A brief guide to Prader-Willie Syndrome

Who has Prader-Willi syndrome (PWS)?

Anyone can be born with Prader-Willi syndrome (PWS). Some individuals may also acquire PWS as a result of trauma to the brain.

What is Prader-Willi syndrome?

PWS is a complex genetic disorder affecting appetite, growth, metabolism, cognitive function and behavior. It is typically characterized by low muscle tone, short stature (when not treated with growth hormone), incomplete sexual development, cognitive disabilities, behavioral problems, and the hallmark characteristics – chronic feelings of insatiable hunger and a slowed metabolism that can lead to excessive eating and life-threatening obesity. Those who have PWS need intervention and strict external controls, sometimes including padlocking access to food, to maintain normal weight and to help save their lives.

How many people have Prader-Willi syndrome?

It is estimated that one in 12,000 to 15,000 people has PWS. Although considered a “rare” disorder, PWS is one of the most common conditions seen in genetic clinics and is the most common genetic cause of obesity that has been identified to date.

Where is Prader-Willi syndrome found?

PWS is found in people of both sexes and in all races worldwide.

Why does Prader-Willi syndrome occur?

Most cases of PWS are attributed to a spontaneous genetic error that occurs at or near the time of conception for unknown reasons. In a very small percentage of cases (2 percent or less), a genetic mutation that does not affect the parent is passed on to the child, and in these families, more than one child may be affected. A PWS-like disorder can also be acquired after birth if the hypothalamus portion of the brain becomes damaged through injury or surgery.

What is the cause of Prader-Willi syndrome?

Basically, the occurrence of PWS is due to lack of several genes on one of an individual’s two chromosome 15’s – the one normally contributed by the father. In the majority of cases, there is a deletion – the critical genes are somehow lost from the chromosome. In some of the remaining cases, the entire chromosome from the father is missing and there are instead two chromosome 15’s from the mother (uniparental disomy). The critical paternal genes lacking in people with PWS have a role in the regulation of appetite. This is an area of active research in a number of laboratories around the world, since understanding this defect may be very helpful not only to those with PWS, but to understanding obesity in otherwise normal people.

People with PWS have a flaw in the hypothalamus part of their brain, which normally registers feelings of hunger and satiety. While the problem is not yet fully understood, it is apparent that people with this flaw never feel full; they have a continuous urge to eat that they cannot learn to control. To compound this problem, people with PWS need less food than their peers without the syndrome because their bodies have less muscle and tend to burn fewer calories.

Who do I contact for additional information?







Contact the Prader-Willi Syndrome Association –
PWSA UK, Suite 4.4, Litchurch Plaza,
Litchurch Lane,
Derby DE24 8AA


t: 01332 365676
f: 01332 360401