Prader-Willi Syndrome: Symptoms, warning signs, and causes

Prader-Willi syndrome is a rare condition that causes physical, mental, and behavioral problems. An unrelenting feeling of hunger is common.

A person with Prader-Willi Syndrome (PWS) has extreme difficulty controlling their body weight, as they spend a long time eating and have a powerful compulsion to eat as much food as possible. PWS is the most common genetic cause of morbid obesity in children.

According to the Prader-Willi Syndrome Association in the United States, between 1 in 8,000 and 1 in 25,000 people live with the condition.

Other sources suggest the syndrome occurs in between 1 in 10,000 and 1 in 30,000 people globally. It affects both sexes equally.

What is PWS?

PWS occurs when genes are missing on chromosome 15.

PWS is a genetic condition, which means that people inherit it from their parents.

It is present from birth, although a diagnosis often does not occur until later in life.

People with PWS have seven genes on chromosome 15 that are either deleted or inactive.

They will often have low muscle tone, incomplete sexual development, and chronic hunger.

Their metabolism tends to burn fewer calories when compared to people who do not have the condition. Many individuals with PWS have short stature.

A new-born infant with PWS tends to have a lower-than-usual birth weight, weak muscles, and difficulties with sucking. Muscle weakness is known as hypotonia.

Individuals start developing a strong appetite called hyperphagia between 2 and 5 years of age and sometimes later.

This characteristic occurs due to a significantly decreased feeling of fullness after eating. Once hyperphagia begins, it tends to be a lifelong condition.


Symptoms of PWS typically develop in two stages.

The first symptoms often emerge during the first year of life, and others start to occur between the ages of 1 and 6 years old.

Symptoms in the first year

Between 0 and 12 months of age, an infant is likely to have some or all of the following symptoms:

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.

The infant may also have an unusually weak cry, display incomplete responses to stimulation, and appear tired.

Genitals may not develop correctly, and depigmentation of the skin and eyes sometimes occurs.

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.

There may be a high tolerance for pain. Short-sightedness is also common.

The Prader-Willi Syndrome Association is now increasingly seeing PWS as a syndrome of multiple stages rather than just the two used initially.

In Phase 2, at 18 to 36 months, body weight crosses over from being lower than average to higher without any additional interest in food or calorific intake.

Phase 3 starts around the age of 8 years and can carry on to adulthood. Relentless food-seeking begins and is a key feature of this stage.

Going forward, people with PWS undergo poor sexual development during puberty. Females may experience scant menstruation or none at all, and most adults with PWS may not be able to reproduce.

prader-willi syndrome doctor
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

Other warning signs include constant hunger, continual searching for food, and, usually, rapid weight gain. There will almost always be other signs, though, and most children who exhibit these behaviors do not have PWS.

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