Prader-Willi Syndrome


The Questions and Answers that follow aim to provide an introduction to Prader-Willi syndrome (PWS) for parents and other family members. Following those, we offer links to selected resources for more information and support and a list of valuable services.
More information about many topics relevant to children with PWS and many other chronic conditions and their families can be found in the left menu. Detailed information aimed at primary care doctors can be found in our Prader-Willi Syndrome module.

What is Prader-Willi syndrome (PWS) and what causes it?

PWS is a complex genetic disorder affecting appetite, growth, metabolism, cognitive function, and behavior.

What are the symptoms of Prader-Willi syndrome?

Individuals with PWS typically have low muscle tone, short stature, incomplete sexual development, cognitive disabilities, problem behaviors, and the hallmark characteristics - involuntary and uncontrollable feelings of hunger and a slowed metabolism that can lead to excessive eating and life-threatening obesity. Those who have PWS need intervention and strict external controls, which may include padlocking access to food, to maintain normal weight and to help save their lives.

How is it diagnosed?

Suspicion of the diagnosis is first assessed clinically (based on direct observation of the patient), then confirmed by specialized genetic testing on a blood sample.

What is the prognosis?

If obesity is controlled, life expectancy is normal or near normal.

What is the risk for other family members or future babies?

Most cases of PWS are sporadic; however, at least 20 families have been reported with more than one affected member, including reports in twins. The chance for familial recurrence is estimated to be less than 1%. However, this risk may be as high as 50% in some families where an imprinting defect causes defective control of differentially expressed genes in both the child with PWS and the unaffected father.

What treatments/therapies/medications are recommended or available?

Although there is no cure for Prader-Willi syndrome (PWS), there are interventions that can significantly help individuals with PWS lead healthier lives. An example is growth hormone (GH) therapy to increase stature, decrease obesity, and increase muscle mass and capacity for physical activity. The management of individuals with PWS is enhanced by a multi-disciplinary approach that includes nutrition, neurology, endocrine, genetics, ophthalmology, psychology, gastroenterology, speech, occupational and physical therapy, and orthopedics. The collaboration of these specialists in a PWS-focused clinic setting offers benefits for patients/families and for developing ongoing improvements in care.
General health is usually good in individuals with PWS. If weight is controlled, life expectancy may be near normal and the individual's health and functioning maximized. The constant need for food restriction and behavior management may be stressful for family members. The national Prader-Willi Syndrome Association (USA) can provide information and support for family members and healthcare providers. See Prader-Willi Syndrome Association (USA).

How will my child and our family be impacted?

The family will need to be aware of the behaviors and conditions associated with PWS. The family and other caregivers can support treatment and therapy plans; watch for injurious behaviors and symptoms of complications; and help provide an environment with consistent routines and expectations. The siblings may need support services.

When does PWS occur?

The prevalence of PWS is approximately 1/25,000. [Butler: 1990] Although considered a "rare" disorder, PWS is one of the common conditions seen in genetic clinics and is the most common genetic cause of obesity identified thus far.

Why does PWS occur?

Most cases of PWS are attributed to a spontaneous genetic error that occurs at or near the time of conception for unknown reasons. In a small percentage (< 2%) of individuals with PWS, a genetic mutation from the parent causes PWS in the child. It is important to identify these children as other children in the family may also be affected. A PWS-like disorder, 'acquired PWS' can also develop after birth if a part of the brain called the hypothalamus is damaged by injury or surgery.

How does the genetic error cause PWS?

The occurrence of PWS is due to the lack of several genes on one of an individual's two chromosome 15s - the one normally contributed by the father. In most cases, there is a deletion - the critical genes are somehow missing from the chromosome. The critical paternal genes lacking in individuals with PWS have a role in the regulation of appetite. This is an area of active research in a number of laboratories around the world, since understanding the defect may be helpful not only to those with PWS but to understanding obesity in otherwise normal individuals.
Individuals with PWS have a flaw in the part of their brain called the hypothalamus, which normally registers feelings of hunger and satiety. While the problem isn't fully understood, it is apparent that people with this flaw never feel full; they have a continuous urge to eat that they can't learn to control. To compound this problem, children with PWS need less food than typically developing children because their bodies have less muscle and tend to burn fewer calories. Parts of the hypothalamus are also related to rage and other behavior problems.

What does human growth hormone do for people with PWS?

Use of recombinant human growth hormone (rhGH) is becoming standard of care for children with PWS. It should be prescribed with appropriate precautions by an experienced endocrinologist. Human growth hormone increases growth rate, particularly in the first year of treatment, and improves body composition so that muscle mass is increased and fat mass is decreased. Children treated with rhGH have improved energy and physical activity levels; improved strength, agility, and endurance; and improved respiratory function. For unknown reasons, it may also help with cognitive development.

What is "Food Security"?

The psychological concept of food security is an essential component of the management of individuals with PWS; the goal is to maintain food security across all settings. Food security is one of the most basic skills taught to the family or other caretakers.
Food security is achieved when food access is controlled to the extent that three criteria are established:
  1. There is no doubt when, what, and how much the person with PWS will eat;
  2. There is no hope of receiving any more; and
  3. There is no disappointment due to false expectations.
Food security = No doubt + No hope + No disappointment.
When food access is restricted, individuals with PWS require no doubt about their meals and snacks. Menus are planned ahead and posted; calories are controlled, but the amount of food presented can still be generous. Although the timing of the meals and snacks remains fixed, it is not focused on the clock; it is set by the sequence of activities across the day. This concept is critical to the achievement of flow through the day.

Does the overeating with PWS begin at birth?

No, in fact newborns with PWS often have difficulty obtaining enough nourishment because low muscle tone impairs their sucking ability. They may be said to have "failure to thrive," which means not gaining expected growth. Many require special feeding techniques or tube feeding for several months or more after birth until muscle control improves. Sometime in the following years, usually before school age, children with PSW develop an intense interest in food and can quickly gain excess weight if calories aren't restricted.

Do diet medications work for the appetite problems in PSW?

Unfortunately, no appetite suppressant has worked consistently for people with PWS. Most require an extremely low-calorie diet all their lives and must have their environments designed so that they have very limited access to food.

What is the Red, Yellow, Green System of weight management?

The Red, Yellow, Green System (RYG) was originally developed for obesity management in preteens. The system has been adapted for individuals with PWS as a way to put necessary limits and structure in place. RYG is effective for the prevention and treatment of obesity and also decreases food-centered behaviors.

What kinds of behavior problems do people with PWS have?

In addition to involuntary focus on food and food-centered behaviors, individuals with PWS tend to have obsessive/compulsive behaviors not related to food, including repetitive thoughts and verbalizations; collecting and hoarding possessions; picking at skin irritations; and a strong need for routine and predictability. ADHD may also be present. Frustration or changes in plans can easily set off a loss of emotional control that ranges from tears to temper tantrums to physical aggression. The essential strategies for minimizing difficult behaviors in PWS are careful structuring of the person's environment and consistent use of positive behavior management and supports.

Does early diagnosis help?

While there is no medical prevention or cure, early diagnosis of PWS gives parents time to learn about and prepare for the challenges that lie ahead and to establish family routines that will support their child's diet and behavior needs from the start.

How do I help my other children deal with having a sister or brother with PWS?

Research on families with children with various disabilities often finds that children are strengthened, not harmed, by having a sibling with special needs, although having a sibling with disabilities makes life more complicated. Sibling workshops have been designed to help with those problems (for example see Sibshops: workshops for siblings of children with special needs) and, for some problems, individual or family counseling may be necessary. For an interesting viewpoint, try the book The Normal One, written by a typically developing sibling of a child with disabilities. [Safer: 2002]

What does the future hold for people with PWS?

With help, individuals with PWS can expect to accomplish many of the things their "normal" peers do - complete school, participate in their outside areas of interest, be a productive worker under the right conditions, even move away from the family home. They do, however, need a significant amount of support from their families and from school, work, and residential service providers, both to achieve these goals and to avoid obesity and the serious health consequences that accompany it. Even those with IQs in the normal range need lifelong diet supervision and protection from food availability. Although in the past many people with PWS died in adolescence or young adulthood, prevention of obesity can offer those with the syndrome the probability of having a normal life span.


Information & Support

Where can I go for further information?

For Parents and Patients


National Organization of Rare Disorders (NORD)
Provides advocacy, education, and other services for people affected by rare diseases.

Prader-Willi Syndrome Association (USA)
A strong national organization of families and professionals, PSWA offers a toll-free helpline, a bimonthly newsletter and numerous publications about PWS, an annual family conference and scientific meeting, and chapters throughout the country to provide local family support and advocacy.

Heartland Genetic Services Network
Region 5 of the Genetic Service Networks; provides information for families and providers including listings of local resources.


Prader-Willi Syndrome (Genetics Home Reference)
Excellent, detailed review of condition for patients and families; sponsored by the U.S. National Library of Medicine.

Prader-Willi Syndrome (MedlinePlus)
Information about PWS and links to other reliable sources of information; sponsored by the National Library of Medicine.

Supplemental Security Income Guide for Children with PWS (PWSA)
Information and downloadable documents for preparing a Supplemental Security Income (SSI) form; Prader-Willi Syndrome Association.

Prader-Willi Syndrome Educational Downloads (Pittsburgh Partnership)
Information for providers and families regarding food security, behavioral management, nutrition/weight management, and other issues in individuals with PWS; from the Pittsburgh Partnership, which provides education and consultation.

Services for Patients & Families Nationwide (NW)

For services not listed above, browse our Services categories or search our database.

* number of provider listings may vary by how states categorize services, whether providers are listed by organization or individual, how services are organized in the state, and other factors; Nationwide (NW) providers are generally limited to web-based services, provider locator services, and organizations that serve children from across the nation.


Angelman, Rett, and Prader-Willi Syndromes Research Consortium
An integrated group of academic medical centers, patient support organizations, and clinical research resources dedicated to conducting clinical research in genetic and neurodevelopmental disorders and maintaining a Patient Contact Registry.

Prader-Willi Syndrome Studies (
List of studies related to PWS; a service of the U.S. National Institutes of Health.

Authors & Reviewers

Last update/revision: December 2015
Current Authors and Reviewers:
Reviewer: Jennifer Goldman-Luthy, MD, MRP, FAAP

Page Bibliography

Butler MG.
Prader-Willi syndrome: current understanding of cause and diagnosis.
Am J Med Genet. 1990;35(3):319-32. PubMed abstract
Reviews of current understanding of the major clinical, cytogenetic, and DNA findings. Summarizes from literature clinical manifestations and cytogenetic abnormalities.

Safer, J.
The Normal One.
New York: Delta/Random House; 2002. 0-385-33756-6
Written by a psychotherapist and "normal" sibling of a child with special needs after many years of experience and research into the impact of children with special needs on typically developing siblings.