What Is Prader-Willi Syndrome?

Prader-Willi syndrome (PWS) is a rare, complicated condition that affects many parts of your body. It stems from a problem with one of your chromosomes (a strand of DNA that carries your genes). It can cause physical issues, like extreme hunger and weak muscles, as well as learning and behavioral problems.

Only about 1 in 10,000 to 30,000 people in the world have PWS.


PWS usually happens because of a problem with your genes. In most cases, doctors don't know what causes it, but about 2% of people with PWS have it because they didn't get the right copies of a certain chromosome from their parents.

There's no way to prevent it. But if you plan to have a baby, you and your partner can be screened for PWS risk.

A head or brain injury can also cause the syndrome.

Signs and Symptoms

A baby may show signs of PWS early on. He may have almond-shaped eyes, his head may get narrow at the temples, his mouth might turn down at the corners, and he might have a thin upper lip.

He also may have these symptoms:

  • Poor muscle tone or limbs that hang loosely when you hold him
  • Inability to suck or nurse well, so he gains weight slowly
  • Eyes that cross or wander
  • Appearance of being tired all the time
  • Weak or soft cry
  • Poor response to you

In early childhood, kids with PWS start to show other signs. It affects a part of their brain called the hypothalamus -- this is what tells you you're full when you eat enough food. People with PWS don't get the feeling of being full, so the most common signs are nonstop hunger and weight gain.

A child with PWS may always want more food, eat big portions, or try to hide or store food to eat later. Some kids even eat food that's still frozen or in the garbage.

Your child may also:

  • Be short for her age
  • Have small hands or feet
  • Have extra body fat and not enough muscle mass
  • Have sex organs that may not develop
  • Have mild to moderate learning problems
  • Be slow to learn to talk, sit, stand, or walk
  • Have temper tantrums
  • Pick at her skin
  • Have sleep problems
  • Have scoliosis -- a curved spine
  • Have too little thyroid or growth hormones


These signs of PWS are less common, but some people have them:

  • Vision problems, like being nearsighted
  • Lighter skin and hair color than the rest of the family
  • High tolerance for pain
  • Inability to keep body temperature under control during a fever or in a hot or cold place
  • Thick saliva that can cause tooth decay or other problems
  • Osteoporosis, or thin, weak bones that break easily

Because their sex organs don't develop, women with PWS may never get a period. Or they may start their periods much later than others. Men who have PWS may not have facial hair. They may have small sex organs, and their voices may not change in puberty. People who have PWS usually aren't able to have children.


Your doctor can usually diagnose PWS with a blood test called methylation analysis. This shows if there's a problem with the gene that can cause PWS.


There's no cure, but if you have a child with PWS, you can help her stay at a healthy weight, have a good quality of life, and prevent health problems down the road. Her treatment will depend on the symptoms.

  • Babies: High-calorie formula may help an infant stay at a healthy weight if he can't eat well because of weak muscle tone. You also can use special nipples or a Gavage feeding tube, which puts breast milk or formula directly in your baby's stomach, to make sure he gets enough food.
  • Older kids and teens: Set clear limits on how and when your child eats to avoid too much weight gain. A low-calorie, balanced diet and lots of exercise can help him stay at a healthy weight. Some kids with PWS may need to take extra vitamin D or calcium.

If your child tries to grab and hide food, you might lock cabinets, the pantry, or the refrigerator.

For teens with PWS, hormones like testosterone, estrogen, or human growth hormone (HGH) may help with small stature, poor muscle tone, or extra body fat. Hormone replacement may build stronger bones and prevent osteoporosis later on.


Antidepressants, like selective serotonin reuptake inhibitors (SSRIs), may help ease behavior problems caused by PWS.

Therapy may also help your child deal with sleep apnea, mood or speech problems, or trouble with schoolwork.

Kids with PWS should get regular eye exams to check for vision problems. Your child's doctor should screen for scoliosis, hip dysplasia, or thyroid problems.

The Prader-Willi Syndrome Association has online support groups and tips for parents.

WebMD Medical Reference Reviewed by Dan Brennan, MD on March 02, 2019



Foundation for Prader-Willi Research.

Genetics Home Reference: "Prader-Willi Syndrome."

Mayo Clinic: "Prader-Willi Syndrome."

National Organization for Rare Disorders: "Prader Willi Syndrome."

Prader-Willi Syndrome Association.

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