Prader-Willi syndrome is a rare genetic condition that causes a wide range of physical symptoms, learning difficulties and behavioural problems. It's usually noticed shortly after birth.

Symptoms of Prader-Willi syndrome

Typical symptoms of Prader-Willi syndrome include::

  • an excessive appetite and overeating, which can easily lead to dangerous weight gain
  • restricted growth, (children are much shorter than average)
  • reduced muscle tone (hypotonia)
  • learning difficulties
  • lack of sexual development
  • behavioural problems, such as temper tantrums or stubbornness

Read more about symptoms of Prader-Willi syndrome.

What causes Prader-Willi syndrome?

Prader-Willi syndrome is caused by a fault in a group of genes on chromosome number 15. This fault leads to a number of problems and is thought to affect part of the brain called the hypothalamus, which produces hormones and regulates growth and appetite.

This may explain some of the typical features of Prader-Willi syndrome, such as delayed growth and persistent hunger.

The genetic mistake happens purely by chance, and boys and girls of all ethnic backgrounds can be affected.

It's extremely rare for parents to have more than one child with Prader-Willi syndrome.

Diagnosing Prader-Willi syndrome

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

Children may be recommended for genetic testing if they have the symptoms of Prader-Willi syndrome. Testing may be done in babies who are very floppy at birth.

Managing Prader-Willi syndrome

There's no cure for Prader-Willi syndrome, so treatment aims to manage the symptoms and associated problems. This includes managing the child's excessive appetite and behavioural problems.

One of the most important parts of caring for a child with Prader-Willi syndrome is to try to maintain a normal weight. The child should have a healthy, balanced diet, avoiding sweet treats and high-calorie items right from the start.

If children are allowed to eat as much as they want, they'll quickly become dangerously overweight. A child with the syndrome can eat 3 to 6 times more than other children of the same age and still feel hungry.

Limiting food intake can be very challenging for families. Children may behave badly to get extra food, and their hunger can make them hide or steal food.

Long-term problems caused by Prader-Willi syndrome

Prader-Willi syndrome itself isn't life-threatening. However, compulsive eating and weight gain can cause young adults with the syndrome to develop obesity-related conditions such as:

  • type 2 diabetes
  • heart failure
  • respiratory difficulties

If obesity is not prevented by controlling food intake, people with the condition are likely to die a lot younger than would normally be expected. If their diet is well controlled and they don't become overweight, adults can have a good quality of life and probably a normal life expectancy.

Many adults with Prader-Willi syndrome take part in activities such as voluntary or part-time work but, because of their behavioural problems and learning difficulties, it's unlikely they'll be able to live fully independent lives.

The increased appetite also means there is an increased risk of choking on food, so carers of a child with Prader-Willi syndrome are advised to learn what to do if someone is choking.


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.


Prader-Willi syndrome can cause a wide range of symptoms, and affect your child's physical, psychological and behavioural development.


Floppiness caused by weak muscles is usually noticed 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 1, and may need to be fed with a feeding tube (see managing Prader-Willi syndrome)

Poor sexual development

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 underdeveloped genitalia.

Children with Prader-Willi syndrome experience puberty later than usual and may not go through full development into an adult. For example:

  • boys may still have a high-pitched voice, and may not have much facial and body hair
  • girls often won't start their periods until they're in the 30s, and their breasts won't fully develop – 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. They are usually infertile because the testicles and ovaries do not develop normally. However, sexual activity is usually possible, particularly if sex hormones are replaced.

Distinctive features

Children with Prader-Willi syndrome have several distinctive features, including:

  • almond-shaped eyes
  • crossed eyes
  • a narrow forehead at the temples
  • narrow bridge of the nose
  • a thin upper lip and a downturned mouth
  • unusually fair hair, skin and eyes
  • small hands and feet

These features are usually noticed at or shortly after birth.

Increased appetite

Children with Prader-Willi syndrome develop an increased appetite and eat an excessive amount of food if they have the opportunity. The medical name for this is hyperphagia.

Between the ages of 1 and 4, the child will start to show an increased interest in food, ask for extra food and behave badly to get extra food. This behaviour increases during childhood and is seen in all children with Prader-Willi syndrome. It can include:

  • tantrums and angry behaviour to get food
  • interest in pictures of food, food-related play or discussion of food
  • hiding or stealing food, or stealing money to get food
  • eating inappropriate items, frozen or uncooked food, or waste food
  • very good memory for people who have given food to them in the past or situations where food was available

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
  • choking
  • a stomach rupture – where the stomach splits open, sometimes causing life-threatening infection

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.

Children with Prader-Willi syndrome don't always become obese and can remain slim if diet and food issues are controlled. They will never learn to control their food intake themselves and it must be managed for them.

They also have a slow metabolism, and require less food and fewer calories than other children of the same age. Reduced muscle tone means they are less physically active and don't burn off as much energy as other children.

Learning difficulties and delay in development

Most children with Prader-Willi syndrome have mild to moderate learning difficulties with a low IQ.

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 at around 24 months. Many are late to talk and have difficulty pronouncing some sounds.

Most children with Prader-Willi syndrome can attend a mainstream school with extra support, although some will move to a special school at secondary level

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 searches 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 2 years old.

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 people with Prader-Willi syndrome is 159cm (5ft 2in) for a man and 149cm (4ft 10in) 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 have difficult behaviour traits such as tantrums and stubbornness. Typical behavioural problems include:

  • temper tantrums and sudden rages, which can be triggered by minor events
  • 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
  • repeating the same activity (such as playing the same game or watching the same video repeatedly)
  • keeping a very strict daily routine – any unexpected disruption to the routine can upset them

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 4 out of 5 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 poo from their bottom. As well as causing embarrassment for children and parents, this can result in bleeding and infection.

Sleep problems

Many children with Prader-Willi syndrome have problems sleeping. They can become tired and sleep during the day but then wake during the night or very early in the morning.

Some children have interrupted breathing during sleep (sleep apnoea). These episodes cause excessive sleepiness in the day, which only worsens inactivity and obesity.

Sleep apnoea gets worse as you gain weight, leading to a vicious cycle. It can also be dangerous to have interrupted breathing at night.

It's important to identify sleep apnoea because effective treatment and support is available. Read more about treating sleep apnoea.

High pain and vomiting tolerance

Children with Prader-Willi syndrome have a high tolerance for 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 Prader-Willi syndrome.

Therefore, if a child with Prader-Willi syndrome does complain of pain, it should be taken seriously.

Abnormal curvature of the spine

Poor muscle tone means there is an increased chance of developing a curvature of the spine (scoliosis).

Other health problems

Children with Prader-Willi syndrome can develop:

  • eye problems – short or long-sightedness, or squint
  • poor muscle tone in the gut, which can cause constipation or a swollen tummy
  • tooth decay because they don't produce much saliva
  • weakening of the bones (osteoporosis) when they become adults because they don't have the sex hormones needed to keep bones healthy

Who can get it

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

Genes contain the instructions for making a human being. They're made up of DNA and packaged into strands called chromosomes. A person has 2 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 1 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 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 well as it usually does. This means that a person with the syndrome always feels hungry no matter how much food they eat.


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.

Read more about the causes of Prader-Willi 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 

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 recommended.


There's no cure for Prader-Willi syndrome, but your child will have support from healthcare professionals who will help you manage the problems.

Support for development will come from your local child development team, and your child will also see a hospital paediatrician or a paediatric endocrinologist.

The treatment plan will be continually reassessed as your child gets older and their needs change. The Prader-Willi Syndrome Association has detailed information about how the support your child needs will change as they get older.

Treating problems in babies

Poor feeding

Babies with Prader-Willi syndrome have difficulty feeding at birth, and may need to be fed using a tube that goes into their nose and down their throat into their stomach.

After a few months, it'll usually be possible to feed your child normally using breast or bottle milk, although they may be slower to feed than other babies. Dietitians and speech and language therapists can help with advice about what feeds to give and how to encourage your baby to feed.

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 because:

  • your son will have an increased risk of developing testicular cancer if the testicles aren't corrected
  • your son may have problems with his self-esteem and body image if he's "missing" one or both testicles

Managing weight and diet

The most important aspect of caring for a child with Prader-Willi syndrome is trying to manage their diet and prevent them gaining too much weight. It's also probably one of the biggest challenges.

Your child will never learn to control their food intake themselves, so you need to do this for them. Children with Prader-Willi syndrome burn up less energy, and need fewer calories and less food than other children. A children's dietitian can give you information about what food to give your child.

Advice about diet:

  • start to get into good habits with a healthy diet and regular mealtimes as soon as your child starts on solid food – don't wait for them to show signs of an increased appetite
  • avoid sugary items, sweets and high-calorie snacks
  • give smaller portions of carbohydrates such as potatoes, rice or pasta
  • increase the amount of lower-calorie items such as vegetables, salads and fruit
  • give a vitamin supplement

Your child will not learn to control their food intake themselves and you need to take control of things:

  • keep to regular mealtimes and do not allow any extra portions
  • stop them accessing food outside of mealtimes – you may need to lock cupboards and the fridge, or lock the kitchen – and make sure they can't get food from the bins or freezer
  • keep food out of their view
  • make sure there are no times they can access food unsupervised
  • make sure everyone who is in contact with the child (school staff, relatives and friends) knows about the issues with food

It's 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 have all been unsuccessful.

Weight loss surgery isn't recommended for children with Prader-Willi syndrome because they don't have the willpower to stick to the strict diet required after surgery.


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

Many children with Prader-Willi syndrome have reduced energy levels. 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 Prader-Willi syndrome usually prefer individual activities to team sports, such as:

  • swimming
  • walking
  • exercising in a gym

It's important not to promise food as a reward to encourage your child to participate in exercise because it can encourage unhealthy behaviour.

Hormone treatments

Treatment with an artificial version of the human growth hormone (HGH) is usually recommended for children with Prader-Willi syndrome.

HGH also has a number of other important health benefits. For example, it:

  • increases muscle size while lowering the amount of body fat
  • increases muscle strength, which helps with developmental progress such as walking and running
  • should increase energy levels, which will help your child become more physically active
  • helps normalise facial appearance, making the distinctive facial features associated with Prader-Willi syndrome less noticeable

It's usually recommended that treatment with HGH begins during early childhood, from 6 months to 2 years of age, and would normally carry on until the end of growth. A test looking for breathing problems (a sleep study) is normally done before starting growth hormone.

A type of HGH called somatropin is used to treat children with Prader-Willi syndrome. Somatropin is given by daily injection. Most children tolerate somatropin well and side effects are uncommon.

It's usual to replace female sex hormones (often with the combined oral contraceptive pill) to:

  • encourage development of secondary sex characteristics (breast development) and periods
  • improve bone strength and prevent osteoporosis

Replacing male sex hormone (testosterone) is more contentious. Although this will encourage development of puberty and build muscle strength, it's possible that some behavioural problems will be exaggerated.

Managing behavioural problems in children

Structure and routine

Most children with Prader-Willi syndrome cope best if they have a very structured environment and daily routine. For example, you should:

  • establish a regular daily routine and give plenty of notice if any changes are planned
  • 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 other people, such as relatives and teachers, are briefed about how to interact with your child
  • avoid eating in front of your child so they don't start to think about food

Dealing with tantrums

Parents often learn to recognise the warning signs of a temper tantrum. It's sometimes possible to stop the tantrum before it starts using a number of approaches. For example:

  • try to take their mind off the situation by doing or saying something unexpected, or talking about a subject they're interested in
  • encourage them to go to a quiet place for a few minutes and try some deep breathing or listen to soothing music
  • avoid saying things like, "You'd better not have a tantrum about this"
  • remain as cool and calm as possible – if you feel your child's frustration is directed at you, then your partner or another carer can take over the situation

After a tantrum, try to 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 will be able to advise you about this.

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

Taking food

Many children with Prader-Willi syndrome will try to take food if they get the opportunity. This isn't because they're being naughty but because they aren't able to control their impulses when it comes to food. Nevertheless, taking food is a behavioural problem that needs to be addressed, otherwise your child could become severely obese.

Tips to prevent stealing food include trying 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, particularly as children with Prader-Willi syndrome respond well to clear instructions.

Most children with the syndrome will automatically lie about taking food, even when the evidence is overwhelming. So 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's wrong."

It's important your child understands the consequences of their actions and what's considered acceptable behaviour. If they steal food or money to buy food, always insist they apologise and pay any money back.

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

The Prader-Willi Syndrome Association has also produced a leaflet about Behaviour management in Prader-Willi Syndrome (PDF, 144kb).

Treatment for skin picking

Frequent skin picking can lead to scarring and skin infections such as cellulitis, an infection of the underlying tissue. It's very important for cellulitis to be identified early and treated with large doses of antibiotics.

It's recommended you keep your child's nails as short as possible. This should help minimise damage to the skin. Try to keep any affected part of the body covered up and use clothes to limit access if possible.

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

Two types of treatment that are moderately effective in helping prevent people with Prader-Willi syndrome from picking their skin are cognitive behavioural therapy (CBT) and medication.

Cognitive behavioural therapy

CBT is a type of talking therapy. It aims to modify unhelpful and unhealthy patterns of behaviour by changing the way people think.

It's thought people with Prader-Willi syndrome pick their skin as a way of coping with situations such as feeling unhappy or bored. CBT can help people understand the thought patterns that drive skin picking and encourage them to find new ways of thinking about and coping with these situations.


A type of antidepressant – selective serotonin reuptake inhibitors (SSRIs) – or antipsychotics (medication usually used to treat psychosis) are sometimes recommended to treat Prader-Willi syndrome.

However, these medications can cause side effects and are not usually recommended for children under the age of 18.

Medication is usually only considered if the symptoms of skin picking are severe enough to justify the associated risks of treatment.

Treatment for psychosis

A small number of people with Prader-Willi syndrome develop psychosis, usually during the teenage years or adulthood.

Psychosis is a mental health problem that causes people to perceive or interpret things differently from those around them. The symptoms of psychosis usually begin abruptly and will cause the person affected to suddenly become very upset and agitated, and act in ways that are uncharacteristic.

Contact your child's care team if you notice a sudden and unusual change in their behaviour.

Psychosis can be treated with CBT or medication such as antipsychotics.

Adults with Prader-Willi syndrome

Most adults with Prader-Willi syndrome are unable to live fully independent lives, such as living in their own home and having a full-time job because their behavioural issues and problems with food mean these environments and situations are too demanding.

However, adults with Prader-Willi syndrome can have active social lives and become involved in clubs or volunteering. Adults with the syndrome who don't live with their parents will probably require residential care.

The information on this page has been adapted by NHS Wales from original content supplied by NHS UK NHS website nhs.uk
Last Updated: 13/07/2021 14:16:31