Prader-Willi syndrome


Prader-Willi syndrome


Prader-Willi syndrome (PWS) is a rare genetic condition that causes a wide range of problems.

These may include:

a constant desire to eat food, which seems driven by a permanent feeling of hunger and can easily lead to dangerous weight gain

restricted growth, leading to short stature

reduced muscle tone (hypotonia)

learning difficulties

lack of sexual development

behavioural problems, such as temper tantrums or stubbornness

What causes Prader-Willi syndrome?

Prader-Willi syndrome is caused by a genetic defect on chromosome number 15, which happens purely by chance.

The condition is rare, affecting no more than one in every 15,000 children born in England. Boys and girls of all ethnic backgrounds may be affected.

Diagnosing Prader-Willi syndrome

Prader-Willi syndrome can usually be confirmed by carrying out genetic tests.

A checklist of symptoms that are typical of Prader-Willi syndrome is often used to identify children who should be tested.

Living with Prader-Willi syndrome

There's no cure for Prader-Willi syndrome, so treatment aims to manage the symptoms and associated problems. For parents, this includes dealing with their child's excessive eating and behavioural problems.

Trying to get your child to stick to a healthy, balanced diet and maintain a normal weight is one of the most important parts of caring for a child with Prader-Willi syndrome. It's also probably one of the most challenging and frustrating.

If children are allowed to eat as much as they want, they'll quickly become dangerously overweight. A child with the syndrome can eat three to six times more than other children of the same age and still feel hungry.

However restricting a child's diet is not easy. They can be highly obsessive when it comes to eating, and their hunger can cause them to hide or steal food.


While Prader-Willi syndrome itself isn't life- threatening, the compulsive eating and resulting weight gain can be.

Young adults with the syndrome often develop obesity-related conditions usually seen in older adults, such as type 2 diabetesand heart failure. If the obesity isn't treated, a person with the syndrome will probably die a lot younger than would normally be expected.

Compulsive eating can also cause health problems such as an abnormally expanded stomach and choking. Due to the potential risk of choking, all parents of a child with Prader-Willi syndrome are advised to learn the Heimlich manoeuvre. 

If a child with Prader-Willi syndrome is able to follow a restricted diet and control their weight, there's no reason why they can't enjoy a good quality of life and take part in activities such as voluntary or part-time work. However, because of their behavioural problems and learning difficulties, it's unlikely they'll be able to live fully independent lives.


The Prader-Willi Syndrome Association UK (PWSA UK) provides information and support for people whose lives are affected by PWS. You can call the PWSA helpline on 01332 365676.

Problems associated with Prader-Willi syndrome  

Prader-Willi syndrome (PWS) can cause a wide range of problems that will affect your child's physical, psychological and behavioural development.


Floppiness due to weak muscles is a characterisitc of Prader-Willi syndromethat usually becomes apparent shortly after birth. The medical name for this is hypotonia.

Hypotonia can mean your baby:

doesn't have a full range of movement

has a weak cry

has poor reflexes

can't suck properly, which means they may have feeding difficulties and be underweight until the age of one, and they may need to be fed with a feeding tube or artificial nipple (see managing Prader-Willi syndrome)

Poor sexual development

Poor sexual development (hypogonadism) is another feature that becomes apparent after birth. Hypogonadism is underactivity of the testicles or ovaries, and the effects that this causes.

Baby boys may have an abnormally small penis and one or both testicles may still be inside their abdomen (undescended testicles). Baby girls will also have under-developed genitalia.

Children will experience puberty later than usual and may not go through full development into an adult. In boys, the voice may stay high-pitched and they may not have much facial and body hair. Girls will have delayed periods that often don't start until their 30s, and a lack of normal breast development. When periods do occur, they're usually irregular and very light.

It's almost unknown for either men or women with Prader-Willi syndrome to have children because they are usually infertile due to a lack of development of testicles and ovaries. However, sexual activity is usually possible, particularly if sex hormones are replaced.

Distinctive facial features

Children with Prader-Willi syndrome have several distinctive facial features usually noticeable at, or shortly after, birth. These are:

almond-shaped eyes

narrowing of the forehead at the temple

narrow bridge of the nose

thin upper lip and a downturned mouth

Overeating and obesity

Children with Prader-Willi syndrome eat an excessive amount of food, much more than the body needs to meet its energy requirements. The medical name for this is hyperphagia.

A child will start to overeat between the ages of one and four. By the time they reach school age, they may start to hide or steal food, steal money to buy food and even eat inappropriate things, such as food waste or frozen food.

Children with Prader-Willi syndrome can tolerate much larger amounts of food before their body automatically vomits it back up, and they're not as sensitive to pain. Therefore, they can eat objects that would make other people very ill. This means they're at higher risk of food poisoning and choking.

If the child's overeating isn't managed, they'll become obese which could lead to further, serious, long-term health conditions later in life, such as type 2 diabetes.

Children with Prader-Willi syndrome also have a slow metabolism, which means it takes them longer to burn off energy from food. Lack of muscle tone contributes to them being less physically active than other children, which also increases their risk of becoming obese.

Stomach rupture

When a person eats too much in a short space of time, the stomach can split open. This is known as gastric rupture. It can cause bacteria to be released into otherwise germ-free parts of the body, which can trigger a life-threatening infection.

People with Prader-Willi syndrome who have a healthy or relatively healthy weight seem to be more at risk of gastric rupture than very obese people. This could be because their stomach shrinks after they've successfully controlled their eating habits for many months. If they then suddenly eat a large quantity of food, their shrunken stomach is unable to cope with it.

Vomiting and stomach pain are the two most common signs of a gastric rupture. People with Prader-Willi syndrome don't usually vomit or complain about stomach pain, so take these symptoms very seriously if they happen to your child. Call your care team or GP immediately for advice.

Learning difficulties

Most children with Prader-Willi syndrome have mild to moderate learning difficulties with a low IQ. This is usually in the range of 50-85, which is moderate to borderline intellectual disability.

This means it will take longer for a child with Prader-Willi syndrome to reach important developmental milestones. For example, a child with the syndrome will typically begin sitting up at around 12 months and start walking and talking at around 24 months.

Most children with Prader-Willi syndrome can attend a mainstream school, although they may find some activities challenging, such as understanding and responding to verbal instructions and dealing with subjects such as maths. Their short-term memory is usually poor, although they often have a good long-term memory.

Despite these problems, children with Prader-Willi syndrome tend to be good at solving puzzles, such as word search puzzles and jigsaws.

Short stature

Children with Prader-Willi syndrome are usually much shorter than other children of their own age. This is usually apparent by the time they're two years old, and becomes particularly noticeable when they reach their 20s.

Low levels of human growth hormone (HGH) contribute to the short stature, and they won't go through the typical growth spurt during puberty.

If HGH isn't replaced, the average adult height for a man with Prader-Willi syndrome is 159cm (5 feet 2 inches) and 149cm (4 feet 10 inches) for a woman.

Children can be prescribed an artificial version of HGH to encourage growth (see managing Prader-Willi syndrome).

Behavioural problems

Most children with Prader-Willi syndrome will develop temper tantrums and fly into sudden rages. Tantrums may be triggered by certain things, such as if the child is denied food or doesn't get their own way.

Other typical behavioural problems include:

stubbornness and being very argumentative

controlling and manipulative behaviour

asking the same question over and over again, or frequently returning to the same topic in a conversation

persistent lying and refusing to accept blame

Many children will engage in compulsive behaviour, such as collecting objects or having a very strict daily routine, and any unexpected disruption to the routine can upset them.

The behavioural problems tend to get worse as the child gets older, before improving as they develop into an adult.

While these behavioural problems can be challenging for parents to deal with, children with Prader-Willi syndrome also have many positive aspects to their personality, such as being affectionate, kind, caring and funny.

Skin picking

As many as four out of five children with Prader-Willi syndrome persistently pick their skin, usually their face, hands or arms. They may scratch, pierce or pull at their skin, sometimes using paper clips or tweezers. It can result in open sores, scarring and infection.

Some children may pick out pieces of faeces from their bottom. As well as causing embarrassment for children and parents, it can result in rectal bleeding and infection.

Sleep problems

Many children with Prader-Willi syndrome have problems sleeping. For example, they may have interrupted breathing during sleep. This is known as sleep apnoea, and it occurs when the upper airway becomes blocked causing snoring and brief episodes where breathing actually stops followed by arousal.

These episodes of interrupted sleep cause excessive sleepiness in the day which contributes to inactivty and obesity. The problem itself is made worse by weight gain, leading to a vicious cycle. In addition, the lack of oxygen in the night is dangerous in its own right.

It's important to identify sleep apnoea because very effective treatment and support is available. 

Other features

Other features of Prader-Willi syndrome can include:

unusually fair hair, skin and eyes

small hands and feet

narrow hands

crossed eyes



decreased production of saliva, which can cause tooth decay

skin that's easily bruised

difficulty pronouncing certain sounds and words properly

abnormal curvature of the spine (scoliosis)

Weakening of the bones (osteoporosis) is common in adults with Prader-Willi syndrome because they don't have the sex hormones needed to keep bones healthy.

High pain and vomiting tolerance

Children with PWS have a high tolerance to pain, which can be potentially dangerous.

For example, a serious condition such as appendicitis would cause severe pain in most people, but may pass unnoticed or be a minor upset for a child with PWS.

Therefore, if a child with PWS does complain of pain, it should be taken seriously.

Causes of Prader-Willi syndrome 

Prader-Willi syndrome (PWS) is caused by a genetic defect onchromosome number 15.

Genes contain the instructions for making a human being. They're made up of DNA and packaged onto strands called chromosomes. A person has two copies of all their genes, which means chromosomes come in pairs.

Humans have 46 chromosomes (23 pairs). One of the chromosomes that belongs to pair number 15 is abnormal in Prader-Willi syndrome.

Around 70% of cases of Prader-Willi syndrome are the result of missing genetic information from the copy of chromosome 15 inherited from the father. This defect is referred to as "paternal deletion".

Paternal deletion is thought to occur entirely by chance, so it's practically unheard of to have more than one child with Prader-Willi syndrome caused by paternal deletion.

However, if Prader-Willi syndrome is caused by a different type of problem with chromosome 15, there's a very small chance you could have another child with the syndrome.

Effect the chromosome defect has on the brain

It's thought the defect in chromosome 15 disrupts the normal development and functioning of part of the brain called the hypothalamus.

The hypothalamus plays a role in many of the body's functions, such as producing hormones and helping regulate appetite. A malfunctioning hypothalamus may explain some of the typical features of Prader-Willi syndrome, such as delayed growth and persistent hunger.

Studies using advanced brain imaging technology have shown that after eating, people with Prader-Willi syndrome have very high levels of electrical activity in a part of the brain known as the frontal cortex. This part of the brain is associated with physical pleasure and feelings of contentment. It may be possible that people with Prader-Willi syndrome find the act of eating immensely rewarding, much like a drug-induced high, and are constantly seeking food to achieve that high.

Another theory is that in Prader-Willi syndrome the hypothalamus can't judge the level of food in the body as it usually does. This means that a person with the syndrome always feels hungry no matter how much food they eat.

Diagnosing Prader-Willi syndrome 

A definitive diagnosis of Prader-Willi syndrome (PWS) can usually be made by running a series of genetic tests.

Genetic testing

Genetic testing can be used to check the chromosomes in a sample of your child's blood for the genetic abnormalities known to cause Prader-Willi syndrome.

As well as confirming the diagnosis of Prader-Willi syndrome, the results should also allow you to determine the likelihood of having another child with the syndrome.

Checklist for diagnosing Prader-Willi syndrome

A checklist of symptoms known to be typical of Prader-Willi syndrome is also used to identify which children should be tested.

The checklist can also be helpful for parents concerned about their child's development, behaviour and eating habits, and who want to know whether their child may have Prader-Willi syndrome.

Major criteria

One point is given for each of the following symptoms a child has:

floppiness and weak muscles that becomes apparent during or shortly after birth

feeding problems and failure to grow during the first year of life

rapid weight gain in children aged one to six years

characteristic facial features, such as almond-shaped eyes and thin upper lips

underactive testicles or ovaries (hypogonadism), resulting in delayed sexual development

delayed physical development or learning difficulties

Minor criteria 

Half a point is given for each of the following symptoms a child has:

lack of movement during pregnancy, such as kicking in the womb, or the baby has an unusual lack of energy after birth

sleep disturbances, such as sleep apnoea

delayed or absent puberty

unusually fair hair, skin and eyes

narrow hands

thick and sticky saliva

crossed eyes or long-sightedness (hyperopia)

problems pronouncing words and sounds properly

frequent skin picking

Overall score

If your child is under the age of three and scores five points, with at least three points from the major criteria, Prader-Willi syndrome would be strongly suspected and genetic testing would be recommended.

If your child is over the age of three and scores eight points, with at least four points from the major criteria, Prader-Willi syndrome would be strongly suspected and testing would be recommended.

Managing Prader-Willi syndrome: a guide for parents 

There's no cure for Prader-Willi syndrome (PWS), but a team of different healthcare professionals will help you manage any problems your child has due to the syndrome, such as overeating, and treat any associated conditions.

A care plan will be drawn up to address your child's problems and needs. The plan will be continually reassessed as your child gets older and their needs change.

You and your child will also be given a key worker who will be your point of contact for the various support services available. While your child is young, it's likely the key worker will be a health visitor. As your child gets older and their needs become more complex, it's likely the key worker will be a social worker.

Most adults with Prader-Willi syndrome are unable to live fully independent lives, such as having a full-time job and living in their own home. Their behavioural issues and problems with food mean these environments and situations are too demanding. Adults with the syndrome who don't live with their parents will probably requireresidential care.

Below is a guide to managing the various problems and symptoms commonly seen in babies, children and teenagers with Prader-Willi syndrome.