Prader-Willi Syndrome

What is Prader-Willi Syndrome?

Prader-Willi Syndrome (PWS), which was named for the two doctors who first identified it, is a complex genetic disorder that causes short stature, weak muscle tone, incomplete sexual development, and obesity, as well as cognitive disabilities and behavior problems. About one in 15,000 babies inherits the genetic abnormality that causes Prader-Willi Syndrome.

DNA testing

If a doctor suspects that a child has PWS, She will order genetic testing to confirm the diagnosis. The current test for PWS is called DNA methylation analysis and is more accurate than the tests that were used in the past. If you suspect that your child has PWS, but previous tests were negative or inconclusive, the Prader-Willi Syndrome Association advocates retesting, using the new, more accurate technology.

Physical signs

There are many physical signs associated with PWS. These include distinctive facial features, such as almond-shaped eyes and small, downturned mouths, small hands and feet, and hair and skin that is unusually light compared with other members of the family.

Babies born with PWS often have feeding problems and poor weight gain in their first year of life, but gain weight rapidly after their first birthday. A defect in the hypothalamus, the region of the brain that regulates hunger and appetite, makes people with PWS feel constantly hungry no matter how much they eat. In addition, decreased muscle mass slows their metabolism so their bodies utilize fewer calories. (Adults with PWS need only 1000-1200 calories a day or they will gain weight.) Without intervention, many children with PWS will be obese by the time they are six.

Children with PWS grow more slowly than other children and often have delayed or incomplete sexual maturity. Boys may have undescended testes and a small penis, while girls may not get their periods.

Cognitive and behavioral problems

There are numerous cognitive and behavioral problems linked to PWS as well. Children with PWS may experience a general developmental delay of one to two years, mild to moderate mental retardation, or learning disabilities. IQ ranges from 40 to 105 with 70 being typical. They may also have problems with speech articulation due to weak mouth muscles. Children with PWS also tend to be clumsy because of weak muscle tone.

A range of behavioral problems is also associated with PWS, including temper tantrums and violent outbursts, depression, and obsessive-compulsive disorder.

But medical intervention, including treatment with growth hormone, may ease many of the problems associated with PWS. In some cases, growth hormone can help children with PWS grow taller, increase their muscle mass, and develop normal sexual characteristics. In addition, growth hormone helps increase strength and coordination. Since regular exercise is very important to keep weight gain down, this aspect of growth hormone treatment is particularly important. Serotonin reuptake inhibitors help to reduce compulsive behaviors, though they’ve been associated with an increase in suicidal thoughts and behavior. You should always discuss your treatment options thoroughly with your doctor.

A research overview at Brown University found that treatment with growth hormone helped reduce behavior problems as well as physical symptoms. Researchers speculate that the improved body image which comes with growth hormone treatment helped combat the tendency toward depression. In addition, PWS patients taking growth hormone also had more physical energy and exercised more, which also had a beneficial effect on their mood.

For more information or support, contact the Prader-Willi Syndrome Association at or by calling the toll-free helpline, (800) 926-4797.


FAQ from Prader-Willi Syndrome Association (USA):

Prader-Willi Syndrome Association website: Fact sheet form PWSA:

Wattendorf DJ et al. Prader-Willi Syndrome. American Family Physician. Volume 72, Number 5. September 1, 2005.

Mayo Clinic. Selective serotonin reuptake inhibitors. December 2006.

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