British Columbia
Prader-Willi Syndrome Association
BCPWSA is here for you.
We are a non-profit charity that provides an understanding and awareness of Prader-Willi Syndrome by supporting those who have the syndrome, their families, and all those who come in contact with PWS.
Learn more about how you can receive help and support.
Become a member.
If you or a family member is affected by PWS, we encourage you to become a member of our association.
What is Prader-Willi Syndrome?
What is PWS?
Prader-Willi Syndrome (PWS) is a complex genetic disorder that typically causes low muscle tone, short stature, incomplete sexual development, cognitive disability, challenging behaviours and a chronic feeling of hunger that can lead to excessive eating and life-threatening obesity.
Click this button to learn more about Prader-Willi Syndrome.
How common is PWS?
It is estimated that 1 in 15,000 people are born with PWS. PWS affects males and females with equal frequencies and affects all races and ethnicities. The occurrence of PWS is caused by a lack of genetic material in a particular region of chromosome 15 (15q11-q13). Individuals typically inherit one copy of chromosome 15 from their mother and one copy of chromosome 15 from their father. Normally, the genes in the PWS region are only active in the chromosome copy from the father. PWS can occur in three different ways, due to this genetic defect causing the inactivity of the paternal chromosome 15:
PWS dy deletion
In the majority of cases (70%), there is a small deletion – the critical genes are somehow lost or deleted from the chromosome normally inherited from the father.
PWS by UPD
In most of the remaining cases (just under 30%), the entire chromosome from the father is missing and there are instead two chromosome 15s inherited from the mother. This is termed uniparental disomy. (UPD15)
PWS by Imprinting Defect
In a very small amount of cases (1-3%), a small genetic mutation in the PWS region causes the paternal chromosome 15 genetic material to be inactive (even though it is actually there).
How is PWS DIAGNOSED?
Prader-willi syndrome is diagnosed with a blood test that looks for the genetic abnormalities that are specific to PWS. This is called a methylation analysis. It can detect all types of PWS and is the preferred test for diagnosis. A FISH test (fluorescence in-situ hybridization) can identify PWS by deletion, but it does not diagnose other types of PWS. If a methylation test is done first, additional testing may be needed to determine whether PWS is caused by a paternal deletion, UPD, or an imprinting mutation. In the case where an imprinting mutation is suspected, blood testing may also be done from the parents.
Does the overeating associated with PWS start at birth?
No. In fact, newborns with PWS often cannot get enough nourishment because low muscle tone impairs their ability to suckle. Many require special feeding techniques or tube feeding for several months after birth, until muscle control improves. Sometime, in the following years, usually before school age, children with PWS develop an intense interest in food and can quickly gain excess weight if calories are not monitored.
Research is always happening, but there are several stages to consider when caring for a person with PWS. In the past, PWS was only described as a 2 stage syndrome – failure to thrive (poor feeding and slow growth) followed by hyperphagia (increased appetite). After observing that the changes in appetite and weight gain which occur in PWS are more gradual and complex than traditionally described, a research team investigated and presented an updated clinical description of the nutritional phases of PWS. Their research was published in 2011 outlining 5 major phases, including some sub-phases.
Phases of PWS
Phase Ages Characteristics
0 prenatal-birth Decreased fetal movements and lower birth weight than siblings
1a 0-9 months Hypotonia with difficulty feeding and decreased appetite
1b 9-25 months Improved feeding and appetite; growing appropriately
2a 2.1-4.5 years Weight increasing without appetite increase or excess calories
2b 4.5–8 years Increased appetite and interest in food, but can feel full
3 8 years–adult Hyperphagic; rarely feels full
4 adulthood Appetite is no longer insatiable (only very few adults)
*A more detailed version can be found below.
PWS is a spectrum disorder and symptoms vary in severity and occurrence among individuals.
Phases of Prader-Willi Syndrome - detailed
Phase 0
Decreased fetal movements and lower birth weight
Full-term birth weight and BMI are about 15–20% less than the siblings
Typically normal gestational age
85% have decreased fetal movements
Phase 1a
Hypotonia with difficulty feeding (0–9 months)
Weak, uncoordinated suck. Usually cannot breastfeed
Needs assistance with feeding either through feeding tubes (nasal/oral gastric tube or gastrostomy tube) or orally with special, widened nipples. Many would die without assisted feeding
Oral feeds are very slow
Severely decreased appetite. Shows little or no evidence of being hungry
Does not cry for food or get excited at feeding time
If feeding just occurred when baby “acted hungry” then would have severe “failure-to-thrive”
Weak cry
Phase 1b
No difficulty feeding and growing appropriately on growth curve (9–25 months)
No longer needs assisted feeding
Growing steadily along growth curve with normal feeding
Normal appetite
Phase 2a
Weight increasing without an increase in appetite or excessive calories (2.1–4.5 years)
Infant starts crossing growth curve centile lines
No increase in appetite
Appetite appropriate for age
Will become obese if given the recommended daily allowance (RDA) for calories or if eating a “typical” toddler diet of 70% carbohydrates
Typically needs to be restricted to 60–80% of RDA to prevent obesity
Phase 2b
Weight increasing with an increase in appetite (4.5–8 years)
Increased interest in food. Frequently asking “food related” questions
Preoccupied with food. Very concerned about the next meal/snack (e.g., “Did you remember to pack my lunch?”)
Increased appetite
Will eat more food than a typical child if allowed
Will eat food within their line of sight if unattended
Will become obese if allowed to eat what they want
Can be fairly easily redirected about food
Can feel full
Will stop eating voluntarily
Phase 3
Hyperphagic, rarely feels full (8 years adulthood)
Constantly thinking about food
While eating one meal they are already thinking about the next meal
Will awaken from sleep early thinking about food
Will continue eating if portion size is not limited
Rarely (truly) feels full
Will steal food or money to pay for food
Can eat food from garbage and other unsavory/inedible sources (e.g., dog food, frozen food, crayons, etc.)
Typically are not truthful about what they have eaten (i.e. amount and types of food)
Will gain considerable amount of weight over a short period of time if not supervised (e.g., some individuals are known to have gained up to 20 pounds in one weekend)
Food typically needs to be locked up. Frequently the child will ask the parent to lock the food if the parent has forgotten
Will break into neighbors’ houses for food
Temper tantrums and “meltdowns” frequently related to food
Needs to be placed on a diet that is approximately 50–70% of the RDA to maintain a healthy weight
Phase 4
Appetite is no longer insatiable (adulthood)
Appetite may still be increased or may be normal or less than normal
Previously in phase 3, but now a noticeable improvement in their appetite control
Can feel full
Appetite can fluctuate in this phase, but the key component is noticeable improvement in control of appetite compared to when they were younger
Not as preoccupied with food
Absence of major temper tantrums and “meltdowns” related to food
Onset in adulthood. Could be as early as 20s or as late as 40–50s
Most adults have not gone into this phase and maybe some (most?) never will
What causes the appetite & obesity STRUGGLES in PWS?
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 truly 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. Unfortunately, no appetite suppressant has worked consistently for people with PWS. Most require a low caloric diet all their lives and must have their environments designed so that they have limited access to food.
What kinds of behavior STRUGGLES do people with PWS have?
In addition to their involuntary focus on food, people with PWS tend to have obsessive/compulsive behaviours that are not related to food, such a repetitive thoughts and verbalizations, collecting and hoarding possessions, picking at skin irritations, and a strong need for routine and predictability. Frustration or changes in plans can easily set off a loss of emotional control in someone with PWS, ranging from tears to temper tantrums to physical aggression.
