Prader Willi Syndrome

What Is Prader-Willi Syndrome? Symptoms, Causes, Diagnosis, Treatment, and Prevention

Stephanie Watson
By Medically Reviewed by 
Reviewed:
Medically Reviewed
Prader-Willi syndrome is a rare genetic condition that starts in infancy and causes a variety of physical, mental, and behavioral changes. Most of the time it's caused when one section of a chromosome that's inherited from a person's father is missing.

Infants with Prader-Willi syndrome are tired and weak and have low muscle tone. They don't eat well, and as a result, they grow and develop slowly. Once they reach childhood, their appetite goes into overdrive. They eat and eat without ever feeling full. Overeating leads to many of the complications of the condition, including severe and sometimes life-threatening obesity and type 2 diabetes.

Prader-Willi causes distinctive features, such as almond-shaped eyes, short height, small hands and feet, and light hair. It's common for children with this condition to have delayed puberty and learning and intellectual disabilities.

They also can have behavioral problems such as temper tantrums, obsessive-compulsive issues, and skin picking.

People with Prader-Willi syndrome will need lifelong treatment from a team of specialists that includes a primary care provider, an endocrinologist, and physical, occupational, and speech therapists. Although this condition isn’t curable, getting the right care early can lead to a better quality of life.

Signs and Symptoms of Prader-Willi Syndrome

Symptoms vary from person to person. Some symptoms are mild while others are severe. It's important for parents to talk with a doctor and genetic specialist about the outlook and appropriate treatment for their child.

Most infants with Prader-Willi syndrome have reduced muscle tone, called hypotonia.

This symptom can start before birth. The fetus may move less than usual in the womb or end up in a breech position, which may require the use of instruments in delivery. After birth, those weak muscles may make the baby feel "floppy," similar to holding a rag doll.

Babies with Prader-Willi syndrome have distinctive facial features, including:

  • A long and narrow head and forehead
  • Almond-shaped eyes
  • A turned-down mouth with a thin upper lip
  • A thin bridge of the nose

A few other symptoms are characteristic of this condition:

Poor Growth Infants with Prader-Willi syndrome are tired and sluggish, with a weak cry. They may not respond well to stimulation. Their weak muscles make it hard for them to suck firmly enough to breastfeed or bottle feed. This can lead to failure to thrive. Some babies will need to be tube fed.

The hypotonia and feeding problems should improve as babies get older. Once they begin to eat better, they will start to grow.

Food Cravings Within a few years, children’s feeding issues change completely. They develop an insatiable appetite. Because they don’t feel satisfied after eating, and they have weak muscles and a lower metabolism, these children gain an excessive amount of weight. To satisfy their food cravings, children may resort to hoarding or hiding food.

Without food restriction by a parent or other caregiver, children can become morbidly obese, which can contribute to diabetes, heart problems, and other serious complications.

Intellectual and Motor Skills Delays Children with Prader-Willi syndrome often have developmental delays and intellectual disabilities that vary in severity. These children are typically slower than their peers to reach milestones like walking and crawling. They may be slow to speak, and struggle to speak clearly well into adulthood. And they may have difficulty thinking and reasoning.

Slowed Sexual Development Prader-Willi syndrome also affects children's sex organs.

The sex glands called gonads produce little to none of the hormones that normally help the sex organs develop. The name for this is hypogonadism.
Children who are assigned male at birth may have a small penis and scrotum. One or both of their testes may not have descended from the belly, which is called cryptorchidism. Men may not grow facial hair or develop a deeper voice.

In those identified as female at birth, the clitoris and labia are typically smaller than usual. Puberty often starts late. Some girls with Prader-Willi syndrome don't get their first period until age 30, or ever. As a result of these changes, people with this condition may not be able to have children.

Behavior Problems Children with Prader-Willi can be angry or stubborn. They can throw temper tantrums, especially when they are denied the food they crave.

Some children develop obsessive-compulsive or repetitive behaviors. Skin picking is also common. A small number of people with Prader-Willi syndrome develop psychosis — a severe mental health condition that causes them to see, hear, or believe things that aren’t real.

Sleep Disorders Difficulty sleeping is another symptom of Prader-Willi syndrome. Some children and adults have the sleep disorder, sleep apnea, which causes repeated pauses in breathing throughout the night. Sleep problems can lead to daytime sleepiness and added behavioral problems.

Prader-Willi syndrome causes a variety of other symptoms, including:

Causes and Risk Factors of Prader-Willi Syndrome

Prader-Willi syndrome is a genetic condition, meaning that it is caused by a mistake in a group of genes. Chromosomes are the strands of DNA in each of our body's cells. They carry the genetic information needed for our bodies to develop and function.

Prader-Willi syndrome happens when a group of genes on chromosome 15 are missing or not working. The condition has three subtypes, each with a different genetic cause:

Deletion Babies normally inherit one copy of a chromosome from each parent. In about two-thirds of people with Prader-Willi syndrome, the copy of chromosome 15 that is inherited from the father is missing a section of important genes. This mistake usually happens randomly as the baby develops. It isn't inherited.

Uniparental Disomy Less often, the entire chromosome 15 from the father is missing. Instead, the baby has two copies of chromosome 15 from the mother.

Imprinting Defect A very small percentage of cases happen from an imprinting problem. Imprinting means that the ability of the gene to be turned on depends on which parent it came from. In this case, the genes on chromosome 15 from the father are there, but they're "turned off" or silenced.

The missing or inactive genes lead to the symptoms of Prader-Willi syndrome. For example, the OCA2 gene holds the instructions to make the pigment melanin, which gives the skin and eyes their color.

Not having this gene causes the light skin, hair, and eyes of Prader-Willi syndrome.

How Is Prader-Willi Syndrome Diagnosed?

Newborns with hypotonia and poor sucking ability should get tested for Prader-Willi syndrome. The process starts with a medical history and an exam to look for the classic symptoms.

The only way to confirm the diagnosis is with genetic tests to find the deleted sections of chromosome.

About 99 percent of people with Prader-Willi syndrome can be diagnosed with a DNA methylation test, which screens for many different genetic changes.

If this test suggests Prader-Willi syndrome, a FISH test (fluorescence in situ hybridization) to map the genes may be done to determine the subtype. Other chromosome studies can help to confirm the cause.

Prognosis of Prader-Willi Syndrome

Type 2 diabetes, heart failure, and other complications of morbid obesity can shorten the lives of people with Prader-Willi syndrome.

With the right treatment, they can live as long as their peers.

Yet they will need a lot of support from their families and a variety of professionals to remain independent and have a good quality of life.

Those with more severe intellectual disabilities may need to live in a supervised group home. And most people with this condition will need constant diet supervision to prevent overeating and weight gain. 

Duration of Prader-Willi Syndrome

Although there are treatments to manage the symptoms of Prader-Willi syndrome, right now there is no cure. This is a lifelong condition.

Treatment and Medication Options for Prader-Willi Syndrome

Treatments for Prader-Willi syndrome manage the symptoms. Being treated early and continuing therapies can lead to a better quality of life. Because this condition affects so many parts of the body, the treatment team includes a variety of specialists, including a:

Medication Options

Babies with hypogonadism can be treated with the sex hormone testosterone (boys) or estrogen (girls) to help their genitals grow to their normal size and to improve bone strength.

However, testosterone can sometimes worsen behavioral problems in boys.

Human growth hormone is approved to treat Prader-Willi syndrome. This hormone has several effects on a child’s growth. It:

  • Increases height
  • Reduces body fat
  • Reduces the signs of Prader-Willi syndrome on the face
  • Improves breathing
  • Increases bone mineral density
  • Increases energy levels
  • Reduces behavioral problems

Children can start on growth hormone treatment as early as age two to three months. The sooner they start, the more hormonal treatment helps. Adults may continue to take growth hormone, but at a lower dose.

Antidepressants called selective serotonin reuptake inhibitors (SSRIs) may be helpful for the behavioral and emotional symptoms of Prader-Willi syndrome.

Because these medicines cause side effects, they may not be recommended for children under 18. People with psychosis may need to take antipsychotic medication.
Skin picking can cause infections such as cellulitis, which requires antibiotic treatment. Keeping affected areas of skin covered in antibiotic cream may help to prevent future infections.

Other Treatments

Children with Prader-Willi syndrome will need a variety of therapies to improve their motor and intellectual skills and manage behavioral issues. They may receive:

  • Physical therapy
  • Occupational therapy
  • Speech therapy
  • Special education
  • Behavioral therapy
Cognitive behavioral therapy (CBT) helps to identify and change harmful behaviors. This type of therapy can be helpful for managing skin picking and other behavioral problems associated with Prader-Willi syndrome.

Structure and routines in daily life are important to give children clear expectations.

Carefully monitoring and restricting food access can help prevent rapid and extreme weight gain.

Surgery

Infants who have trouble breastfeeding or bottle feeding may need a procedure called gavage. A thin tube is placed down through the baby's nose and mouth into the stomach to provide nutrition.

Surgery is typically done to fix undescended testicles, because without treatment, this problem can increase the risk for testicular cancer. The surgery is usually performed by age 2 or 3.

Bariatric surgery isn’t recommended for people with Prader-Willi syndrome. They often can’t stick to the strict diet needed to maintain weight loss after surgery.

Alternative and Complementary Therapies

Children with Prader-Willi syndrome need to eat a carefully controlled diet, with small portions and an emphasis on fruits and vegetables instead of carbs.

They may need a vitamin supplement to ensure they get proper nutrition. Because the urge to eat is so strong, parents may need to lock the refrigerator and cabinets to prevent children from stealing food.
Exercise is an important complement to diet.

Because children with Prader-Willi have reduced endurance and muscle tone, breaking exercise into 5- or 10-minute sessions throughout the day can be helpful.

Prevention of Prader-Willi Syndrome

There is no way to prevent Prader-Willi syndrome because it is a genetic condition. However, it is possible to prevent its complications with medication and behavioral interventions started early in the child’s life.

If you have a child with Prader-Willi syndrome and you would like to have another child, a genetic counselor can help you determine your risk of this condition in another pregnancy.

Complications of Prader-Willi Syndrome

Many of the complications from Prader-Willi syndrome are due to excess weight gain, including:

Other complications stem from problems with hormone production. These include:

  • Infertility or sterility
  • Osteoporosis
Behavioral and intellectual problems can reduce a person’s quality of life. Therapy and other interventions are important to help manage these issues.

Research and Statistics: Who Has Prader-Willi Syndrome?

Between 1 in 10,000 and 1 in 30,000 people have Prader-Willi syndrome.

The prevalence varies from country to country. For example, between 1 in 16,062 and 1 in 25,000 Americans have Prader-Willi syndrome. In Australia, the rate is 1 in 15,830 people.

An estimated 350,000 to 400,000 people have the condition worldwide. About 20,000 of them live in the United States.

Prader-Willi syndrome affects males and females equally. People of all races and ethnicities can get this condition.

BIPOC and Prader-Willi Syndrome

Prader-Willi syndrome affects people of all races, but it might show up differently in people of color. One study done in the late 1990s found different physical characteristics in African Americans with the condition.

Black Americans in the study were less likely to have growth problems. Their hands and feet were of normal size, and their facial features didn’t fit the norm for Prader-Willi. The authors said these differences might make it harder to diagnose Prader-Willi syndrome in Black people.

Related Conditions

Prader-Willi syndrome is similar to a few other genetic disorders, including:

  • Albright hereditary osteodystrophy
  • Alstrom syndrome
  • Angelman syndrome
  • Bardet-Biedl Cohen syndrome
  • Borjeson-Forssman-Lehmann syndrome
  • Congenital muscular dystrophy
  • Fragile X syndrome
  • Spinal muscular dystrophy

Resources

Community and Support

Foundation for Prader-Willi Research

This organization is working to develop new treatments to improve the outlook for people with Prader-Willi syndrome. The Foundation also hosts advocacy events and research symposiums.

International Prader-Willi Syndrome Organisation

On this global organization’s website, you can find the support you need to manage Prader-Willi syndrome, from free diagnosis to advice from parents and professionals.

Prader-Willi Syndrome Association (PSWA)

Families of those diagnosed with Prader-Willi syndrome can turn to this organization for support and education. PWSA also sponsors researchers and promotes advocacy efforts.

Reliable Sources of Prader-Willi Syndrome Information

Eunice Kennedy Shriver National Institute of Child Health and Human Development

This website comes from one of the government agencies that’s working to better understand Prader-Willi syndrome. It includes information on the causes, symptoms, and treatments, as well as a searchable guide to ongoing clinical studies.

Genetic and Rare Diseases Information Center

This website from the National Institutes of Health offers a good overview of the condition, which you can either read or listen to.

Mayo Clinic

This trusted source of medical information provides a basic overview of Prader-Willi syndrome, including a list of questions to ask your doctor.

National Organization for Rare Disorders

Learn the symptoms, causes, and treatments for Prader-Willi syndrome, along with a list of helpful resources.

Editorial Sources and Fact-Checking

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Editorial Sources and Fact-Checking

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