All about Prader-Willi Syndrome (2024)

Prader-Willi syndrome (PWS) is a rare, complex genetic disorder that affects both males and females from birth and throughout their lives. The condition causes a wide range of physical symptoms, learning difficulties and behavioural challenges.

Andrea Prader and Heinrich Willi, two Swiss paediatricians, first described the syndrome in the 1950s when they identified similarities among a set of nine individuals seen at their clinic. These commonalities led them to the conclusion that this syndrome, later to be called “Prader-Willi syndrome”, was distinct from other clinically overlapping disorders.

Those with Prader-Willi syndrome have a genetic defect on chromosome number 15. In around 70% of cases, some of the DNA information that is inherited from the father is missing, which is referred to as “paternal deletion”. This is usually not detectable with routine genetic analysis such as amniocentesis.

Around 30% of other cases occur when a child has two copies of chromosome number 15 from their mother and none from their father. This scenario is termed maternal uniparental disomy (UPD).

Finally, in a very small percentage of cases, about 1%–3%, a small genetic mutation in the Prader-Willi region causes the paternal chromosome 15 genetic material, although present, to be inactive.

The condition is obtained purely by chance, but those who have one child with PWS have a less than 1% chance of any future children being affected. However, if twins are identical, both will have PWS. If they are non-identical, then one could have PWS and one not.

The PWS region of chromosome 15 is one of the most complex regions of the human genome. Although there have been significant advances in understanding and characterising the genetic changes associated with PWS, the exact mechanism by which lack of functional genetic material in this region leads to the symptoms associated with PWS is not understood.

Scientists are actively studying the normal role of the genetic sequences in the PWS region and how their loss affects the hypothalamus, a structure deep in the brain that acts as the body’s smart control coordinating centre, and other systems in the body.

Scientists do not know what increases the risk for Prader-Willi syndrome. The genetic error that leads to Prader-Willi syndrome occurs randomly, usually very early in foetal development with decreased foetal movements and growth restriction. The syndrome is usually not hereditary.

Prader-Willi syndrome-like symptoms can be “acquired” by damage to the hypothalamus during a person’s life, such as head injury or surgery, or from a dysfunction of the hypothalamus. In these cases, the person does not have any of the genetic abnormalities and few of the physical characteristics of PWS, but acquires some or all of the behavioural and appetite problems which are associated with the syndrome. This condition is known as Acquired Prader-Willi syndrome.

Prader-Willi syndrome causes life-threatening obesity in children. The syndrome affects many aspects of the person’s life, including eating, behaviour and mood, physical growth, and intellectual development. It affects the individual in different ways at various stages of their life.

Babies with Prader-Willi syndrome are very floppy at birth (hypotonia), and their ability to suck is weak or absent. Tube-feeding may be required for the first few days or weeks of life and breastfeeding is rarely initially successful.

Babies show little interest in feeding during the first few months of their lives, have a very weak cry, and sleep for most of the time during the early weeks. Male babies may have noticeably underdeveloped genital organs. Female babies may also have underdeveloped genitalia, but this is much harder to detect.

Developmental milestones such as sitting, standing, walking and talking are generally delayed, but most children with PWS are able to attain all these abilities by the time they are about five years old. Often, infants with PWS are very lovable and placid, and seem to draw admiration wherever they go.

Sometime between the ages of one and four years, most children with Prader-Willi syndrome begin to show a heightened interest in food, although some do not show this interest until they are older than four, and in severe cases develop what appears to be an insatiable appetite, so that they may try to obtain food by any means possible.

The degree to which this occurs varies considerably between individuals, but there is always a preoccupation with food in play and talk. This can be helped by good management, dietary control and educating the child about their diet. Children with PWS are generally placid and friendly, but may begin to exhibit stubborn or obsessive behaviour and outbursts of temper if they cannot get their own way or are denied access to food. Each child with PWS is individual; some will go to mainstream schools, some to specialist schools and some will start at mainstream and transfer to a special school later on.

Teenagers with Prader-Willi syndrome who have not received growth hormone do not experience the growth spurt which usually occurs in the early teens and so tend to be a few inches shorter than average: men average about 5’2” (155cm) and women average about 4’10” (145cm). However, those on growth hormone very often reach at least the same height as their parents. Sex hormones (both male and female) can help with sexual development, but this will depend to some extent on the individual’s existing hormone levels.

Pubic and facial hair may be scanty, and voice change may not occur in puberty. In women, breast development is often small, and menstruation, if it occurs, may be irregular. Behavioural and eating problems may become more challenging during the teens and early twenties. Individuals with PWS do attend colleges, and some do work experience and voluntary work.

As adults, people with Prader-Willi syndrome have varying abilities in attaining independence, although all will need some form of support or monitoring to help with controlling their food intake, and therefore their weight.

Despite the fact that many individuals have the intellectual and physical ability to work, they are usually ill-equipped on an emotional and social level to deal with the stresses and demands of the ordinary workplace. However, they can make a positive contribution to society in many ways and may be involved in voluntary work and craft work or have a part-time job. Many people live with their families, but an increasing number, including Harvey Price, are living in residential homes, or being supported to live in the community.

Life expectancy for those with Prader-Willi syndrome varies because of health problems associated with massive obesity which can shorten life expectancy. With better dietary management and better understanding of the problems associated with PWS, life expectancy can increase. The oldest known person with PWS in the UK was a woman who died at the age of 74.

• Hypotonia – This is weak muscle tone, and floppiness at birth.
• Hypogonadism – This is immature development of sexual organs and other sexual characteristics.
• Obesity – This is caused by excessive appetite and overeating (hyperphagia), and a decreased calorific requirement owing to low energy expenditure levels, although obesity is not normally a feature of those whose food intake is strictly controlled.
• Central nervous system and endocrine gland dysfunction – Causing varying degrees of:
  – Learning disability – Some people have recorded IQs of 90 or above, whilst a minority have severe learning difficulties. The average IQ for people with PWS is around 60–70.
  – Short stature.
  – Hyperphagia.
  – Somnolence (excessive sleepiness).
  – Poor emotional and social development.
• Poor large muscle strength – Often coupled with poor coordination and balance; their small muscle strength is usually better.

Many people with PWS also exhibit characteristic facial and other physical features.

These include:

• Almond-shaped eyes.
• A narrow forehead (measured across).
• A down-turned mouth with…
• A triangular-shaped upper lip.
• Small hands and feet.

The main complications of Prader-Willi syndrome are compulsive eating and weight gain which can lead to obesity-related conditions such as type 2 diabetes, heart failure, and breathing difficulties.

Individuals with Prader-Willi syndrome frequently have a decreased sensitivity to pain and so there is a potential danger of underestimating a problem. As PWS babies may have a weak cry, they may not be able to let you know if they are experiencing pain.

Skin picking or spot picking is very common in PWS. Skin picking is often triggered by small spots and grazes, which are picked continually, and so never allowed to heal. However, sometimes wounds are made where there was no wound previously. Any area of the body can be a target. Most common are the limbs and the head or face, but other areas may be involved. There is an increased risk of infection as a result.

There is a risk of choking arising from people with PWS trying to eat food quickly, either because they habitually do this, or because they are trying to disguise the fact that they have taken food to eat which they should not have done.

Other potential health problems and/or complications for those with PWS can include:

• Scoliosis.
• Osteoporosis in both males and females, at a young age due to a lack of sex hormones.
• Cellulitis.
• Vitamin D deficiency.
• Challenging behaviours, whether or not the person has a learning disability.

More than 70% of children and adolescents with Prader-Willi syndrome have a high risk of developing autism spectrum disorder (ASD), according to a study in Chinese patients.

The findings also indicated that individuals who were shorter, had excess weight, and experienced obstructive sleep apnoea, a condition in which the airways become constricted during sleep, a common problem in PWS, were at a higher risk of developing ASD.

The most important aspect of caring for someone with Prader-Willi syndrome is trying to manage their diet and preventing them from gaining too much weight. It is also probably one of the biggest challenges. If energy intake has not been carefully monitored, weight gain is rapid, so a lower calorie diet is essential throughout the person’s life.

An appropriate exercise programme helps to keep weight levels down and also improves muscle strength. If weight is not controlled, fat accumulates in a characteristic way on the buttocks, stomach, lower trunk and thighs.

Most people with Prader-Willi syndrome cope best if they have a very structured environment and daily routine, where food access is controlled, boundaries are clear and a consistent approach is adopted by everyone involved.

People with PWS are much more vulnerable to stress than the general population. Generally speaking, they have a low tolerance for anxiety and frustration.

Some of the more general triggers, not only for challenging behaviour but also for emotional outbursts of any kind, can include:

• Anxieties around food.
• Presence of food in the room or nearby.
• Frustration at not being able to do what they want to do.
• Communication or speech and language problems.
• Feeling under pressure.
• A “chaotic” environment with too much stimulus and/or too little structure.
• Change of any kind.
• Harsh tone and punitive attitudes from others.

Being aware of potential triggers and how to avoid them can help to stabilise their behaviour. Do not argue with a PWS person as this will only escalate or prolong the incident. Threats and bribery are also ineffective.

After an incident, the person with PWS will usually need time to recover their equilibrium, so provide a calm, low-stimulating space, where they can go and lie or sit quietly. Many often go to sleep.

Teaching those with PWS coping skills and behavioural relaxation techniques can help to prevent them from going into meltdown.

These skills include:

• Deep breathing.
• Stress relief through sensory balls.
• Listening to music.
• Learning how to communicate feelings appropriately.
• Taking a break.

Prader-Willi syndrome can usually be confirmed by carrying out genetic testing to check the chromosomes in a sample of the child’s blood for the genetic changes known to cause Prader-Willi syndrome.

Genetic testing may be recommended if a child has any of the symptoms of PWS. Babies who are very floppy at birth may also be tested. Over the last 10 years, the age of diagnosis has fallen significantly and the majority of cases are now diagnosed during the first months of life, allowing the earlier introduction of treatments to reduce the morbidity, in particular by preventing obesity.

There is no cure for Prader-Willi syndrome, but people with the disorder can benefit from a variety of treatments to improve their symptoms. The treatment plan will be continually reassessed as the child gets older and their needs change.

Characteristics and symptoms of Prader-Willi syndrome can vary considerably between individuals. Growth hormone (GH) treatment is recommended to be started by the age of 12 months, and should continue until the child has stopped growing, although it may not be suitable in all cases. A specialist will decide when to start GH treatment for a child with PWS. Some individuals benefit from various other hormone treatments and surgical interventions such as surgery to bring down undescended testes.

No drug so far has proved to be of lasting help with regard to suppressing appetite. However, many of the adverse effects of the syndrome can be lessened by good dietary management, exercise programmes, good general healthcare, and by good general management of behaviour and education.

Other treatments to help manage the symptoms of the condition include:

• Paediatric dietitian for dietary advice.
• Physiotherapy for muscle tone and core strength.
• Speech and language therapy to help with communication.

The Prader-Willi Syndrome Association (UK) is the only organisation in the UK which is dedicated to supporting people with Prader-Willi syndrome (PWS), their families, carers, and the professionals who work with them. It offers a range of services to help families and people with PWS.

Other useful contacts include:

• The National Autistic Society Call 0207 833 2299
• Diabetes UK helpline 0345 123 2399