Merck Manual

Please confirm that you are not located inside the Russian Federation


Prader-Willi Syndrome


Nina N. Powell-Hamilton

, MD, Sidney Kimmel Medical College at Thomas Jefferson University

Last full review/revision Jul 2020| Content last modified Jul 2020
Click here for the Professional Version
NOTE: This is the Consumer Version. DOCTORS: Click here for the Professional Version
Click here for the Professional Version

Prader-Willi syndrome is a chromosomal deletion syndrome in which part of chromosome 15 is missing.

About 70% of people who have Prader-Willi syndrome are missing part of chromosome 15. About 30% of people who have this syndrome have problems with the function of chromosome 15.


Many symptoms of Prader-Willi syndrome vary according to the child's age. Newborns with the defect feel limp, feed poorly, and gain weight slowly. Eventually these symptoms resolve. Then, between the ages of 1 and 6, appetite increases, often becoming insatiable. Children rapidly gain weight. The hands and feet remain small, and children remain short. Abnormalities of the face include almond-shaped eyes and a mouth with thin upper lips and down-turned corners. Children have bone disorders (such as scoliosis and kyphosis). Obsessive-compulsive behaviors are common. Hormonal problems are common, and the function of the reproductive organs is abnormally decreased, which limits growth and sexual development. Boys have undescended testes (cryptorchidism) and an underdeveloped penis and scrotum. Intellectual disability is common. Weight gain continues into adulthood and is excessive, which can lead to other health problems, such as obesity. Obesity can be severe enough to justify gastric bypass surgery.


  • Chromosomal testing

The diagnosis of Prader-Willi syndrome may be suspected before birth or by the child's physical characteristics after birth. The diagnosis can be confirmed by chromosomal testing.


  • Sometimes growth hormone

Ongoing research is being done to find treatments that help improve the prognosis for children and adults who have Prader-Willi syndrome. Many research studies show that human growth hormone is beneficial.

NOTE: This is the Consumer Version. DOCTORS: Click here for the Professional Version
Click here for the Professional Version
Others also read

Also of Interest


View All
Overview of Attention-Deficit/Hyperactivity Disorder...
Overview of Attention-Deficit/Hyperactivity Disorder...
3D Models
View All
The Common Cold
3D Model
The Common Cold