Last Reviewed June 2, 2009
Symptoms & Characteristics
Prader-Willi (PWS) syndrome is genetic condition that affects the development and growth of various parts of the body. Some of the more common characteristics may include:
- low muscle tone (hypotonia) at birth
- developmental delay or mental retardation
- excessive eating and the gradual development of obesity (if untreated)
- small genitalia (in males and females)
- infertility (in most people)
- light colored hair and fair skin
- characteristic facial features
- characteristic behaviors (tantrums, stubbornness, obsessive-compulsive, etc.)
Treatment
There is no cure for Prader-Willi syndrome. However, early diagnosis, routine surveillance and treatment can help to manage some of the symptoms and sometimes prevent related problems.
How Common Is It?
About 1 in 10,000 to 1 in 25, 000 people are affected with Prader-Willi syndrome.
Genetics & Inheritance
Prader-Willi Syndrome is caused by the loss of the paternally contributed PWS critical region including several active genes on chromosome 15 at the location q11-q13. The exact genetic cause of PWS is currently under investigation.
People normally inherit one copy of the PWS critical region from each parent. Some genes in this region are active only when inherited from father (paternal copies). This parent-specific gene activation is called genomic imprinting. If the paternal copy of the chromosome region 15q11-q13 is lost, a person will have no active copies of some genes and will have the symptoms of PWS.
Loss of the paternal copy of 15q11-q13 can occur by one of several mechanisms. These mechanisms may include:
- Deletion of 15q11-q13 (70-75% of cases).
- Maternal uniparental disomy (UPD), which means that two normal copies of the entire chromosome 15 or the 15q11-q13 region are present, but they both are inherited from the same parent, mom (25-30% of cases).
- Imprinting errors caused by a DNA methylation abnormality, which leads to no active paternal copy.
The deletion of the OCA2 gene in this same region is associated with the light-colored hair and fair skin in people with PWS.
Most people who are affected with PWS do not have a family history, and they are the first one in their family to be affected. The recurrence risk for PWS varies and depends on the specific mechanism by which the paternal copy was lost.
There are other genetic conditions, like Rett syndrome, that have features that overlap with Prader-Willi syndrome. A genetic consultation with a trained genetic professional is important for a complete evaluation, accurate diagnosis, as well as discussion of the benefits and limitations of testing and recurrence risk.
Genetic Testing
Clinical genetic testing for Prader-Willi syndrome may be available through an in person
genetic consultation for people who are considered at risk. Use our
find a genetic professional directory to locate a trained
genetic professional in your area.
Support & More Information
More information can be found at:
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Alternative Names
- Prader-Labhart-Willi syndrome
- PWS