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Prader-Willi Syndrome
Wednesday, 02 July 2003
Wednesday, 06 July 2005


Prader-Willi Syndrome (PWS) is an inherited genetic disorder that is characterized by very low tone (hypotonia) and feeding problems in infancy followed by an uncontrollable appetite leading to obesity later in childhood. Children also are short, developmentally delayed, and have small hands, feet, and genitalia.


PWS occurs in all ethnicities and equally affects both males and females. The incidence is about 1 in 10,000 to 1 in 22,000 births.

Signs and Symptoms

PWS is present from birth. During pregnancy, the mother may have noticed that the baby did not move as much as in her other pregnancies. When they are born, they have very low tone (hypotonia) and cannot feed well. They have difficulty gaining weight initially but between 1 and 6 years of age, they start having an uncontrollable appetite and become obese. They have certain facial features such as a narrow forehead, almond-shaped eyes, and down-turned corners of the mouth. They may be short and have small hands, feet, and genitalia. Affected children have developmental delay especially in the area of speech, learning disabilities, or mental retardation. They may be stubborn, lie, steal, and have temper tantrums, or other behavior problems such as picking at their skin.

Possible Causes

There are different ways that PWS can be inherited. All of them involve an abnormality of chromosome 15. We each inherit two chromosome 15, one from our mother and one from our father. The most common cause of PWS which accounts for about 70% of cases results when a piece of chromosome 15 inherited from the father is missing (deleted). The second most common cause of PWS which accounts for about 25% of cases results when the child inherits both copies of chromosome 15 from the mother and none from the father. This is called uniparental disomy (UPD). The third most common cause of PWS which accounts for less than 5% of cases results when there is a chromosome 15 from each parent, but the one inherited from the father is not working properly. This is called an imprinting abnormality. There are other ways of inheriting PWS that are rare accounting for less than 1% of cases. Some cases of PWS have an unknown cause.


The diagnosis of PWS is based on having the above signs and symptoms. Genetic testing involving a blood test can confirm the diagnosis.


There is no cure for PWS. However, the child’s symptoms can be successfully managed with proper medical care and preventive measures. In infancy, feeding problems can be helped with special nipples or tube feeding. In childhood, growth hormone injections may be given to increase height and lean body mass. If the child has developmental delay, appropriate educational support and speech therapy is important. The major medical concern is obesity, which can lead to type 2 diabetes, high blood pressure, and heart disease. Affected individuals must consistently eat a balanced, low-calorie diet. They should have at least 30 minutes of exercise per day. They are always hungry and will do anything for food. These behaviors should be managed with behavior therapy techniques such as “time out”, limit-setting, and/or medication if needed. In adults, working or living in a sheltered environment, behavior management, and weight control programs are often successful in improving quality of life. Other treatments should be adjusted to the particular symptoms and needs of the individual.


With adequate weight control and management of symptoms, individuals with PWS can live a healthy life with a normal life expectancy. However, complications from obesity, type 2 diabetes, and heart disease can lead to early death.

Connect with other parents

In the spirit of community and support, Madisons Foundation offers the unique service of connecting parents of children with rare diseases. If you would like to be connected to other parents of children with this disease, please fill out this brief form.


Prader-Willi Association (USA)
Contains helpful resources, information, and support services.

National Library of Medicine: Prader-Willi Syndrome
A good website with information about PWS.

Prader-Willi Syndrome Association (UK)
A nice website with information about the syndrome as well as links to other useful sites.

Google Search for Prader-Willi Syndrome

References and Sources

OMIM: Prader-Willi Syndrome. McKusick, V. Gene Reviews: Prader-Willi Syndrome.