Prader-Willi syndrome: symptoms, causes, diagnosis and care

Prader-Willi syndrome is a rare genetic condition that the NHS says causes a wide range of physical symptoms, learning difficulties and behavioural challenges. Prader-Willi Syndrome Association UK (PWSA UK) describes it as a rare, complex genetic disorder that affects males and females from birth and throughout their lives. It causes low muscle tone with delays in motor development, mild to moderate learning difficulty, incomplete sexual development and emotional and social immaturity.

PWSA UK says that during childhood an overwhelming, insatiable chronic appetite usually develops, which without rigorous food management and exercise leads to food seeking, stealing and life-threatening obesity.

Symptoms change with age. The NHS says floppiness caused by weak muscles (hypotonia) is usually noticed shortly after birth, and a baby may have a weak cry, poor reflexes, not a full range of movement and be unable to suck properly, so may have feeding difficulties and need a feeding tube. After a few months it is usually possible to feed normally, though they may be slower.

Between the ages of 1 and 4, the NHS says a child will start to show increased interest in food and become frustrated when they cannot get extra food. Children are usually much shorter than others of their age, apparent by about 2 years, partly because of low levels of human growth hormone and no typical growth spurt in puberty.

The NHS says people with PWS develop an increased appetite, known as hyperphagia, and eat an excessive amount if they have the opportunity. They can eat much more than other people and still feel hungry. Food can be a trigger for challenging behaviour, such as hiding or stealing food, or eating inappropriate items.

The NHS says the most important aspect of care is managing diet and preventing too much weight gain, which is also one of the biggest challenges. People with PWS burn less energy and need fewer calories than others, and cannot control their own food intake, so it must be managed for them.

• Start healthy habits and regular mealtimes as soon as solid food starts, without waiting for appetite to increase.

• Avoid sugary items, sweets and high-calorie snacks; give smaller portions of carbohydrates such as potatoes, rice or pasta; increase vegetables, salads and fruit; give a vitamin supplement.

• Keep to regular mealtimes with no extra portions, and stop access to food outside mealtimes, which may mean locking cupboards, the fridge or the kitchen, and securing bins and freezers.

• Keep food out of sight, avoid eating in front of the child and tell relatives, teachers and friends about the restrictions.

• Do exercise: the NHS says children should do at least 60 minutes a day, which can be broken into 5- to 10-minute sessions, and food should not be offered as a reward.

The NHS says PWS is caused by a genetic change on chromosome 15. A person normally has 2 copies of chromosome 15. Around 70% of cases are the result of missing genetic information from the copy inherited from the father, called paternal deletion. This is thought to happen entirely by chance, so it is practically unheard of to have more than 1 child with PWS caused by paternal deletion. The NHS says that if PWS is caused by a different type of change on chromosome 15, there is a very small chance of having another child with the syndrome.

The NHS says the problem with chromosome 15 is thought to disrupt the development and functioning of the hypothalamus, a part of the brain that produces hormones and helps regulate appetite, which may explain delayed growth and persistent hunger.

The NHS says PWS can usually be diagnosed using genetic tests on a sample of the child's blood, which check chromosomes for the changes known to cause it. As well as confirming the diagnosis, the results help families work out the likelihood of having another child with PWS. Babies who are very floppy at birth may also be tested.

A checklist of typical symptoms is used to identify which children should be tested. The NHS says a child under 3 who scores 5 points with at least 4 major criteria, or a child over 3 who scores 8 points with at least 5 major criteria, is strongly suspected of having PWS and genetic testing is recommended. PWSA UK adds that a few people with a diagnosis do not have the typical physical features, for example they may be taller than most.

The NHS says there is no cure, but a child will have support from the local child development team, and will see a hospital paediatrician or paediatric endocrinologist, with the plan reassessed as they grow. PWSA UK says there are a number of NHS-run PWS clinics across the UK, run by endocrinologists with a special interest in PWS.

Growth hormone: the NHS says treatment with an artificial version of human growth hormone is usually recommended for children, starting during early childhood from 6 months to 2 years and normally continuing to the end of growth, with a sleep study usually done first. The NHS says it increases muscle size while lowering body fat, increases muscle strength and should increase energy levels. PWSA UK says it is not currently licensed in the UK for adults with PWS, although a few individuals may receive it.

Other treatments: the NHS says surgery is usually recommended for undescended testicles in the first or second year of life, female sex hormones are often replaced to encourage development and improve bone strength, and replacing testosterone is more contentious because behavioural challenges may get worse. Medicines tried to suppress appetite have been unsuccessful, and weight loss surgery is not recommended because people cannot stick to the strict diet required afterwards.

For skin picking, the NHS suggests keeping nails short, covering affected areas and keeping damaged skin clean, with CBT and sometimes medicines being moderately effective. For behaviour, a structured routine, plenty of notice of change and calm responses help.

The NHS says people with PWS can tolerate much larger amounts of food before the body automatically vomits, and are not as sensitive to pain, so they are at higher risk of food poisoning, choking and stomach rupture. Vomiting and stomach pain are the 2 most common signs of gastric rupture. People with PWS do not usually vomit or complain about stomach pain, so the NHS says to take these symptoms very seriously and call your care team or GP immediately.

PWSA UK says serious illness or injury may be masked: a high pain threshold means people may not complain of pain, they may not develop a high temperature in infection, and vomiting is not a good guide to illness. It says binge-eating episodes need close supervision and emergency medical care if in doubt, and that emergency services should be told about the association with PWS. The NHS advises carers to learn what to do if someone is choking.

If someone with PWS collapses, has sudden severe tummy pain or you suspect a binge-eating episode with danger signs, call 999 and say that the person has Prader-Willi syndrome.

The NHS says most people with PWS have mild to moderate learning difficulties with a low IQ. Most children can attend a mainstream school with extra support, although some will move to a special school at secondary level. They usually have short-term memory problems but often a good long-term memory, and tend to be good at puzzles such as word searches and jigsaws.

Behaviour can be challenging at times, and the NHS lists unexpected change, frustration, anxiety around food, feeling under pressure, lack of structure, too much stimulation, low mood and other undiagnosed conditions such as autism as triggers. It also says people with PWS are affectionate, kind, caring and funny. A small number develop psychosis, usually in the teenage years or adulthood, and the NHS says to contact the care team about a sudden unusual change in behaviour.

Many people with PWS have sleep problems, and some have interrupted breathing during sleep (sleep apnoea), which the NHS says is important to identify because effective treatment is available.

The NHS says PWS itself is not life-threatening, but compulsive eating and weight gain can lead young adults to develop serious conditions such as type 2 diabetes, heart failure and breathing difficulties. If diet is well controlled and weight stays healthy, adults can have a good quality of life and probably a normal life expectancy.

Most adults are unlikely to be able to live fully independent lives because of behaviour and food issues, but can have active social lives and take part in volunteering, part-time work and clubs. Adults who do not live with their parents may need residential care or supported living, the NHS says.

On the NHS, a baby who is very floppy or a child with typical features is usually seen by a paediatrician and tested through genetic services, and the NHS says clinical teams pass information to the National Congenital Anomaly and Rare Disease Registration Service, which families can opt out of at any time. PWSA UK says NHS-run PWS clinics exist across the UK.

Some families also choose to see private specialists for second opinions or therapies. If you do, share the findings with your NHS care team so that growth hormone, diet and monitoring plans stay coordinated. PWSA UK offers information for families, carers and professionals, and the NHS signposts it for support.