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Prader-Willi syndrome

Other Names for this Disease
  • Obesity, muscular hypotonia, mental retardation, short stature, hypogonadotropic hypogonadism, and small hands and feet
  • Prader Labhart Willi syndrome
  • PWS
  • Willi-Prader syndrome
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What causes Prader-Willi syndrome?

Prader-Willi syndrome is caused by the loss of active genes in a specific region of chromosome 15.[1][2][3] People normally inherit one copy of this chromosome from each parent. Some genes are only active on the copy that is inherited from a person's father (the paternal copy). This parent-specific gene activation is called genomic imprinting.

About 70 percent of cases of Prader-Willi syndrome occur when the region of the paternal chromosome 15 containing these genes is missing.[1]  In 25 percent of cases, a person with Prader-Willi syndrome has two copies of chromosome 15 inherited from his or her mother (maternal copies) instead of one copy from each parent, which is called maternal uniparental disomy. Rarely, Prader-Willi syndrome is caused by a chromosomal rearrangement called a translocation, or by a mutation or other defect that abnormally inactivates genes on the paternal chromosome 15. Each of these genetic changes results in a loss of gene function in a critical region of chromosome 15.[1]

Researchers are working to identify genes on chromosome 15 that are responsible for the characteristic features of Prader-Willi syndrome. Researchers have determined, however, that a deletion of the OCA2 gene on chromosome 15 is associated with unusually fair skin and light-colored hair in some affected individuals. The protein produced from this gene helps determine the coloring (pigmentation) of the skin, hair, and eyes.[1]
Last updated: 4/1/2011

  1. Prader-Willi syndrome. Genetics Home Reference (GHR). July 2009; Accessed 3/24/2011.
  2. O'Reilly D. Prader-Willi syndrome. MedlinePlus. November 2, 2009; Accessed 3/24/2011.
  3. Prader-Willi Syndrome. National Institute of Child Health and Human Development (NICHD). March 24, 2010; Accessed 3/24/2011.