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Prader-Willi syndrome


Prader-Willi syndrome (PWS) is a rare genetic condition. It causes a wide range of symptoms, such as:

  • a constant desire to eat food, which seems to be driven by permanent hunger and can easily lead to dangerous weight gain
  • restricted growth
  • learning difficulties
  • behavioural problems, such as temper tantrums or stubbornness

See Prader-Willi syndrome - symptoms for more information

Who is affected?

PWS is rare, affecting between 1 in every 15,000 to 1 in every 20,000 children born in Wales. Boys and girls of all ethnic backgrounds may be affected.

There are no known factors that make giving birth to a child with PWS more likely. It is caused by a fault in the child's chromosomes, which happens purely by chance. See Prader-Willi syndrome - causes for more information.

Living with Prader-Willi syndrome

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

See Prader-Willi syndrome - management for more information.

Restricting your child's diet is a particularly important part of managing their condition. If children with PWS are allowed to eat as much as they want, they will quickly become dangerously overweight. They will eat three to six times more than other children of the same age, and will probably still feel hungry.

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


While PWS itself is not life threatening, the compulsive eating and the resulting weight gain can be.

Younger adults with PWS often develop obesity-related conditions usually seen in older adults, such as type 2 diabetes and heart failure. If the obesity is not treated, an adult with PWS 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. Because of the potential risk of choking, all parents of a child with PWS are advised to learn the Heimlich manoeuvre.

If a child with PWS manages to follow a restricted diet and control their weight, there is no reason why they cannot 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 is unlikely they will be able to live fully independent lives.

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Prader-Willi syndrome (PWS) can cause a wide range of symptoms that will affect your child’s physical, psychological and behavioural development. These symptoms are described below.


A feature of PWS that becomes apparent shortly after birth is your baby being unusually floppy due to weak muscles. The medical name for this is hypotonia.

Hypotonia can mean your baby:

  • does not have a full range of movement
  • has a weak cry
  • has poor reflexes
  • cannot suck properly, which means they may have feeding difficulties and be underweight until the age of one, and may need to be fed with a feeding tube or artificial nipple (see Prader-Willi syndrome - treatment for more information)

Poor sexual development

Another feature that becomes apparent after birth is hypogonadism. Hypogonadism means that the child has underactive testicles or ovaries, which play an important role in sexual development and reproduction.

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

In later life, the child will go through puberty later than usual and may not go through full development into an adult. In boys, the voice may stay high pitched like a child's and they may not have much facial and body hair. Girls will have delayed periods that often do not begin until their 30s. When periods do occur, they are usually irregular and very light.

Distinctive facial features

Children with PWS have several distinctive facial features that are 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 an upturned mouth

Overeating and obesity

Children with PWS 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 PWS can tolerate much larger amounts of food before their body automatically vomits it back up, and they are not as sensitive to pain (see below). Therefore, they can eat objects that would make other people very ill. This means they are at higher risk of food poisoning and choking.

Children with PWS have a high pain tolerance, 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.

If their overeating is not managed, they will soon become obese.

Children with PWS also have a slow metabolism, which means it takes them longer to burn off energy from food. They are also usually less physically active than children without the condition, 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 life-threatening infections.

It is thought that as many as 1 person in 35 with PWS dies as a result of this.

People with PWS 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 have successfully controlled their eating habits for many months. If they then suddenly eat a vast quantity of food, their shrunken stomach cannot cope with it.

The two most common signs of a gastric rupture are vomiting and stomach pain.

People with PWS do not usually vomit or complain of 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 PWS have mild to moderate learning difficulties and a lower-than-average IQ.

This means that it takes longer for a child with PWS to reach important developmental milestones. For example, a child with PWS will typically begin sitting up at around 12 months and start walking and talking at around 24 months.

Most children with PWS 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 mathematics. Their short-term memory is usually poor, although they often have a good long-term memory.

Despite these problems, children with PWS tend to be good at solving puzzles, such as wordsearch puzzles and jigsaws.

Short stature

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

They are short because they have low levels of human growth hormone (HGH) and they will not go through the typical growth spurt during puberty.

If this is not treated, the average adult height for a man with PWS is 159cm (5 feet 2 inches) and 149cm (4 feet 10 inches) for a woman.

Children can be prescribed an artificial version of human growth hormone to encourage growth (see Prader-Willi syndrome - treatment for more information).

Behavioural problems

Most children with PWS 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 does not get their own way.

Other typical behavioural problems are:

  • 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, and then improve as they develop into an adult.

While these behavioural problems can be challenging for parents to deal with, children with PWS 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 PWS 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 back passage. As well as causing embarrassment for children and parents, this can result in rectal bleeding and infection.

Sleep problems

Many children with PWS have problems with sleeping. For example, they may have interrupted breathing during sleep, known as sleep apnoea, which causes them to feel excessively sleepy the next day. This can be made worse by weight gain, so can be more of a problem when they get older.

Other features

Other features of PWS can include:

  • unusually fair hair, skin and eyes
  • small hands and feet
  • narrow hands
  • crossed eyes
  • short-sightedness
  • long-sightedness
  • decreased production of salvia, which can cause tooth decay
  • skin that gets easily bruised
  • difficulty pronouncing certain sounds and words properly
  • abnormal curvature of the spine (scoliosis)

Weakening of the bones, known as osteoporosis, is common in adults with PWS because they do not have the hormones needed to keep bones healthy

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

Around 70% of cases of PWS 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 is practically unheard of to have more than one child with PWS that is caused by paternal deletion.

However, if PWS is caused by a different type of problem with chromosome 15, there is a chance, usually very small, that another child will have the condition.

Genes and chromosomes

Genes contain the instructions for making a human being. They are made up of DNA and packaged onto strands called chromosomes.

We have two copies of all our genes, so our chromosomes are in pairs.

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

How the chromosome defect causes PWS

It is thought that 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 functions of the body, such as producing hormones and helping regulate appetite. A malfunctioning hypothalamus may explain some of the typical features of PWS, such as delayed growth and persistent hunger.

Recent studies, using advanced brain imaging technology, have shown that after eating, people with PWS 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 PWS 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 PWS, the hypothalamus cannot judge the level of food in the body as it normally does. So no matter how much food the person eats, they always feel hungry.

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In the past there was no reliable test for Prader-Willi syndrome (PWS). The condition was diagnosed using a checklist of symptoms that are known to be typical of PWS.

Now, there is a reliable genetic test for PWS, although the checklist is still thought to be very useful for identifying which children should be tested.

It is also useful for parents who are concerned about their child’s development, behaviour and eating habits, and who want to know whether their child may have PWS.

Checklist for diagnosing Prader-Willi syndrome

Major criteria

Score one point for each symptom that your child has:

  • weak muscles and floppiness 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 old
  • characteristic facial features, such as almond-shaped eyes and thin upper lips
  • underactive testicles or ovaries (hypogonadism), which results in delayed sexual development
  • delayed physical development or learning difficulties

Minor criteria 

Score half a point for each symptom that your child has:

  • lack of movement during pregnancy, such as kicking in the womb, or the baby appears unusually lacking in 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
  • problems pronouncing words and sounds properly
  • frequent skin picking

Total score

If your child is under the age of three and scores five points, with at least three points from the major criteria, a diagnosis of PWS 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, a diagnosis of PWS would be strongly suspected and testing would be recommended.

Genetic testing

It is now possible to check chromosomes in a sample of your child’s blood for the genetic abnormalities known to cause PWS.

This test will not only confirm the diagnosis of PWS, but should also be able to determine exactly what type of chromosome defect is responsible for your child’s condition. This information should allow you to determine the likelihood of having another child with PWS (see Prader-Willi syndrome - causes).

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

A care plan will be drawn up to address your child's needs and any problems they have. The plan will be continually reassessed as your child gets older and their needs and situation change. See the next section, for a typical example of a care/treatment plan.

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, the key worker is likely to be a health visitor. As your child gets older and their needs become more complex, the key worker is likely to be a social worker.

Most adults with PWS cannot 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 that these environments and situations are too demanding. Adults with PWS who live away from their parents will probably require residential care.

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

A typical treatment plan

Treating problems in babies

Poor feeding

Problems with sucking mean that babies with PWS have difficulty feeding and do not gain as much weight as they should do in their first year of life.

Your baby will probably need to be fed through a tube placed in their nose and down their throat into their stomach.

After a few months, it is usually possible to feed your child normally using breast or bottle milk. You can use several techniques to encourage your baby to feed:

  • Hold your baby on your lap so both your hands are free. Use one hand to hold the nipple or bottle teat and the other hand to help close the baby’s lips.
  • Before introducing the teat or nipple into the baby’s mouth, stimulate their mouth by gently tapping or stroking their tongue, lips and cheeks.
  • If you are breastfeeding, you could place a bottle teat over your nipple. This allows you to help your baby suck by placing pressure on the teat.
  • You can help your baby’s suck reflex by placing your finger on their cheeks and gently stroking towards their lips. Once your baby begins to suck gently, pull back the nipple or teat to encourage them to hold on.
  • If your baby is having difficulties swallowing, stroke under their chin down to the top of their breastbone in a downward movement.

Several bottles are available that can make feeding easier. They are designed for children with a cleft lip or palate, a birth defect that affects the mouth, but are also useful for babies with PWS.

Undescended testicles

If you have a baby boy with undescended testicles, surgery is usually recommended to correct this in the first or second year of life.

Treatment is recommended for two reasons:

  • Your son will have an increased risk of developing testicular cancer if the testicle is not corrected.
  • Your son may have problems with his self-esteem and body image if he is "missing" one or both testicles

For more information, see Undescended testicles - treatment.

Managing weight and diet

Trying to get your child to stick to a healthy diet and maintain a normal weight is one of the most important parts of caring for a child with PWS. It is also probably one of the most challenging and frustrating.

If your child wants to eat frequent servings of food, most of those servings should be low in calories.

A recommended daily diet plan usually looks like this:

  • six to eight servings of vegetables a day – one serving is around half a cup of raw vegetables or one cup of cooked vegetables
  • three to five servings of bread, cereal, rice or pasta a day – one serving is one slice of bread, half a cup or 28g (1oz) of rice or pasta 
  • four servings of fruit a day – one serving is around half a cup of canned or fresh fruit, quarter of a cup of dried fruit or half a cup of fruit juice
  • two servings of milk, cheese or yogurt a day – one serving is around one cup of milk, 30g (1oz) of cheese or half a cup of sugar-free and fat-free yogurt 
  • one to two servings of meat, poultry, fish, eggs or dried beans a day – one serving is 60g (2oz) of cooked lean meat, fish or poultry, one egg, or half a cup of cooked dried beans

Restrict your child's access to sweets and fatty foods as much as possible.

Your care team can give you a more detailed diet plan that is individually tailored for your child.

Getting your child to stick to the plan voluntarily is practically impossible, so you will probably need to restrict your child’s access to food, for example by:

  • locking any storage devices that contain food, such as your fridge or cupboards (children with PWS have been known to eat food out of the bin or freezer, so you may need to restrict access to these too)
  • regularly searching your child’s room for hidden food
  • not allowing your child to leave the house unsupervised
  • not leaving your child unsupervised with other children who are eating, in case they try to steal other children’s food

It is also important to let relatives, friends, other parents and teachers know about the need to restrict your child’s diet.

Some medications have been used to try to suppress children’s appetites, but they have all been unsuccessful.

Weight-loss surgery is not recommended for children with PWS as they do not have the willpower to stick to the strict diet that is required after surgery.


Exercise is an important part of helping your child maintain a healthy weight. Children should do at least 60 minutes of exercise a day.

Many children with PWS have reduced energy levels. Therefore, it may be a good idea to break down their exercise into 5- to 10-minute sessions throughout the day to stop them getting tired and discouraged. Your child's care team should be able to recommend a suitable exercise plan.

Children with PWS usually prefer individual activities to team sports, such as:

  • swimming
  • walking
  • exercising in a gym

It is important not to promise food as a reward to encourage your child to participate in exercise, as this can encourage unhealthy behaviour.

Treating with growth hormones

Treatment with an artificial version of the human growth hormone (HGH) is usually recommended for most children with PWS.

The routine use of this treatment for children with PWS on the NHS only began in 2010, so it is difficult to know what effect treatment will have on adult height. Initial research suggests that HGH may help increase final adult growth by around 10.5cm (4.1 inches).

HGH also has other important health benefits:

  • It increases muscle size while lowering the amount of body fat.
  • It should increase energy levels, which will help your child become more physically active.
  • It helps normalise facial appearance, so the distinctive facial features associated with PWS become less noticeable.

It is usually recommended that a course of HGH begins in early childhood, around the ages of two to four years, and lasts for up to four years.

A type of HGH called somatropin is used to treat children with PWS. Somatropin is given by daily injection using an auto-injector syringe.

Most children tolerate somatropin well and side effects are uncommon.

Managing behavioural problems in children

Structure and routine

Most children with PWS cope best with a very structured environment and daily routine. For example:

  • Establish a regular daily routine and give plenty of advanced notice if any changes are planned.
  • Do not put pressure on a child to speed up to complete a task. Give them plenty of warning if they need to complete an activity, such as getting dressed to go out.
  • Ensure that other people, such as relatives and teachers, are briefed about how to interact with your child.
  • You may want to avoid eating in front of your child so they do not begin thinking about eating themselves.

Dealing with tantrums

Parents often learn to recognise warning signs of a temper tantrum. It is sometimes possible to stop the tantrum before it starts by using several approaches, such as:

  • trying to take their mind off the situation by doing or saying something unexpected or talking about a subject they are interested in
  • encouraging them to go to a quiet place for a few minutes and try some deep breathing or listen to soothing music
  • not putting ideas into their head by saying things like, "You’d better not have a tantrum about this"
  • remaining as cool and calm as possible (if you feel that your child’s frustration is directed at you, then your partner or another carer can take over the situation)

Once a tantrum has occurred, try and remain as calm as possible. If your child hurts themselves or others, you may need to be taught special restraint techniques. Your child's care team can advise you.

It is important not to give in to the demands that provoked the tantrums. While this may be tempting, it will give your child a signal that tantrums are an effective way of getting what they want. 

Food stealing

Many children with PWS will try to steal food if they get the opportunity. This is not because they are being naughty. Children with PWS are very bad at controlling their impulses when it comes to food. Often, they cannot help themselves from stealing food.

Nevertheless, food stealing is a behavioural problem that needs to be addressed, otherwise your child could become severely obese.

Tips to prevent food stealing include:

  • Try to establish a contract to reward good behaviour. In younger children, a verbal agreement, such as "If you stick to your diet then you can play an extra hour with your puzzles" should be sufficient. In older children and teenagers, a written contract may be more appropriate, especially as children with PWS respond well to clear instructions.
  • Most children with PWS will automatically lie about food stealing, even when the evidence is overwhelming. Rather than asking, "Did you steal that food?" say something along the lines of, "I know you stole that food and we need to talk about why that is wrong."
  • It is important that your child understands the consequences of their actions and what is considered acceptable behaviour. If they steal food or money to buy food from another person, always insist that they apologise and pay any money back.

Controlling the urge to steal food should always be highly praised and persistent good behaviour rewarded with treats.

Treatment for skin picking

Frequent skin picking can lead to scarring and infections of the skin such as cellulitis, an infection of the underlying tissue.

This may be a particular problem when it affects the legs. Reduced mobility and obesity reduce the drainage of blood from the legs, causing them to swell. This, along with diabetes, reduces the person’s ability to fight skin infection, and skin picking introduces the bacteria that cause the infection.

Once the skin has been damaged by cellulitis, it is susceptible to further infection. Therefore, it is very important to identify cellulitis early and get it treated with large doses of antibiotics.

It is recommended that you keep your child’s nails as short as possible. This should help minimise damage to the skin.

Keep any areas of damaged skin as clean as possible. If your child has a history of frequent skin infections, your child's care team may prescribe an antibiotic cream that you can use on damaged areas of skin to prevent infection.

Currently, two types of treatment are moderately effective in helping prevent people with PWS from picking their skin. These are cognitive behavioural therapy and medication.

Cognitive behavioural therapy

Cognitive behavioural therapy (CBT) is a type of talking therapy. CBT aims to change unhelpful and unhealthy patterns of behaviour by changing the way people think.

It is thought that people with PWS pick their skin as a way of coping with situations such as feeling unhappy and bored. CBT can help people understand the patterns of thought that drive the skin picking and try to find new ways of thinking about and coping with these situations, which do not involve skin picking.


The second treatment is to use selective serotonin reuptake inhibitors (a type of antidepressant) or antipsychotics (medications normally used to treat psychosis). However, these medications can cause a range of side effects and are not usually recommended for children under the age of 18.

It is likely that your child's care team would only consider prescribing medication if the symptoms of skin picking were severe enough to justify the risks associated with treatment.

Treatment for psychosis

A small number of people with PWS develop psychosis, usually during the teenage years or adulthood.

Psychosis means that a person has difficulties telling the difference between reality and their imagination. The symptoms of psychosis usually begin abruptly and will cause the affected person to suddenly become very upset and agitated and act in ways that are uncharacteristic.

If you notice a sudden and unusual change in your child’s behaviour, contact your child's care team.

Psychosis can be treated with medications such as antipsychotics and cognitive behavioural therapy. See the encyclopaedia A-Z topic on Psychosis – treatment for more information.

Treatment for other related conditions

Children and adolescents with PWS are vulnerable to a range of related conditions as they grow up. Find information on treating these conditions in the encyclopaedia A-Z by following the links below

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