Prader-Willi syndrome is a genetic disorder caused by changes to chromosome 15. It affects growth, behavior, and learning and requires continual management to avoid potentially life threatening complications.

Prader-Willi syndrome (PWS) is a rare genetic syndrome marked by low muscle tone, below average growth in infancy, excessive appetite, and low muscle mass in adulthood. First identified in the 1950s by the Swiss physicians Andrea Prader and Heinrich Willi, PWS affects just 1 in 10,000–30,000 people, or 350,000–400,000 people, worldwide.

Here’s what you need to know about PWS, what causes it, and what treatments may help.

PWS is a genetic syndrome that usually occurs at random or, in some people, may be inherited. It’s caused by changes or deletions to a portion of chromosome 15. Researchers have found that PWS is a complex, multisystem disorder because it affects various systems throughout the body.

A major symptom of the syndrome is that people may not feel full, regardless of their diet. This situation may lead to excessive eating, morbid obesity, and related complications like heart disease, sleep apnea, and diabetes that can be life threatening.

No two people with PWS experience the same symptoms that start at the same time. For many, PWS is present at birth, typically with notable hypotonia (reduced muscle tone or floppy) and difficulty using muscles.

Other symptoms in infants may include:

  • classic physical characteristics, such as:
    • almond-shaped eyes
    • narrow forehead and bridge of the nose
    • thin upper lip
    • small hands and feet
  • feeding difficulties due to a weakened sucking reflex
  • lethargy or low level of alertness
  • changes of the genitals, such as undescended testicles or smaller than the average size of the following:
    • penis
    • testicles
    • clitoris
    • labia

As a child grows into an adult, other physical symptoms may develop:

Additional symptoms may include:

Language matters

In this article, we use “biological mother” and “biological father” to differentiate between the chromosomal contribution of the birthing parent and the nonbirthing parent.

Although we typically avoid language like this, specificity is key when reporting on research participants and clinical findings.

Unfortunately, the studies and surveys referenced in this article didn’t report data for or may not have had participants who are transgender, nonbinary, gender nonconforming, genderqueer, agender, or genderless.

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PWS is caused by changes to chromosome 15 in a portion of the gene called the “Prader-Willi critical region” (PWCR). The changes affect the way this gene turns on and off, which is what eventually leads to the symptoms of the disorder.

PWS isn’t inherited but rather is caused by mutations that cause deletions or partial deletions on chromosome 15 during conception.

A “deletion” in a chromosome means that the section of chromosome is missing. According to the National Institute of Child Health and Human Development, in individuals with PWS, the deletion most often occurs on the biological father’s chromosome 15. The biological mother’s chromosome 15 is inactive and can’t supply the missing genetic information.

Other genetic changes that may lead to PWS include uniparental disomy and imprinting center defect.

Most often in PWS, “uniparental disomy” means that a child inherits 2 copies of chromosome 15 from the biological mother and none from the biological father. The genes inherited from the mother in the PWCR are inactive.

Having an “imprinting center defect” means that the copy of chromosome 15 from the biological father is unable to be read, so it’s inactive.

While PWS is a genetic condition, it isn’t always inherited from parents during conception. Instead, it usually occurs randomly after conception, at which point parts of chromosome 15 change or are deleted.

As a result, there aren’t necessarily any specific risk factors. That said, if you have one child with PWS and are considering another pregnancy, you may consult with a genetic counselor to go over the risks.

Diagnosis may begin by observing the signs — specific physical characteristics and muscular or feeding difficulties — at or around birth. If a doctor suspects PWS, genetic testing via a blood test can confirm whether your child has the syndrome.

Experts share that genetic testing can diagnose nearly all instances of PWS in babies.

There’s no cure for PWS. Early diagnosis and appropriate support strategies may help address symptoms and avoid complications. In general, treatment is supportive and aimed to address the specific symptoms a person is experiencing.

Support for babies and children revolves around addressing growth and physical, behavioral, and psychological development.

Your child may need:

  • feeding support to meet nutritional needs and ease of feeding, such as:
    • special bottle nipples
    • high calorie formula
    • tube feeding (also called “gavage feeding”)
  • human growth hormone treatment to promote the following:
    • overall growth
    • reduced body fat
    • increased muscle tone
    • strengthened respiratory system
  • sex hormone treatment with testosterone (for babies assigned male at birth) and estrogen/progesterone (for babies assigned female at birth) to encourage the testes to descend and the onset of puberty
  • diet and exercise supervision to avoid having obesity
  • caregiver support and education
  • language and speech therapy
  • physical and occupational therapy
  • mental health support
  • treatment for any other related conditions, like:

Without treatment, complications of PWS may include below average weight gain in infancy, short stature after puberty, and having obesity.

Supportive strategies don’t end in childhood. Many adults with PWS will need specialized care and may move into residential facilities for people with similar conditions. Some people with PWS may also be able to hold jobs in supportive environments.

The focus for supportive strategies in adulthood shifts to behavioral issues like weight management to help avoid having obesity and obesity-related diseases and continued treatment with growth hormone for muscle mass upkeep. With the advances in care of individuals with PWS, the mortality rate has decreased by about 1.25% per year.

What is the life expectancy of a person with Prader-Willi syndrome?

The median age of death for a person with PWS is 30 years of age, but life expectancy ranges between 1 month and 58 years.

What are two main symptoms of Prader-Willi syndrome?

The primary symptoms of PWS include increased appetite and weight gain as well as difficulties with muscle control and weakness.

What is the physical appearance of a child with Prader-Willi syndrome?

Physical characteristics of PWS may include almond-shaped eyes, a narrow forehead and bridge of nose, a thin upper lip, and small hands and feet.

PWS is a rare genetic disorder that affects a person from birth through the rest of their lives. Appropriate support can address symptoms, prevent complications, and improve a person’s overall quality of life. While support may be ongoing, people with PWS can live well into adulthood.