Prader-Willi Syndrome


What is Prader-Willi syndrome?

Prader-Willi syndrome (PWS) is a rare genetic condition that affects a child’s metabolism and causes changes in the child’s appearance and behavior. It is marked by a low muscle tone and poor feeding during early infancy, followed by tremendous appetite after age 2-3 years, which leads to the child becoming overweight.

PWS may also cause a delay in childhood milestones and puberty. If abnormal weight gain is not controlled, it may lead to life-threatening complications such as sleep apnea, diabetes and heart problems.

Who is affected by Prader-Willi syndrome?

Anyone can develop PWS. The condition occurs in one out of every 12,000–15,000 births, and affects equal numbers of boys and girls.

Symptoms and Causes

What causes Prader-Willi syndrome?

PWS occurs when certain sequences of genetic material are missing or not working--specifically, a segment on chromosome 15. The mother and father each pass down one copy of chromosome 15 to their children. In children who have PWS, the father’s chromosome is not working properly. In some cases, children inherit two copies of chromosome 15 from their mother.

What are the symptoms of Prader-Willi syndrome?

PWS affects each individual differently. Symptoms usually appear in infancy, and may include:

  • A weak cry
  • Unusual facial features, such as almond-shaped eyes and a long, narrow head
  • Lethargy (tiredness, listlessness)
  • Poor feeding ability
  • Weak muscle tone (hypotonia)

As a child with PWS ages, other symptoms begin to appear, including:

  • Behavioral and emotional problems
  • Intellectual disability
  • Problems with eating, including: not feeling satisfied after eating, and eating an unusually large amount of food (hyperphagia). Hyperphagia may lead to morbid obesity, which increases the likelihood of other complications, such as diabetes.
  • Short height with small hands and feet
  • Underdeveloped genitals

Diagnosis and Tests

How is Prader-Willi syndrome diagnosed?

The doctor will conduct a physical examination and review the child’s medical history. The doctor will also order a blood test to look for changes or mistakes in the chromosomes.

Management and Treatment

How is Prader-Willi syndrome treated?

Treatment focuses on managing symptoms and preventing complications. The child’s treatment may involve the following:

  • Devices, such as special bottle nipples, to help infants get enough nutrition
  • Helping the child eat properly, including a low-calorie diet and controlling how much he or she eats
  • Medications to increase amounts of certain hormones, such as growth hormone, and testosterone or human chorionic gonadotropin for boys and estrogen for girls
  • Supportive therapies such as physical therapy, speech-language therapy, and special education.

What complications are associated with Prader-Willi syndrome?

Many individuals with PWS develop obesity from overeating. Obesity is associated with many complications, including:

Outlook / Prognosis

What is the prognosis (outlook) for people with Prader-Willi syndrome?

With early and ongoing treatment, many individuals with Prader-Willi syndrome live a normal lifespan. Each person with PWS needs lifelong support to achieve as much independence as possible.

Living With

What questions should I ask my doctor about Prader-Willi syndrome?

  • How can I help my child avoid obesity?
  • What will my child’s treatment involve?
  • What kinds of behavioral issues might my child have?
  • Are there support groups to help us learn about and cope with PWS?
  • Should others in my family have genetic testing?

Last reviewed by a Cleveland Clinic medical professional on 12/14/2018.


  • Foundation for Prader-Willi Research. About Prader-Willi Syndrome. ( Accessed 12/17/2018.
  • Prader-Willi Syndrome Association. PWS Basic Facts. ( Accessed 12/17/2018.
  • National Organization for Rare Disorders. Prader-Willi Syndrome. ( Accessed 12/17/2018.
  • U.S. National Library of Medicine. Genetics Home Reference. Prader-Willi syndrome. ( Accessed 12/17/2018.

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