Prader-Willi syndrome

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 syndrome that 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.

Read more about learning disability.

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. Read more about treating sleep apnoea.

Other features

Other features of Prader-Willi syndrome can include:

  • unusually fair hair, skin and eyes
  • small hands and feet
  • narrow hands
  • crossed eyes
  • short-sightedness 
  • long-sightedness 
  • 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.

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