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Prader Willi syndrome

Prader Willi syndrome

First described in 1956 by Swiss doctors, Prader-Willi syndrome is a complex genetic condition that affects several different parts of the body. If you haven’t heard of Prader-Willi syndrome it’s because it’s not exactly common. However, if you are already aware of it, you’ll probably remember one of the problems it causes more than any of the others – namely an excessive appetite. 


What is Prader Willi syndrome?

Prader-Willi is a syndrome that causes hyperphagia, which is the medical term for an increased appetite and overeating. And while Prader-Willi syndrome itself isn’t life threatening, it can lead to a range of health problems related to obesity if the compulsive hunger and eating it causes aren’t strictly managed.

How common is Prader Willi syndrome?

Experts aren’t really sure exactly how many people are affected by Prader-Willi syndrome. According to the Prader-Willi Syndrome Association UK (PWSA UK) this uncertainty is probably caused by the fact that Prader-Willi syndrome may still go undiagnosed in some people, especially older adults, and also because there’s no central UK register of people living with rare genetic syndromes (i).

  • PWSA UK says a study of a single health region in the UK has estimated between one in 22,000 and one in 52,000 children are born with Prader-Willi syndrome in this country (i).

  • The Manchester Centre for Genomic Medicine suggests one in every 15,000 births is affected by Prader-Willi syndrome, which equates to around 35 children born with the condition in the UK each year (ii).

  • The US National Library of Medicine estimates Prader-Willi syndrome affects between one in 10,000 to 30,000 people worldwide (iii).

To put all of this into context, the incidence of Down syndrome – another genetic syndrome – is far lower at around one in 715 births (i). Meanwhile Prader-Willi syndrome is thought to affect males and females equally, including people of any ethnic background.
Thankfully these days someone with Prader-Willi syndrome can have a good quality of life and a near-normal life expectancy if their diet and weight are managed effectively (according to PWSA UK the oldest known person with Prader-Willi syndrome in the UK died at the age of 74 (i)). However, it’s unlikely for them to live independently as adults, plus they’ll need medical supervision throughout their lives.

What causes Prader Willi syndrome?

Prader-Willi syndrome is the result of a problem with your genes, specifically some of the genes on chromosome 15.
We all have 23 pairs of chromosomes, which are strands of genes made up of DNA. One of the chromosomes that belongs to the 15th pair is different in people with Prader-Willi syndrome. Currently, experts believe there are four different genetic abnormalities on chromosome 15 that cause Prader-Willi syndrome:

  1. A small part of chromosome 15 inherited from the father is missing (this is known as a deletion) – this abnormality is thought to affect up to 70 percent of cases of Prader-Willi syndrome (iv).

  2. Up to 30 percent of Prader-Willi syndrome cases may be caused by maternal diosmy, which is when both chromosomes in a pair (in this case chromosome 15) come from the mother (normally each pair is made of one chromosome from each parent) (iv).

  3. Translocation – an exchange of material between or within chromosomes – involving chromosome 15 is rarer, causing less than five percent of Prader-Willi syndrome cases (iv).

  4. An imprinting error on chromosome 15 – this causes genetics similar to that of maternal disomy.

Of these four different types of genetic abnormalities, only two – translocation and an imprinting error – are likely to result in families having more than one child with Prader-Willi syndrome. Indeed, PWSA UK claims that in the vast majority of cases the risk of having another child with Prader-Willi syndrome is very slight (iv). Experts believe the majority of cases are not inherited because the genetic changes happen randomly while reproductive cells are being formed or during the early development of the embryo (iii).


Why are people with Prader-Willi syndrome always hungry?

Excessive appetite and a constant craving for food are classic signs of Prader-Willi syndrome. It’s thought this may happen because the genetic abnormalities on chromosome 15 affect part of the brain called the hypothalamus, which is involved in regulating appetite as well as growth. So as well as explaining why people with Prader-Willi syndrome are often always hungry, it could account for the fact that they also tend to experience delayed growth (see below).


Prader Willi syndrome symptoms

Chronic overeating and weight gain are common in Prader-Willi syndrome, but there are several other symptoms too. Some of these often affect someone born with Prader-Willi syndrome at different ages.

Prader Willi syndrome symptoms in babies

The first sign that a child between the ages of 0 to 12 months may have Prader-Willi syndrome is weak and floppy muscles, which is usually noticed shortly after they’re born. Called hypotonia in the medical world, this can cause feeding problems because it means a baby cannot suck properly. As a result, they may experience poor weight gain during the first year of their lives and may even have to be fed via a feeding tube. Other problems caused by weak muscles include poor muscle reflexes, a limited range of movement and a weak cry.
Babies born with Prader-Willi syndrome often also experience problems with sexual development. For instance, male babies may have undescended testicles, where one or both of their testicles is still inside their abdomen. Female babies can also have underdeveloped genitals, though this is usually harder to spot.

Prader Willi syndrome facial features

Prader-Willi syndrome usually causes distinctive facial features that are often noticed shortly after a baby is born, such as:

  • Narrow face

  • High, narrow forehead

  • Almond-shaped eyes

  • Thin upper lip 

  • Small, turned-down mouth

  • Narrow bridge of the nose

  • ‘Wandering’ or ‘crossed’ eyes (strabismus)

  • Small hands and feet

  • Very fair skin, hair and eyes (hypopigmentation)


Prader Willi syndrome symptoms in children

Some time after their first birthday, most children with Prader-Willi syndrome develop a preoccupation with food and an increased appetite (usually this happens between the ages of one and four years, though in some children it develops a little later). They crave food constantly and, if left to their own devices, may frequently eat huge amounts of food (people with Prader-Willi syndrome can eat far more food than normal before their body automatically vomits it back up).
How much this affects individuals with Prader-Willi syndrome varies greatly, however it can be the biggest challenge for parents as a child with Prader-Willi syndrome will often demand extra food and become frustrated when they can’t get what they want. They may use problem behaviours to get more food – getting angry or having temper tantrums, for instance – or they may hide or steal food or steal money to buy food.
People with Prader-Willi syndrome may also eat food that others wouldn’t eat, such as frozen food before it’s thawed, raw food before it’s cooked, food past its expiry date and waste food. As a result, they have a higher risk of having food poisoning and choking, plus they may experience a stomach rupture (this can cause a life-threatening infection).
The main risk, however, is that a child with Prader-Willi syndrome will gain weight and become obese. Overeating isn’t the only factor involved, as children with Prader-Willi syndrome tend to have a slow metabolism, which means they need less food and fewer calories than others. They are often also less physically active than other children, thanks to the problems they have with poor muscle tone, and burn off less energy. And then if they do become obese, they will also develop a higher risk of problems related to obesity, such as type 2 diabetes, heart disease and stroke.
Other symptoms that can develop in children with Prader-Willi syndrome include poor growth and strength (this is often caused by low levels of growth hormone). For instance, children with Prader-Willi syndrome tend to be shorter than their peers, an issue that usually becomes noticeable by the time they reach two years old (v). 

Is Prader-Willi a form of autism?

Studies suggest some children with Prader-Willi syndrome can also experience symptoms of autism spectrum disorder, leading experts to believe the two conditions may sometimes happen at the same time (vi). Some common autism symptoms seen in children with Prader-Willi include (vii):

  • Repetitive and compulsive behaviours such as skin picking, ritualized eating,  hoarding, ordering and arranging, repeated checking and excessive washing

  • Social and communicative impairment (problems getting along with other people)

  • Developmental delays often happen in babies and young children with Prader-Willi syndrome as well as those who have autism. Delayed motor skill development can include sitting, standing, walking and talking – though most children with Prader-Willi syndrome are thought to reach these milestones by the time they’re five years old (i). On the other hand, according to the NHS people with Prader-Willi syndrome tend to be good at solving puzzles such as jigsaws and word searches (viii).

  • Reduced cognitive development, which may lead to learning disabilities.


Prader Willi syndrome symptoms in teenagers

Puberty in most children with Prader-Willi syndrome is delayed until the late teens. Other problems with sexual development may include a small penis and undescended testicles in males, with small breast development and irregular or infrequent periods in females.
Without medication children with Prader-Willi syndrome usually don’t experience a growth spurt in their early teens, so they tend to be shorter in height than other teenagers. Indeed, without medication the average height for adult men with Prader-Willi syndrome is about 159cm (5ft 2in), while adult women with Prader-Willi syndrome reach an average of 149cm (4ft 10in) (v). 

Prader Willi syndrome symptoms in adults


Other symptoms and health problems that can develop both in childhood and during adulthood include:

  • Skin picking (scratching and pulling at their skin), which can cause bleeding and infection

  • Sleep apnoea (interrupted breathing during sleep) and other sleep problems

  • High pain tolerance (also high tolerance to vomiting)

  • Vision problems such as long or short-sightedness

  • Tooth decay caused by a lack of saliva

  • Osteoporosis caused by a lack of sex hormones

  • Constipation or a swollen stomach, caused by poor muscle tone in the gut

  • Scoliosis (curvature of the spine)

Nearly all adults with Prader-Willi syndrome continue to need help and support with controlling how much they eat and their weight throughout their lives. The degree of independent living they can achieve, however, will vary from one adult with Prader-Willi syndrome to another, with many living with their families and others living in residential homes or being supported by the community.

Prader Willi syndrome symptoms diagnosis

Genetic testing can confirm whether a child has Prader-Willi syndrome. If the test result is positive, you and your child will get help and support from healthcare professionals to manage their condition. 

Can Prader Willi syndrome be cured?


There is no cure for Prader-Willi syndrome but there are some treatments that can help with some of the symptoms. These include:

  • Treatment for undescended testicles (this is usually performed before a male baby’s second birthday and can reduce their risk of developing testicular cancer later in life)

  • Human growth hormone treatment, which can help with muscle size and strength as well as a child’s height (according to PWSA UK children taking growth hormones often reach at least the same height as their parents (i))

  • Sex hormone treatment for females with Prader-Willi syndrome to encourage the development of a more regular menstrual cycle as well as breast development, plus improve bone strength and reduce the risk of osteoporosis (sex hormone treatment isn’t as frequently recommended for males with Prader-Willi syndrome, however)

  • Cognitive behavioural therapy and antidepressant medication to help with skin picking


Living with Prader Willi syndrome

In the majority of cases, the biggest challenge of having a child with Prader-Willi syndrome will be to manage their diet and weight. Your healthcare team will include a dietitian who can help you with this aspect of your child’s care. Some of the advice they might give you to help them maintain a healthy weight may include the following:

  • Avoid giving your child high-calorie sugary foods or drinks

  • Make sure they get plenty of fruit and vegetables that are lower in calories

  • Give them small portions of carbohydrate foods (bread, rice, potatoes and pasta) and fatty foods (try to give them low-fat alternatives where possible)

  • Schedule regular mealtimes and stick to them as often as you can

  • Outside of mealtimes try to keep all food out of their sight (you may also have to lock your food cupboards, fridge and freezer to stop them accessing food)

  • Make sure everyone they come into contact with – including friends, family members, neighbours, teachers etc – knows about their issues with food

According to the NHS one of the things you could also do is to give your child a vitamin supplement (vi). Look for a good-quality multivitamin and mineral supplement that’s formulated for your child’s age group that provides all the important nutrients they need to support their physical and mental health. You may also find it useful to give them a sugar-free chewable multivitamin or a supplement that dissolves in water to make a tasty fizzy drink.
Supplements that contain omega-3 essential fatty acids, such as fish oil supplements, may also help support your child’s overall growth and development. Again, look for a supplement that’s suitable for your child’s age, and if they don’t like swallowing tablets try giving them a chewable supplement with a taste they’ll like.
It’s also important to encourage your child to stay active, though this too can be a challenge since many people with Prader-Willi syndrome have less energy than others. Your healthcare team will help you to establish an exercise plan that will suit your child, often one that includes activities they can do by themselves as people with Prader-Willi syndrome often prefer these to group activities (team sports, for instance).

What is the life expectancy for Prader-Willi syndrome?

Prader-Willi syndrome used to be associated with limited life expectancy because of the health problems it can cause in relation to obesity. These days things are very different, thanks largely to the fact that we now know and understand more about the condition and the problems it can trigger and because the diet and weight management of those affected can be managed more effectively. However, it still remains a challenging condition for both those who are directly affected and their families, largely because of the physical symptoms, learning difficulties and behavioural problems it comes with.

Find out more

You can find out more information and get support from PWSA UK online or by calling the charity’s helpline on 01332 365676. Meanwhile there’s lots more advice and information about a range of health conditions in our pharmacy health library


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  6. , Autism spectrum disorder in Prader-Willi syndrome: A systematic review. Am J Med Genet A. ;167A(12):2936-44. Available online:

  7. , , . Prader-Willi syndrome and autism spectrum disorders: ann evolving story. J Neurodev Disord. ;3(3): 225-237.Available online:

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Disclaimer: The information presented by Nature's Best is for informational purposes only. It is based on scientific studies (human, animal, or in vitro), clinical experience, or traditional usage as cited in each article. The results reported may not necessarily occur in all individuals. Self-treatment is not recommended for life-threatening conditions that require medical treatment under a doctor's care. For many of the conditions discussed, treatment with prescription or over the counter medication is also available. Consult your doctor, practitioner, and/or pharmacist for any health problem and before using any supplements or before making any changes in prescribed medications.

Our Author - Christine Morgan


Christine Morgan has been a freelance health and wellbeing journalist for almost 20 years, having written for numerous publications including the Daily Mirror, S Magazine, Top Sante, Healthy, Woman & Home, Zest, Allergy, Healthy Times and Pregnancy & Birth; she has also edited several titles such as Women’ Health, Shine’s Real Health & Beauty and All About Health.

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