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What is Prader-Willi syndrome?

Prader-Willi syndrome is a rare condition that causes problems of the body, emotional, and actions. It’s normal to have a constant feeling of hunger.

An individual with Prader-Willi Syndrome (PWS) has severe trouble regulating their body weight, as they spend a long time eating and have a strong urge to consume as much food as possible. PWS is the most frequent genetic cause of childhood morbid obesity.

According to the United States Prader-Willi Syndrome Association about 1 in 8,000 and 1 in 25,000 individuals are diagnosed with the condition.

Some studies say that the condition exists globally between 1 in 10,000, and 1 in 30,000. It affects males and females equally.

What is PWS?

Genetics images
PWS occurs when genes are missing on chromosome 15.

PWS is a genetic disorder which means it is inherited by people from their parents.

It is present from birth but there is often no diagnosis until later in life.

Individuals with PWS have seven genes which are either deleted or inactive on chromosome 15.

They will also have poor muscle tone, sexual growth incomplete, and chronic hunger.

By contrast with people who do not have the disorder, their metabolism appears to eat less calories. A lot of people with PWS are of short stature.

A newborn baby with PWS appears to have a lower birth weight than average, poor muscles and sucking difficulties. Weakness in the muscle is known as hypotonia.

Individuals begin to grow a heavy appetite, called hyperphagia, between the ages of 2 and 5 and often older.

This characteristic occurs after eating due to a drastically decreased sensation of fullness. When hyperphagia starts it appears to be a disorder that lasts a lifetime.


Usually, PWS symptoms develop in 2 stages.

Sometimes, the first signs manifest within the first year of life, and some tend to develop between the ages of 1 and 6 years.

Symptoms in the first year

An infant is likely to have any or more of the following signs between 0 and 12 months of age:

  • Hypotonia, or poor muscle tone: The child feels floppy when another person is holding them. The elbows and knees may be loosely extended instead of firmly in position. Hypotonia improves with age.
  • Specific facial features: These may include almond-shaped eyes and a head that narrows at the temples. The mouth might have a small, turned-down appearance with a thin upper lip.
  • Reduced physical development: Poor muscle tone can reduce sucking ability, making feeding difficult. The infant may gain weight at a slower rate than other babies.
  • Strabismus: The eyes do not move in unison. One eye may appear to wander, or the eyes may cross.

Often, the baby may have an exceptionally weak cry, show incomplete stimulus responses and appear exhausted.

Genitals can not grow properly, and often there is depigmentation of the skin and eyes.

Symptoms from age 1 to 6 years

Between 1 and 6 years of age, the following symptoms may occur:

  • Food cravings and gain in body weight: The child craves food constantly, eating large amounts of food with great frequency. They may hoard food or eat items that most people would not, such as frozen food before it is thawed or cooked or food that has passed its expiry date.
  • Hypogonadism: The testes or ovaries do not produce enough sex hormones, resulting in underdeveloped sex organs. The testes of males with PWS may not descend.
  • Limited growth and strength: This can include poor muscle mass, as well as small hands and feet. People with PWS may not reach full height, as an adult, due to a shortage of growth hormone.
  • Limited cognitive development: This might lead to mild to moderate learning disabilities.
  • Delayed motor skills: Children might reach the common milestones of progress in learning coordination skills, such as sitting up or walking, later than usual. The infant may not walk until 24 months old.
  • Delayed verbal skills: A child with PWS may develop their speech capabilities later than is typical.
  • Behavior and mental disorders: These may include temper tantrums, especially relating to food. The child may be argumentative, oppositional, rigid, manipulative, possessive, and stubborn. Some children may have obsessive-compulsive disorder (OCD), repetitive behaviors, recurring thoughts, and other mental disorders. Excessive skin-picking and nail-biting may occur.
  • Sleep disorders: These may include sleep apnea, possibly due to obesity. There may be disturbances of the normal sleep cycle.
  • Scoliosis or curvature of the spine: This is a symptom that can occur as the individual with PWS grows.
  • Depigmentation: The skin and hair may be fairer than that of parents and siblings.

Pain can be extremely sensitive. Short-sightedness is normal too.

The Prader-Willi Syndrome Association is now gradually treating PWS as a multi-stage condition instead of just the two that were originally used.

Around 18 to 36 months in Phase 2, body weight moves from being below normal to higher without any extra value in food or calorific consumption.

Phase 3 begins at around 8 years of age, and will continue to adulthood. Relentless quest for food starts, and is a key feature of this level.

Children with PWS are going on experiencing impaired sexual growth during puberty.

When to see a doctor

Doctor checking a child temperature
Parents should consult a doctor if the baby has difficulty feeding.

Parents should consult a doctor if the following signs appear:

  • difficulty feeding at the infant stage
  • problems waking up
  • a lack of response to normal stimulation
  • floppiness when held
  • the constant seeking of food in a child
  • rapid weight gain

Certain warning signs include excessive hunger, continuing food quest and, generally, rapid weight gain. Nonetheless, there will almost always be other symptoms, and the majority of children who display such behaviors will not have PWS.


Anomalies in genes cause PWS. Scientists found the abnormality on chromosome 15 but the genes involved have not yet been identified.

In addition to those relating to sex, all human genes come in pairs. Another copy comes from the father and is called the paternal gene, and the other copy comes from the mother and is known as the mother gene.

For PWS certain paternal genes on chromosome 15 are either incomplete or not functioning properly.

This genetic mutation changes the functions of the hypothalamus. The hypothalamus is a part of the brain which controls hunger and thirst. It also releases hormones that facilitate the sexual growth and development.

If, for example, a head injury, tumor, or tumor-removal surgery damages the hypothalamus, signs and symptoms similar to PWS that develop.

Despite not having the genetic characteristics of PWS, the person with a damaged hypothalamus may experience some of the same behavioral issues, such as frequent cravings of food.

The medication used by people born with PWS can also assist those with symptoms acquired similar to those common to the disease.


A variety of tests are available for PWS, but a form of genetic testing called DNA methylation can detect 99 percent of cases.

Early testing is important, as early diagnosis makes prompt treatment possible.

Some people with PWS do not get a diagnosis or a misdiagnosis of Down’s syndrome or autism spectrum disorder ( ASD) is given, as some features of these conditions overlap with PWS’s.


A nutritional therapist may prescribe high-calorie milk formula for an infant with feeding difficulties.
A nutritional therapist may prescribe high-calorie milk formula for an infant with feeding difficulties.

There is no cure for PWD.

However, ongoing treatments may help to alleviate symptoms by concentrating on related hormone disorders and developmental ones.

Therapies that doctors might use include:

  • nutrition
  • growth
  • sex hormones
  • physical
  • speech
  • occupational
  • developmental

Nutrition therapy may include high-calorie milk formula for an infant experiencing feeding difficulties.

A doctor who treats PWS will monitor weight and growth closely, while a nutritionist may help develop a nutrient dense, low-calorie diet that promotes weight control.

People with PWS have to adopt a very strict diet with lower-calorie targets than the age group should have normal. Parents and guardians may have to put in place physical barriers to compensate for food cravings, such as locking food within kitchen cabinets.

Growth hormone therapy may help promote development and the body fat, although it is uncertain the long-term effects of these.

Treatment of sex hormones, such as hormone replacement therapy ( HRT), will build up testosterone for boys and girls of progesterone. It helps with sexual health, and can reduce osteoporosis risk.

Other treatments include:

  • developmental therapy to encourage age-appropriate social and interpersonal skills
  • occupational therapy to help with routine tasks
  • physical therapy to manage coordination and movement
  • speech therapy to promote communication ability

A person with PWS may also need to consult a psychologist or psychiatrist on the psychological effects of PWS for assistance.

Many people with PWS require constant monitoring and advanced care. Continuous control of food and behavior modification may bring stress to family members and family support and therapy services may also offer relief.


PWS complications may involve having unexpected reactions to medications, including sedatives and anesthesia.

An individual with PWS may have a usually high pain threshold, meaning no medical attention would be given to an infection or illness until its later stages. Vomiting in people with PWS is also uncommon, unless a condition is already serious.

The high prevalence of obesity implies a higher risk of type 2 diabetes, heart disease and stroke compared to others. Similarly, people with PWS experience higher tooth erosion rates than others. Osteoarthritis and osteoporosis can also occur and affect the bones and joints.


PWS is a disorder in which an individual can not suppress the desire to eat due, among other symptoms, to a chromosomal anomaly, impaired growth and poor cognitive development.

The symptoms develop in stages, and early identification can help a person manage the condition.

When a person with PWS is able to manage both obesity and the other complications of the disease, little, if any, changes in life expectancy can be expected.

Individual medical care is critical throughout life, however, and particularly once a person with PWS reaches the age of 40.

Chukwuebuka Martins

Chukwuebuka Martins is a writer, researcher, and health enthusiast who specializes in human physiology. He takes great pleasure in penning informative articles on many aspects of physical wellness, which he then thoroughly enjoys sharing to the general public.