Prader–Willi syndrome
A rare genetic disorder causing insatiable hunger and developmental challenges.
Prader–Willi syndrome (PWS) is a rare genetic disorder caused by a loss of function of specific genes on chromosome 15. It is characterized by a distinct set of symptoms that evolve from infancy through adulthood, including weak muscles, poor feeding, and slow development in babies, followed by constant hunger, obesity, mild to moderate intellectual impairment, and behavioral problems beginning in childhood. The syndrome is notable for being one of the first recognized human disorders related to genomic imprinting.
- prevalence
- 1 in 10,000 to 30,000 people worldwide
- total_affected
- More than 400,000 people live with PWS
- genetic_cause
- Loss of function of genes on chromosome 15 (region 15q11-13)
- most_common_mechanism
- Deletion of part of the father's chromosome 15 (74% of cases)
- inheritance_pattern
- Not generally inherited; risk to sibling <1% for deletion or uniparental disomy
- associated_disorder
- Angelman syndrome (similar mechanism, but defective maternal chromosome)
Lore & Background
Prader–Willi syndrome results from the loss of function of specific genes on chromosome 15, most often due to a deletion of part of the father's chromosome 15 (74% of cases). In another 25% of cases, the affected person inherits two copies of the maternal chromosome 15 and lacks the paternal copy; because maternal copies are silenced through imprinting, no working copies of certain genes remain. The genetic changes typically occur during the formation of the egg, sperm, or in early development, and no risk factors are known. The syndrome is not generally inherited, and those who have one child with PWS have less than a 1% chance of the next child being affected.
Reader's Guide
Prader–Willi syndrome has no cure, but treatment can improve outcomes, especially if carried out early. In newborns, feeding difficulties may be supported with feeding tubes. Strict food supervision is typically required starting around age three, combined with an exercise program. Growth hormone therapy improves outcomes, and counseling and medications may help with some behavioral problems. Group homes are often necessary in adulthood. The syndrome is the most common genetic cause of morbid obesity in children. Psychiatric and behavioral problems are the most common cause of hospitalization. The deletion of the 29 copies of the C/D box snoRNA SNORD116 (HBII-85) is considered the primary cause of PWS. With early diagnosis and early treatment, the prognosis is beginning to change.
Did You Know?
- About 74% of PWS cases occur when part of the father's chromosome 15 is deleted.
- People with PWS have high ghrelin levels, which are thought to contribute directly to increased appetite and hyperphagia.
- PWS is the most common genetic cause of morbid obesity in children.
- A similar genetic mechanism occurs in Angelman syndrome, but with the defective chromosome 15 from the mother.
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