What is Prader-Willi Syndrome (PWS)?

What is Prader-Willi Syndrome (PWS)?

Prader-Willi syndrome is a rare genetic disorder that affects an estimated one in 10,000 to 30,000 births. It affects many body parts as children grow and develop, and symptoms include poor muscle tone and short stature.

Children with Prader-Willi syndrome also develop insatiable hunger and can’t feel full. Overeating due to this excessive appetite can lead to life-threatening obesity. Because of these and other symptoms, most people with Prader-Willi syndrome need specialized care.

Stages of Prader-Willi Syndrome


Prader-Willi syndrome varies according to the timing and severity of symptoms. Some of the most troublesome symptoms of Prader-Willi syndrome have to do with eating, appetite and obesity.

These progress gradually, in phases:

  • Prenatal signs. Decreased movement of the fetus and low birth weight compared to siblings.
  • Birth to about two years. As part of poor muscle tone, the baby has difficulty sucking and may fail to gain weight appropriately. Feeding and growth improve after about 9 months of age.
  • Age 2 to about 4-8 years. At first, weight and calories eaten are average, then appetite and interest in food increase; the child can feel full after eating.
  • Age about 4-8 years to adulthood. A constant feeling of hunger sets in. The inability to feel full leads to frequent eating, large portions, and rapid weight gain to the point of obesity if not managed.
  • Adulthood. Individuals may develop the ability to feel full and better manage their eating behavior.

Signs & Symptoms of Prader-Willi Syndrome


Prader-Willi syndrome is a lifelong condition with different symptoms and increased risk of complications over time. Symptoms and their severity vary from one person to another. Pediatric specialists at NewYork-Presbyterian are experienced in treating the symptoms of Prader-Willi syndrome.


  • Poor muscle tone; baby feels floppy, like a rag doll
  • Poor response to stimulation, lethargy or tired, weak cry
  • Trouble sucking and may need a special bottle nipple or a feeding tube
  • Distinctive facial features, including almond-shaped eyes, thin upper lip, downturned mouth, narrow forehead, and long, narrow head
  • Underdeveloped genitals and undescended testicles in boys

Early childhood and beyond

  • Overwhelming hunger, and inability to feel full, that can lead to life-threatening obesity
  • Mild to moderate cognitive and learning issues
  • Delayed motor and language development
  • Behavioral issues, including temper tantrums, stubbornness, obsessive/compulsive behavior
  • Short stature
  • Small hands and feet
  • Curvature of the spine (scoliosis)
  • Susceptibility to bone fractures
  • Sleep problems
  • Underdeveloped genitals
  • High pain tolerance
  • Gastrointestinal issues
  • Difficulty regulating body temperature


What Causes Prader-Willi Syndrome?


Prader-Willi syndrome is caused when genes on chromosome 15 are missing or not working properly. These genes are involved in how the brain regulates certain hormones. Disruptions in hormones cause many symptoms of Prader-Willi syndrome.

Every person has two copies of chromosome 15, one inherited from their mother and the other from their father. Prader-Willi syndrome happens when there is a problem with the copy of chromosome 15 that came from the affected person’s father. It could be that the genes are missing or that the genes don’t work. In other cases, a person inherits two copies of chromosome 15 from their mother and no copy from their father.



The insatiable hunger felt by people with Prader-Willi syndrome leads to overeating and obesity, that is sometimes life-threatening.

Prader-Willi syndrome complications include:

Additional complications of Prader-Willi syndrome include:

  • Infertility, meaning that most people with Prader-Willi syndrome, both men and women, are not able to have children
  • Breathing problems, including sleep apnea, chest infections, and narrowed airways
  • Osteoporosis, which causes bones to become brittle and more susceptible to fractures
  • High pain tolerance that prevents the detection of fractures or of stomach pain after binge eating
  • Behavioral issues that interfere with family relationships, education, and social adjustment and reduce the quality of life



There is no known way to prevent Prader-Willi syndrome. The genetic changes that cause the disorder to happen randomly and are not passed down from parent to child. For couples who have a child with Prader-Willi syndrome, a genetic counselor may be able to help determine the risk of having a second child with the disorder through genetic testing. This risk depends on the genetic cause of Prader-Willi syndrome in the first child.

Get Care

Trust NewYork-Presbyterian for Prader-Willi Syndrome Care

If your child has symptoms of Prader-Willi syndrome, or a diagnosis, schedule an appointment for a consultation with one of NewYork-Presbyterian’s experienced pediatricians.

At NewYork-Presbyterian our patients have access to a team of pediatric specialists who can provide compassionate care for the symptoms and complications of Prader-Willi syndrome. Early treatment is the best way to ensure a good quality of life for children with Prader-Willi syndrome.