Prader-Willi Syndrome (PWS)

Prader-Willi syndrome (PWS) is a rare, genetic neurobehavioral disorder that affects multiple organ systems: metabolic, endocrine, neurological, and musculoskeletal. PWS is characterized by hypotonia and feeding difficulties in infancy and by global developmental delays, cognitive impairment, behavioral problems, and hyperphagia leading to obesity from early childhood through young adulthood. PWS is recognized as the most common genetic cause of life-threatening obesity.1

Incidence and Prevalence of PWS

Most studies estimate the incidence of PWS to be 1 in every 10,000 to 30,000 live births.2-4 The global prevalence of PWS ranges from 1 to 9 per 100,000 individuals.5 PWS affects between 350,000 and 400,000 individuals around the world.1,2

Race/Ethnicity Factors of PWS

PWS affects people of all races and ethnicities.1-4 

The Global PWS Registry includes individuals with PWS living in the United States in addition to individuals from 38 other countries or territories across the world. Within the Registry, 935 individuals with PWS reported their race and 767 reported their ethnicity.4 

Most of the 935 Global PWS Registry participants reported their race as Caucasian (85.1%). Less frequently, they listed their race as multi-ethnic (7.1%), Asian (3.0%), Black or African American (1.5%), American Indian or Alaskan Native (0.4%), Native Hawaiian or Pacific Islander (0.3%), or other (1.8%). The remaining 0.7% either did not know (0.1%) or preferred not to answer (0.6%).4

Of the 767 individuals who reported their ethnicity, 82% stated it to be non-Hispanic or Latino, 9.5% Hispanic or Latino, 2.5% Ashkenazi Jewish, 3.9% unknown, and 2.1% preferred not to answer.4 

Read more about PWS etiology

Geographical Factors of PWS

PWS occurs in all geographic regions of the world.2 Approximately 10,000 to 20,000 individuals with PWS live in the United States.1,4

Age Factors of PWS

Formal diagnostic criteria suggest that PWS is usually diagnosed before the age of 3 to 3.9 years on the basis of severe hypotonia and a history of feeding difficulties during infancy.1,6 At about 3 years of age, other symptoms, such as hyperphagia, learning disabilities, behavioral problems (particularly when food is involved), and the onset of obesity, become more noticeable.6 

Because PWS is a genetic disorder inherited at conception and fetal DNA circulates in the mother’s blood after 9 to 10 weeks of gestation, noninvasive methylation testing can be used prenatally to detect fetal DNA methylation and diagnose PWS.7 In developing countries, PWS is diagnosed at an average age of 8.6 weeks. Globally, a PWS diagnosis is confirmed at an average age of 3.9 years.1 

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The Global PWS Registry subdivides participants according to age at enrollment: 13% younger than 2 years of age, 18% between 2 and 5 years, 20% between 6 and 10 years, 17% between 11 and 15 years, 12% between 16 and 20 years, 12% between 21 and 30 years, and 8% older than 30 years.4 

Sex Factors of PWS

Prader-Willi syndrome affects females and males equally.1-4 The gender distributions of affected individuals were relatively equal according to the Global PWS Registry: 51% male and 49% female.4

Impact of Disease Subtype on PWS

PWS is divided into 3 main molecular genetic subtypes: paternal deletions on chromosome 15, maternal uniparental disomy (UPD), and imprinting center defects.4,8 A definitive molecular genetic test, the DNA methylation test, accurately confirms up to 99% of all cases of PWS.1,5

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Approximately 60% to 70% of cases of PWS are caused by paternal microdeletions on chromosome 15q11-q13, which are then subdivided into type I (7 megabases), type II (5 megabases), and atypical deletions.4,8

Between 30% and 40% of PWS cases are due to maternal UPD following trisomic rescue.4,8

A small minority of cases, between 1% and 3%, are due to imprinting center defects.4,8

Very rarely (~0.1% of cases), PWS may be caused by translocations of chromosome 15 and other chromosomes. The PWS region of chromosome 15 is complex and includes embedded short noncoding RNAs, long noncoding RNAs, and protein-coding genes.8-10

Read more about PWS types


  1. Fermin Gutierrez MA, Mendez MD. Prader-Willi syndrome. In: StatPearls [Internet]. Updated January 31, 2023. Accessed July 13, 2023. 
  2. Prader-Willi syndrome. NORD. Updated July 12, 2023. Accessed July 13, 2023.
  3. What is Prader-Willi syndrome? Foundation for Prader-Willi Research. Accessed July 13, 2023.
  4. Bohonowych J, Miller J, McCandless SE, Strong TV. The Global Prader-Willi Syndrome Registry: development, launch, and early demographics. Genes (Basel). 2019;10(9):713. doi:10.3390/genes10090713
  5. Prader-Willi syndrome. Orphanet. Accessed July 13, 2023.
  6. How do healthcare providers diagnose Prader-Willi syndrome (PWS)? NIH – Eunice Kennedy Shriver National Institute of Child Health and Human Development. Accessed July 13, 2023.
  7. How is Prader-Willi syndrome diagnosed? PWSA Victoria. Accessed July 13, 2023.
  8. Zhang L, Liu X, Zhao Y, et al. Genetic subtypes and phenotypic characteristics of 110 patients with Prader-Willi syndrome. Ital J Pediatr. 2022;48(1):121. doi:10.1186/s13052-022-01319-1
  9. Genetics of Prader-Willi syndrome and Prader-Will-Like syndrome. Ann Pediatr Endocrinol Metab. 2016;21(3):126-135. doi:10.6065/apem.2016.21.3.126
  10. Cheon CK. Prader-Willi syndrome. MedlinePlus. Accessed July 13, 2023.

Reviewed by Debjyoti Talukdar, MD, on 7/17/2023.