The main characteristics of Prader-Willi syndrome (Clinical diagnostic criteria can be found on the ‘Diagnosis’ page.)

Physical characteristics in newborns:

Hypotonia (low muscle tone) – most babies are very floppy as newborns with a poor suck reflex and weak cry.

‘Failure to thrive’ – low birth weight followed by slow weight gain / growth, typically with feeding difficulties.

Distinct facial features – almond shape eyes, narrowing of the head at the temples, a turned down mouth and thin upper lip (more likely in those with a deletion.)

Hypogonadism (underdeveloped sex organs) – includes undescended testes which are typical in boys, but can be brought down with a simple operation.

Excessive sleepiness and showing little response to stimulation.

Fair colouring (hair, eyes, skin) compared to other members of the family (also more likely in those with a deletion.)

Small hands and feet.

Possible lack of eye coordination (strabismus / squint).

Possible congenital hip dislocation.

Characteristics that may become evident as they become older:

Hyperphagia (increased appetite), preoccupation with food, excessive or rapid weight gain.

Delayed motor and speech development, ongoing oral-motor and / or articulation difficulties.

Borderline / mild intellectual disability is most common, but some children score in the moderate intellectual disability range, whereas others score within the borderline to low-average ranges of normal intelligence in cognitive testing.

Specific learning disabilities, i.e. processing delay, deficits in short term memory, language comprehension, abstract thinking and executive functioning.

Incomplete puberty and infertility (hormone replacement treatments, such as testosterone, may be given to help develop the characteristics of puberty.)

Behavioural challenges linked to anxiety, rigidity in thinking and emotional control.

Short stature – with the availability of growth hormone treatment in New Zealand today, this feature is rarely seen as children have a chance of reaching their natural expected height (in addition to experiencing an improvement in body composition.)

Note: The characteristics above describe the PWS ‘phenotype’ (symptoms usually present which characterise PWS), but it is important to understand that PWS is a spectrum disorder with a range of associated symptoms found listed throughout this website. Individuals may experience less or more of these with each symptom varying in severity.

What causes the characteristics of PWS?

It is thought that most of the symptoms associated with PWS are likely to be caused by hypothalamic dysfunction. The hypothalamus is a small endocrine organ within the brain which links the endocrine and nervous systems via the pituitary gland. It is responsible for producing many of the body’s hormones and controls endocrine functions such as metabolism and growth. It also plays a role in governing functions such as temperature regulation, thirst, hunger, the sleep/wake cycle, mood, the expression of emotions and the feeling of pain, all of which can be affected in Prader-Willi Syndrome.

There is still much to learn about specific causes of the different characteristics of PWS and ongoing research is looking to further understand, alleviate, or even cure, some of these symptoms. The PWSA(NZ) supports the work of The Foundation for Prader-Willi Research and other organsisations who fund PWS research.

The genetics of Prader-Willi syndrome

There are 3 main ways in which PWS occurs. In each genetic subtype a segment of genes on the paternal chromosome 15 are prevented from working (15q11-13) because they are either deleted or unexpressed:

Deletion – genes on the paternal copy of chromosome 15 are deleted. This is the most common cause of PWS and occurs in approximately 70% of cases.

Uniparental Disomy (UPD) – two copies of the maternal chromosome 15 are received and the paternal chromosome 15 is missing. Occurs in approximately 30% of cases.

Imprinting defect – the paternal chromosome 15 is complete but the PWS segment of genes are inactive / do not work. Occurs in approximately 1-3% of cases.

The differences between these genetic subtypes are subtle and there is no feature that is exclusively found in one group. A fourth way in which PWS can occur is through a traumatic brain injury, although the person will not present with the physical characteristics of PWS.

The basic care and support needs of a person with PWS

Due to increased feelings of hunger, a preoccupation with food and the altered body composition (reduced muscle mass / increased fat mass) reducing energy expenditure, significant weight gain can rapidly occur. The altered body composition means that individuals with PWS need to eat considerably less for their age than their peers, so dietary intervention is usually required throughout their lifetime. For many individuals, this means close supervision with controlled access to food. Appropriate dietary management helps to prevent obesity and the occurrence of any life threatening situations caused by ‘binge eating’ episodes (quickly consuming large volumes of food.) Please check with primary carers before offering food to someone affected by PWS. Promoting exercise is also key to caring for someone with PWS because not only does it burn energy and help with weight management, but exercise can help strengthen muscles and an improved body composition reduces the amount of dietary restriction required. Other benefits of exercise are keeping bones strong, increasing cardiovascular health, improving mood and reducing anxiety. Unfortunately, individuals with PWS can be reluctant to exercise due to low muscle tone, fatigue or poor motor skills and therefore require much encouragement.

Young children with PWS benefit from a multi-disciplinary early intervention approach under the care of an endocrinologist and paediatrician; this may include therapists such as neurodevelopmental therapists, occupational therapists, physios and speech and language therapists. In New Zealand, most children with PWS attend mainstream primary school but benefit from specialist teacher or teacher aide support. Families, schools and carers may face some challenging behaviours, but planning and implementing consistent, positive behaviour management strategies can effectively improve behaviours. If needed, support for behaviour may be found through health professionals and behaviour support services such as ‘Explore’. Adults with PWS usually require a supported living arrangement, with one of the main obstacles to independent living often being the inability to control food intake.

The presentation and severity of PWS symptoms varies in individuals so the level of care and support required will also differ. It is also common for the levels of support needed to fluctuate throughout a person’s life as they experience the different phases of PWS and through periods of change or transition. It’s important to note that caring for someone with PWS impacts on family stress levels and families should be encouraged to look after their own health too.