Prader-Willi syndrome

Symptoms of Prader-Willi syndrome

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


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 managing Prader-Willi syndrome)

Poor sexual development

Another feature that becomes apparent after birth is hypogonadism. Hypogonadism means 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 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 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. Therefore, they can eat objects that would make other people very ill. This means they are at higher risk of food poisoning and choking.

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. Lack of muscle tone contributes to them being 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 a life-threatening infection.

It is thought that as many as one 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 with a low IQ. This is usually in the range of 50-85, which is moderate to borderline intellectual disability.

This means 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 word search puzzles and jigsaws.

Read more information about learning disability.

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.

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

If HGH is not replaced, 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 managing Prader-Willi syndrome).

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 bottom. 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 saliva, which can cause tooth decay
  • skin that is 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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