Prader- Willi Syndrome

Summary and Description

What is it?

A complex, mulit-system genetic disorder affecting appetite, growth, metabolism, cognitive function and behavior.


Patients exhibit the following KEY characteristics:

  • Infantile hypotonia (low tone)
  • Developmental delays and intellectual disability
  • Behavioral disorders
  • Characteristic facial appearance
  • Obesity (due to insatiable hunger and slowed metabolism)
  • Hypogonadism
  • Short stature


**People with Prader-Willi Syndrome do not recognize the feeling of being full after eating


(Lewis, Freebarirn, Heeger, & Cassidy, 2002)


image sources: http://geneticsperiod4.wikispaces.com/Prader-Willi+Syndrome (above)

http://www.aafp.org/afp/2005/0901/p827.html (below)

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4 Distinct Nutritional Phases

Not all adults reach stage 4- in fact, most do not


image source: http://www.nature.com/gim/journal/v14/n1/fig_tab/gim0b013e31822bead0t1.html (below)

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How does it happen?

It is the result of the loss of function due to imprinted genes on chromosome 15- it is the first known human genomic imprinting disorder.


Can occur one of three possible ways:


  1. The paternally contributed associated region of chromosome 15 is deleted (70% of cases)
  2. Two copies of chromosome 15 are inherited from the mother, and no copy inherited from the father aka. Maternal UPD (25% of cases)
  3. Imprinting deficits: a structural abnormality of chromosome 15 or an error in the process of activating paternal genes (5% of cases)


(Lewis et al, 2002)

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It is estimated that 1 in every 12,000- 15,000 people are living with Prader- Willi Syndrome

  • It effects men and women equally
  • It is seen worldwide among all races
  • It is the most common identified genetic cause of obesity


http://www.pwsausa.org/about-pws/basic-facts-about-pws