Organization for Rare Disorders at P.O. Box 1968, Danbury, CT 06813-1968; phone (203) 744-0100; web site or email

Last Updated:  12/10/1969
Copyright  2012 National Organization for Rare Disorders, Inc.