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Prader Willi Syndrome

The frequency of Prader Willi syndrome is 1 in 10,000 to 25,000 births.

This is a chromosomal abnormality where a micro deletion occurred at chromosome 15 (15q11-q13). The cause of this is a defective paternal gene, which wipes out the health corresponding maternal copy. The end result is an individual with mental retardation, obesity, a short stature overeating constantly. A mirror image of chromosome 15 (15q11-q13) micro deletion where the defective gene comes from the mother is called Angelman syndrome (see link under “Related Topics” below).

Signs and Symptoms

A baby with Prader Willi syndrome often presents as a breech delivery. In the newborn nursery the baby has no muscle strength (hypotonia), presents with feeding problems and has a low body temperature. The feet and hands are small in relationship to the rest of the body. The patient with Prader Willi syndrome appears to have no feeling of satiation and this is the reason why over the course of years obesity develops: fat boy eating. The forehead is narrow, the face is long and the eyes are in the shape of almonds.

As the child grows up the hypotonia problem disappears, but small stature, hypogonadism and obesity remain. Patients have a mild to moderate mental retardation and they seem to be sleep longer than normal (hypersomnia).


As this is a genetic syndrome, there is no treatment for the condition. These individuals will need to live in a supportive environment and often end up in a specialized home that is equipped to deal with these patients.

 Prader Willi Syndrome (Often Comes As Breech Delivery)

Prader Willi Syndrome (Often Comes As Breech Delivery)



1. Behrman: Nelson Textbook of Pediatrics, 17th ed., Copyright © 2004 Saunders, An Imprint of Elsevier: Chapter 70 – Chromosomal Clinical Abnormalities


Last modified: April 18, 2021

This outline is only a teaching aid to patients and should stimulate you to ask the right questions when seeing your doctor. However, the responsibility of treatment stays in the hands of your doctor and you.