What Is Prader-Willi Syndrome?

What Is Prader-Willi Syndrome?

Prader-Willi syndrome is a rare and complex genetic disorder that results in a number of physical, mental, and behavioral issues. Prader-Willi syndrome is the leading cause of life-threatening childhood obesity, due to the constant hunger that children with Prader-Willi syndrome develop, usually around the age of two. The Special Olympics Arizona team is breaking down Prader-Willi syndrome: what it is, the signs, symptoms, causes, and what to expect if your child has Prader-Willi syndrome.

What Is Prader-Willi Syndrome?

Prader-Willi syndrome, commonly referred to as PWS, is a rare genetic disorder that affects a child’s metabolism and causes changes to their body and behavior. Children with PWS generally have severely low muscle tone and experience poor feeding during infancy, followed by an insatiable appetite that usually develops in children between the ages of 2 and 6 years old. If excessive eating isn’t managed in children with PWS, they may become life-threateningly obese. PWS is also characterized by a delay in early childhood milestones and puberty. There can also be rare, life-threatening complications associated with PWS, such as respiratory illnesses, obesity-related cardiovascular problems, diabetes, and sleep apnea.

What Are the Signs & Symptoms of Prader-Willi Syndrome?

Prader-Willi syndrome affects each child differently, and different signs and symptoms may occur at different ages.


In infants, signs and symptoms that may appear in those with PWS include:

  • A weak cry
  • Lethargy, or tiredness
  • Poor feeding ability
  • Weak muscle tone

Some physical symptoms may be evident in infancy but could develop or increase in noticeability over time. These symptoms include:

  • Almond shaped eyes
  • A long, narrow head
  • A triangular mouth
  • Short height
  • Small hands and feet
  • Underdeveloped genitals

Early Childhood to Adulthood

Behavioral symptoms may begin to develop in your child as they age. In addition to the insatiable appetite, which can develop anywhere from age 2 to age 6, they may also have:

  • Temper tantrums, emotional outbursts or extreme stubbornness
  • Problems with cognitive development or an intellectual disability
  • Obsessive or compulsive behaviors, such as skin picking
  • Sleep apnea or other sleep abnormalities
  • Eating challenges, like not feeling satisfied after consuming a meal or eating very large amounts

A pediatrician or other healthcare provider may diagnose Prader-Willi syndrome after a physical examination and a series of tests. A physician will generally look for physical symptoms similar to those outlined below and ask you a series of questions about your child’s symptoms, including their eating habits, which are relevant in cases of Prader-Willi syndrome. If your provider suspects PWS, they will run genetic testing, which will confirm if there are abnormalities in your child’s DNA.

Prader-Willi Syndrome Causes

Genes on chromosome 15 that lose function are the genetic cause of Prader-Willi syndrome. At conception, you inherit one copy of chromosome 15 from each parent; the parental chromosome turns on and the maternal chromosome is turned off, but both are necessary for genes to get the instructions needed for your body to develop and function. This is called genomic imprinting, and there are a variety of ways in which chromosome 15 can lose function, resulting in Prader-Willi syndrome.

Chromosomal Deletion

Most cases of Prader-Willi syndrome, nearly 70%, result from chromosomal deletions. This is when part of the paternal chromosome 15 is missing in each cell. Symptoms arise because the paternal chromosome 15, which is meant to be turned on to provide instructions to the body, is either missing or not working properly, while the maternal chromosome 15 is present but turned off.

Maternal Uniparental Disomy

About 25% of cases of Prader-Willi syndrome occur when a child inherits two chromosome 15s from the maternal genes instead of inheriting one from each biological parent. This will result in both chromosome 15s being turned off since they are the maternal gene.


Less than 1% of PWS cases occur due to translocation, when a chromosome relocates itself to another chromosome. This makes the genes that chromosome 15 is producing work ineffectively, since they are not located where they should be.

Prader-Willi Syndrome Treatment

Treatments for Prader-Willi syndrome involve managing challenges and preventing complications. Treatment options include:

  • Devices such as special bottle nipples to help an infant receive proper nutrients
  • Helping your child eat properly, with a low calorie diet and limiting unnecessary overeating
  • Medications to increase amounts of certain hormones, including growth hormone, testosterone or human chorionic gonadotropin for boys and estrogen for girls
  • Supportive therapies such as physical therapy, speech-language therapy, and special education to improve physical and cognitive function

How Common Is Prader-Willi Syndrome?

Prader-Willi syndrome is rare, affecting around 1 in every 10,000 to 30,000 people in the world.

What to Expect if Your Child Has Prader-Willi Syndrome

Prader-Willi syndrome is a genetic disorder that is not preventable and has no cure, but the treatment options are plentiful for your child. As a parent, having ample information on your child’s condition can help you prepare yourself and your child for challenges they might face due to PWS. With early intervention and ongoing treatments, your child can have a normal lifespan. As they enter elementary school, it may be common that they need extra help and extra attention on certain subjects. It is common for individuals to need lifelong support to achieve as much independence as possible and to live a healthy life. Visiting a nutritionist can help you ensure your child has a meal plan and diet that helps them meet their nutritional needs without consuming too much. Mental health professionals may help you and your child cope with the difficulties of Prader-Willi syndrome and can help you and your child discover ways to adapt and ways that they can grow and meet their full potential. PWS is rare, but there is a community out there that can provide guidance and knowledge and give you and your child a group of parents and children to connect with.

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