What Is Prader-Willi Syndrome (PWS)?

Prader-Willi syndrome affects 350,000 people worldwide.

Prader-Willi syndrome (PWS) is a rare genetic disorder characterized by chronic hunger, growth hormone deficiency, and behavior challenges.

Key features include:

  • Insatiable Hunger: A distinctive trait of PWS is an unending appetite. This, paired with a slowed metabolism, often leads to significant weight challenges.
  • Muscle & Growth: Individuals with Prader-Willi syndrome typically have weak muscle tone and less muscle mass. They also often grow to be shorter than average if they don’t receive the right treatment.
  • Cognitive Aspects: People with PWS can face learning disabilities, making everyday tasks a bit tougher.
  • Behavioral Challenges: People with Prader-Willi syndrome often face various behavioral challenges. These can include frequent temper tantrums, compulsive skin picking, stubbornness, and obsessive-compulsive behaviors. Managing these behaviors requires patience and understanding.

Understanding PWS is crucial for supporting those affected, enhancing their lives, and promoting inclusivity in society.

What is Prader Willi Syndrome

Symptoms & Characteristics of PWS

Early Life

Immediately after birth, the symptoms of Prader-Willi syndrome become noticeable. Infants often exhibit distinct physical and behavioral patterns.

  • Muscle Weakness: Decreased muscle tone, making infants appear “floppy.”
  • Feeding Difficulties: Trouble sucking or feeding, often requiring special assistance.
  • Distinct Facial Features: Almond-shaped eyes and a narrow bifrontal diameter.
An teenager with Prader Willi Syndrome
An toddler with Prader Willi Syndrome


The toddler and childhood years see a shift in PWS symptoms.
Key challenges emerge related to eating, learning, and behavior.

  • Insatiable Hunger: Beginning around age 8, leading to weight gain if not managed.
  • Learning Challenges: Mild to moderate intellectual impairment and delayed motor skills.
  • Behavioral Issues: Including temper tantrums, stubbornness, and compulsive behaviors.

Teenage Years

The teenage phase is challenging, especially for individuals with PWS. They have to navigate through typical growth issues unique to PWS.

  • Incomplete Puberty: Delayed or incomplete physical development, which can lead to short stature.
  • Social Struggles: Difficulty with peer relationships and social integration.
  • Ongoing Hunger: Preventing obesity is important for people with PWS.
An teenager with Prader Willi Syndrome
An adult male with Prader Willi Syndrome


As individuals with PWS transition from young adults into adulthood, they face a blend of health and social concerns. The emphasis is often on long-term health management and social integration.

  • Endocrine Issues: Challenges like diabetes or low sex hormone levels.
  • Orthopedic Problems: Scoliosis and osteoporosis may develop.
  • Mental Health Concerns: Risk of depression, anxiety, and other mood disorders.

Background & History of Prader-Willi Syndrome



Swiss doctors Andrea Prader, Alexis Labhart, and Heinrich Willi first identify PWS. They describe distinct symptoms like obesity and cognitive challenges in affected children.


Genetic Link

Researchers find a missing part on the 15th chromosome, confirming that PWS is a genetic disorder.


Advancements in Diagnosis

New genetic testing methods emerge, allowing for earlier and more precise diagnosis. This emphasizes the critical nature of early intervention.


Global Collaboration

Medical communities worldwide collaborate, sharing knowledge, improving treatments, and supporting individuals with PWS.


Advancements in Diagnosis

Innovative genetic testing methods are emerging, paving the way for earlier and more precise diagnoses. Also, many clinical trials are exploring new, proactive treatment strategies for individuals living with PWS.

Hope for the future

Prader-Willi Syndrome Clinical Trials

New trials for people with Prader-Willi syndrome show promise, giving hope to affected families and patients. This research breakthrough could lead to new treatments that greatly improve the lives of people with PWS.

The children of a family affected by Prader-Willi Syndrome

Frequently Asked Questions about PWS

Prader-Willi syndrome (PWS) is a variable and complex genetic disorder resulting from an abnormality on the 15th chromosome. It occurs in males and females equally and in all races. Prevalence estimates range from 1:15,000 to 1:25,000.

Experts believe that PWS is a multistage disorder characterized by decreased fetal movement during pregnancy and low birth weight. As toddlers get older, they start gaining more weight. If we don't limit their calories, this can lead to excessive eating (hyperphagia) and obesity.

Obesity, hypotonia, and hypothalamic dysfunction are the main medical problems related to Prader-Willi syndrome. Other factors may include adverse reactions to medications, high pain tolerance, gastrointestinal and respiratory issues, lack of vomiting, and unstable temperature. Adrenal insufficiency may also occur. The main problem for people with this condition is extreme hunger, which can cause dangerous obesity.

Abnormalities on chromosome 15 cause Prader-Willi Syndrome (PWS). This happens 3 different ways:

  1. Gene Deletion: In many cases, critical genes on a portion of the father's chromosome 15 are missing. This is the most common cause.
  2. Uniparental Disomy: The child has two copies of chromosome 15 from the mother instead of one from each parent.
  3. Imprinting Mutation: In less than 3% of cases, there is an imprinting mutation on the father's chromosome 15. The genetic material is there but remains inactive.

PWS varies from person to person but commonly affects the brain, particularly the hypothalamus. This leads to symptoms like:

  • Weak muscle tone (hypotonia) from birth.
  • Poor sucking in babies, causing feeding difficulties.
  • Swallowing problems with saliva and food.
  • Overeating (hyperphagia) due to the brain not signaling fullness, potentially causing severe obesity. This starts between 2-4 years old.
  • Short height if not treated with growth hormones.
  • Bone issues like hip dysplasia and osteoporosis.
  • Delayed sexual development.
  • Learning difficulties and developmental delays.
  • Frequent behavior problems.
  • Sensitivity to certain medications.
  • High pain tolerance, possibly missing injuries like fractures.
  • Digestive problems, including constipation and rare cases of stomach issues after binge eating.
  • Breathing problems during sleep, like sleep apnea.
  • Trouble regulating body temperature.

Doctors use unique genetic tests that analyze blood and saliva to identify PWS. These tests can be costly as they require specialized lab processing.

The best first test is DNA Methylation Testing, which detects over 99% of PWS cases and checks for all three genetic subtypes. The FISH test is useful but can't identify all subtypes, so it's not the preferred initial test. Chromosome Microarray testing is also effective, especially for detecting chromosome deletions and uniparental disomy (UPD).

Prader-Willi Syndrome (PWS) usually doesn't run in families. It happens because some genes on chromosome 15 aren't working right. This happens if a part of chromosome 15 from the father is missing. It can also occur when the child gets two chromosome 15s from the mother or if the genes from both parents aren't working right.

Scientists are always looking for new ways to treat the syndrome so children and adults can have a better quality of life. However, at this time there is no cure for Prader-Willi syndrome.

In 2000, the Federal Drug Administration approved Human Growth Hormone (HGH) for patients with Prader-Willi Syndrome (PWS). Studies show that HGH offers several benefits. It not only helps increase height and reduce body fat, but also boosts stamina and bone mineral density.

Many individuals with the syndrome participate in a variety of therapies, including physical, occupational, and speech therapies.

How PWSA | USA Supports the PWS Community

Stay up to Date with PWS News

Help Needed: Caregivers of Children with Prader-Willi Syndrome and Repetitive Verbal Behavior

Help Needed: Caregivers of Children with Prader-Willi Syndrome and Repetitive Verbal Behavior

Kasey Bedard, PhD, and her team at The Chicago School are seeking caregivers of children diagnosed with Prader-Willi Syndrome (PWS) who exhibit repetitive verbal behavior for a research study at The Chicago School. This study, part of a dissertation project, aims to test interventions that caregivers can implement at home. Study Details: – Duration: 2-3 […]

Fueling Hope: Aardvark Therapeutics’ $85M Boost Powers Breakthrough PWS Treatment

Fueling Hope: Aardvark Therapeutics’ $85M Boost Powers Breakthrough PWS Treatment

Aardvark Therapeutics has just hit a major milestone with an exciting $85 million Series C financing round! Led by Decheng Capital, with additional participation from several investors, including PWSA | USA, this funding is set to drive the development of ARD-101, a groundbreaking treatment for hyperphagia in Prader-Willi syndrome patients. ARD-101 showed promising early trial […]

Request for Prader-Willi Syndrome Research and Mini-Fellowship Grant Applications

Request for Prader-Willi Syndrome Research and Mini-Fellowship Grant Applications

PWSA | USA is currently seeking research project applications with direct impacts on individuals and families affected by PWS. We are offering mini-fellowship grants to support providers in enhancing their understanding of PWS through clinical proctorships. Research priorities include expanding knowledge about PWS, applying therapies, and attracting new providers and investigators to the field. Funding […]