Skip to main content


Prader-Willi Syndrome (PWS)


PWS is a rare genetic disorder of chromosome 15. Children and adults affected by PWS have problems with learning, behavior, and have certain health problems. The biggest health problems have to do with overeating and weight gain.

Causes of PWS

PWS is caused by a genetic problem on chromosome 15q11-q13.


Diagnosis is made by a blood test. This genetic testing is usually suggested when symptoms or seen. For example, when an infant has low muscle tone and poor feeding, or when an older child with low muscle tone has overeating and too much weight gain.

How Many People Have PWS?

PWS is very rare. It affects approximately 1 out of every 12,000 to 15,000 children. Rates are similar in boys and girls.

Associated Developmental and Learning Issues

  • Movement/mobility difficulties: Most children with PWS have trouble with coordination and strength.
  • Communication difficulties: Many children with PWS develop speech skills later than other children their age.
  • Learning: Children with PWS have a range of intellectual abilities. Most children have mild intellectual problems.

Associated Medical Conditions

Many children with PWS have other health complications. It's important that these are recognized and treated. A child with PWS who is physically healthy is more likely to do well in school and in other treatments. This contributes to more independence, better daily functioning, and better quality of life. 

Because of this, it is important for a child’s primary care provider to know about PWS and how to look for common problems. Guidance for primary care providers is available through the American Academy of Pediatrics’ Health Supervision for Children with Prader-Willi Syndrome report.

Common Health Issues

  • Bone and muscle problems such as scoliosis and osteoporosis
  • Breathing problems
  • Dental problems
  • Endocrine problems (low levels of certain hormones such as growth hormone and thyroid hormones)
  • Gastrointestinal problems
  • Hypotonia (low muscle tone)
  • Overeating and obesity: During the preschool years, many children begin to grow too well. Children seem to be always hungry, called hyperphagia. Hyperphagia is a problem that continues through adulthood. Children and adults with PWS usually need less calories (typically 1,000-1,200 kcal per day for adults), because of low muscle strength and low physical activity. A balanced, low-calorie diet with vitamin and calcium supplementation is suggested.
  • Seizures and other neurologic issues
  • Sleep problems, including sleep apnea
  • Slow growth and feeding problems in infancy: Many infants with PWS have a low birth weight and trouble feeding.  Feeding may be slow due to the poor muscle tone and coordination. Some babies have trouble with choking and swallowing. Some babies need feeding tubes to help with getting enough nutrition.
  • Undescended testicles, small penis, small clitoris
  • Unusual reaction to anesthesia and other medicines

PWS itself does not get worse over time. However, how it affects a person may be different at different points in the person’s life.  Behavioral symptoms can bet better, worse, or stay the same during the course of a person’s life. Although PWS is not "curable" in the usual sense, treatment can help improve function and prevent complications.

Associated Behavioral Conditions

  • ADHD
  • Anxiety
  • Depression
  • Food-seeking behaviors
  • Rigidity, compulsions, Obsessive-Compulsive Disorder
  • Skin-picking
  • Tantrums

Related Services

URMC Collaborations


You can find resources for PWS in our Resource Directory!