Your browser does not support javascript:   Search for gard hereSearch for news-and-events here.


Genetic and Rare Diseases Information Center (GARD)

Print friendly version

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
See Disclaimer regarding information on this site. Some links on this page may take you to organizations outside of the National Institutes of Health.

Tests & Diagnosis

Newline Maker

How might Prader-Willi syndrome be diagnosed?

Signs of Prader-Willi syndrome may be seen at birth. Newborns with the condition are often small and very floppy. Male infants may have undescended testicles. As the child grows older, laboratory tests may show signs related to morbid obesity, such as abnormal glucose tolerance, above normal level of insulin in the blood, excessive carbon dioxide levels, and failure to respond to luteinizing hormone releasing factor.[1]

Individuals are usually diagnosed through molecular testing, which consists of DNA-based methylation testing to detect abnormal parent-specific imprinting within the Prader-Willi critical region (PWCR) on chromosome 15. This testing determines whether the region is maternally inherited only (the paternally contributed region is absent) and detects more than 99% of affected individuals. Methylation-specific testing is important to confirm the diagnosis of PWS, especially in those who have atypical findings or are too young to show significant features to make a clinical diagnosis.[2] This testing can be coordinated by a genetics professional at a genetics clinic.
Last updated: 4/1/2011

  1. O'Reilly D. Prader-Willi syndrome. MedlinePlus. November 2, 2009; Accessed 3/24/2011.
  2. Cassidy SB, Schwartz S. Prader-Willi Syndrome. GeneReviews. September 2009; Accessed 3/24/2011.