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The following guide is designed to be a primer for individuals seeking information about Prader-Willi Syndrome (PWS). We have tried to be as objective as possible in presenting the most accurate information available, but it is the responsibility of each individual to conduct their own research beyond this guide. If there is information that we have missed out or are as yet unaware of, please let us know by emailing contact@qunomedical.com.

What is Prader-Willi Syndrome?

Prader-Willi Syndrome (also known as: PWS, Prader-Labhart-Willi Syndrome, Willi-Prader Syndrome) is a complex genetic disorder that affects appetite, growth, metabolism, behavior, and cognitive function throughout an affected individual's life. The condition is characterized by low muscle tone in infancy, an uncontrollable hunger, stunted growth, incomplete sexual development, and mild to moderate intellectual impairment.

PWS occurs in 1 in 10,000 to 1 in 30,000 people worldwide, with no correlation to gender, race, or ethnicity. More than 400,000 people around the world live with PWS.

What causes Prader-Willi Syndrome?

PWS is not typically inherited and there are no known risk factors so parents who have a child with PWS have less than a 1% chance of having a second child with the condition. PWS occurs when genetic changes happen during the formation of the egg or sperm or in early fetal development. More specifically, the condition is caused by an error in one or more genes in a particular region of chromosome 15. PWS occurs for one of these reasons:

  • The father’s genes on chromosome 15 are missing

  • An error or defect is present in the father’s genes on chromosome 15

  • Two copies of chromosome 15 from the mother and no chromosome from the father were inherited

It’s thought that the defect on chromosome 15 interferes with the normal functions of a portion of the brain called the hypothalamus which regulates hunger and thirst, and produces hormones responsible for growth and sexual development.

How is Prader-Willi Syndrome diagnosed?

If your physician suspects that your baby has PWS the diagnosis can be confirmed by genetic testing. Methylation Analysis - which detects over 99% of cases including all of the major genetic subtypes of PWS - is the preferred method of testing, however, it is not available everywhere. A Fluorescent In- Situ Hybridization (FISH) test can identify individuals who have PWS as a result of a deleted gene. FISH tests will not identify those who have PWS caused by an imprinting error, nor as a result of inheriting two copies of a chromosome from the same parent, instead of one copy coming from each parent (uniparental disomy). PWS caused by uniparental disomy can be diagnosed with a Polymerase Chain Reaction (PCR) test. There are a number of symptoms which indicate the disorder so the earlier it is identified the better it can be managed.

What are the symptoms of Prader-Willi Syndrome?

There are many symptoms which indicate PWS, however, not everyone with the disorder will experience all of them. The following signs and symptoms generally occur in several phases, while some may be present at birth or while the baby is still in the womb, others appear during early childhood but remain throughout life and require careful management or treatment.

Symptoms in the Uterus

  • Reduced fetal movement

  • Frequently abnormal fetal position

  • Occasional polyhydramnios or excessive amniotic fluid

  • Breech or caesarean births are common due to an abnormal fetal position at delivery because of decreased fetal movement

Symptoms in newborns

  • Lethargy and poor responsiveness: Babies may seem unusually tired, respond poorly to stimulation, have difficulty waking up or have a weak cry.

  • Poor muscle tone: Babies with PWS are abnormally limp and can feel like rag dolls when held due to a condition called hypotonia or floppy baby syndrome. They may rest with their elbows and knees loosely extended and have difficulty maintaining flexed ligaments. Babies with hypotonia often have difficulty feeding as they have a poor sucking reflex due to poor muscle tone. This in turn can make it hard for them to gain weight.

  • Difficulties establishing respiration.

  • Male infants may have undescended testicles.

Physical features of Prader-Willi Syndrome

Children may be born with distinct physical features including:

  • Almond-shaped eyes

  • A narrowing of the head at the temples

  • A downturned mouth and a thin upper lip

  • Small hands and feet in comparison to the rest of their body

  • Short stature as a result of stunted growth

  • Underdeveloped sex organs (hypogonadism)

  • Light skin and hair compared with other family members

  • Soft skin which bruises easily

  • Lack of eye coordination (strabismus). The eyes may not move together — they may cross or wander to the side.

Symptoms in early childhood to adulthood

  • Delayed motor development: This affects 90% to 100% of children with PWS. Toddlers with Prader-Willi syndrome often take twice as long as other children to reach early milestones in physical movement, such as sitting up or walking.

  • Speech problems: Speech is often delayed. Poor articulation of words may be an ongoing problem into adulthood.

  • Apraxia: Many children with PWS have a motor disorder which makes planning and coordinating movements difficult. In addition to impairing the individual’s ability to plan the movements needed to speak, apraxia may also make it hard for them to perform many other movements, and can affect their ability to perform activities such as writing, typing, riding a bike, and playing.

  • Food cravings and obesity: A hallmark of PWS is a chronic feeling of insatiable hunger combined with a slowed metabolism which can lead to excessive eating, rapid weight gain, and morbid obesity. The constant feeling of ravenous hunger (also called hyperphagia) usually begins around age two and persists for the rest of the patient’s life. If food intake isn't controlled affected individuals can eat themselves to death. PWS is the most common genetic cause of obesity that has been identified. Individuals with PWS need to have their access to food strictly controlled by someone else; this could include having food locked away in order for them to maintain a normal weight.

  • Scoliosis: Many children with PWS have an abnormal curvature of the spine.

  • Underdeveloped sex organs: Another hallmark of PWS is a condition called hypogonadism in which the sex organs — testes in men and ovaries in women — produce few or no sex hormones. As the sex hormones, testosterone and estrogen, play an important role in sexual development, individuals with hypogonadism experience incomplete development at puberty and partial to complete infertility. Women with hypogonadism may not start menstruating until their 30s if at all, and men may not have much facial hair, and their voices may never fully deepen.

  • Poor growth and physical development: Children with PWS have a high body fat to low muscle mass ratio and without treatment they usually grow up to be shorter than their family members. They may have small hands, feet and genitals.

  • Intellectual disabilty: The vast majority of individuals with PWS have mild to moderate cognitive impairment. It’s common for them to have difficulties when thinking, reasoning, and problem-solving but they are generally good at reading and completing puzzles, and have good visual processing skills relative to their poor auditory processing abilities. Even those without significant intellectual disability have some learning disabilities. There are, however, a handful of cases of people with PWS with average intelligence. Although people with PWS have poor short-term memory skills they have excellent long-term memory skills.

  • Behavioral problems: Temper tantrums, stubbornness, anger, and controlling or manipulative behavior is commonly exhibited in both children and adults with PWS. Obsessive or repetitive behaviors and other mental health disorders, such as Obsessive Compulsive Disorder and skin picking, may develop. People with PWS, however, tend to be very friendly, loving, forgiving, and caring (particularly with babies and animals).

  • Sleep disorders: Many children and adults experience disruptions of their normal sleep cycle and sleep apnea, a condition in which breathing pauses during sleep. These disorders can increase lethargy and contribute to behavioral problems. Obesity may worsen sleep disorders.

  • Endocrine problems: Some with PWS suffer from other endocrine problems including hypothyroidism in which there is insufficient production of thyroid hormone, growth hormone deficiency or central adrenal insufficiency, which prevents the body from responding appropriately during stress or infections.

What treatment is available to individuals with Prader-Willi Syndrome?

Unfortunately there is no cure for PWS. There are, however, treatments which may improve the overall health and quality of life of individuals with the condition, particularly if carried out early. Treatments should focus on the specific symptoms affecting each individual with the disorder. An effective program can be designed by a team of specialists who may include clinical geneticists, pediatricians, orthopedists, endocrinologists, speech therapists, psychologists, dieticians, nutritionists, and other healthcare professionals. The following treatments or therapies have been found to be effective in managing some of the symptoms of PWS and can reduce the risk of complications.

  • Feeding tubes can help newborns with poor sucking reflex.

  • Strict food supervision starting around the age of three combined with an exercise program can ease children with the disorder into a healthy lifestyle. Obesity is the greatest threat to the affected individual’s health as it can lead to cardiac diseases, joint problems, lung problems, sleep apnea, type 2 diabetes, and other serious conditions which can be life-threatening if not controlled. Working with dieticians and nutrionists to design a healthy diet, and preventing access to food when a patient is young enough will make it easier for them to maintain a healthy weight. Establishing a regular exercise routine will improve muscle tone and contribute to weight loss.

  • Growth hormone therapy can increase height, bone density and stamina, increase muscle mass, decrease body fat, build strength and agility, and improve weight distribution. One side-effect of growth hormone therapy, however, is that it can lead to sleep apnea.

  • Hormone replacement therapy can counter the effects of hypogonadism.

  • Mental health and behavioral counselling as well as medication may help to treat some behavioral issues. These therapies can help with issues like skin picking and Obsessive Compulsive Disorder. Group homes are often necessary in adulthood.

  • As a lot of their behavior is driven by anxiety, routines are extremely important for someone with PWS. Many people with PWS find transitions difficult to cope with, so having routines in place can help ease them into any changes.

  • It’s crucial that children with PWS receive speech, physical, and occupational therapy as early as possible.

What educational options are available to individuals with Prader-Willi Syndrome?

The right education for the child’s IQ level is essential. As children with PWS vary considerably in their cognitive abilities, ranging from severe learning disabilities through to mild or no learning disabilities, it is important to remember that a school that is right for one child with PWS may not be right for another. Depending on their ability and the amount of support provided, children may attend mainstream or special schools. Typically professionals already involved with your child will be able to advise you on procedures in your area, you can however, contact a child development center, local authority or city council to request an assessment. If you decide your child should attend a mainstream school or nursery, you will have to research the possibilities to ensure that they can manage your child’s dietary needs. Some will already have a healthy-eating policy in place, but if not they might be willing to adopt one. Few adults with PWS are employed full-time, but many find part-time or voluntary work, or educational courses very fulfilling.

Where can I learn about treatment options for Prader-Willi Syndrome?

The following links will provide valuable information for those looking for PWS treatment options:


International Prader Willi Syndrome Organization

Genetic and Rare Diseases (GARD) Information Center


Prader-Willi Syndrome Association (UK)

Prader-Willi Association France

North America

NIH/National Institute of Child Health and Human Development (U.S.A.)

Medical Home Portal (U.S.A.)

Foundation for Prader-Willi Research (U.S.A.)

Foundation for Prader-Willi Research Canada

Prader-Willi Syndrome Association (U.S.A.)

March of Dimes Birth Defects Foundation (U.S.A.)

The Children's Institute of Pittsburgh (U.S.A.)


Prader-Willi Research Foundation Australia

Prader-Willi Syndrome Association Australia


The information in this article is for educational purposes only and does not replace medical advice. Always consult your doctor before starting any treatments.

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