What's Prader-Willi syndrome?
Prader-Willi syndrome (PWS) is a genetic disorder caused by the loss of genes that are normally active only on the chromosome 15 inherited from the father (the 15q11-q13 region). It produces low muscle tone in infancy, then an insatiable appetite (hyperphagia) and obesity, short stature, incomplete sexual development, and learning difficulties.
| Also indexed as | OMIM:176270, MONDO:0008300 |
|---|---|
| Features mapped | 20 |
| Treatments mapped | 2 |
| Published sources | 16 |
| Last reviewed | 2026-08-04 |
Signs and symptoms
Small hand
In Prader-Willi syndrome, small hands and feet are often noticed in childhood, along with short stature and slower thinking and learning.
Impaired pain sensation
In Prader-Willi syndrome, pain may be felt less than expected (a high pain threshold), which can mean injuries or illness are noticed late; this is thought to reflect dysfunction of the hypothalamus rather than a problem with the affected body part itself.
Global developmental delay
Developmental and cognitive delay is one of the defining features of PWS, affecting motor milestones, speech, and learning across childhood.
Intellectual disability
Most people with Prader-Willi syndrome have some degree of intellectual disability, usually mild to moderate, along with specific learning difficulties. Support tailored to these needs makes a meaningful difference across school and daily life.
Polyphagia
In Prader-Willi syndrome, an insatiable appetite (never feeling full) drives excessive eating, and this is the main factor behind the severe obesity that can develop.
Self-injurious behavior
Repetitive skin picking (excoriation) is a characteristic self-injurious behavior in Prader-Willi syndrome, part of the syndrome's distinctive behavioral profile alongside compulsive symptoms and disruptive behavior. It can cause open sores and is one of the features clinicians watch for.
Sleep apnea
Sleep apnea (pauses in breathing during sleep) is among the findings seen in people with Prader-Willi syndrome, reported in a sizable share of patients.
Excessive daytime somnolence
Excessive daytime sleepiness (hypersomnia) is common in Prader-Willi syndrome. It is thought to stem from dysfunction of the hypothalamus, the brain region that also drives several of the syndrome's hormone and appetite features, and it is separate from sleep loss caused by obstructive sleep apnea.
Failure to thrive in infancy
Prader-Willi syndrome has two very different phases. In infancy, babies are floppy and feed poorly, often struggling to gain weight and needing feeding support. Only later in early childhood does the relentless hunger and weight gain begin.
Obesity
In Prader-Willi syndrome, severe obesity is driven by an insatiable appetite and is the main factor affecting long-term health.
Short stature
In Prader-Willi syndrome, short stature is often noticed in childhood, along with small hands and feet and slower thinking and learning.
Decreased response to growth hormone stimulation test
Many people with Prader-Willi syndrome make too little growth hormone, and on a growth-hormone stimulation test the peak response is low, which is one of the ways growth hormone deficiency is identified in the condition.
Hypogonadotropic hypogonadism
In Prader-Willi syndrome, the same problem in the hypothalamus (a control center deep in the brain) that affects appetite is also thought to cause hypogonadism, meaning the sex glands do not get the hormonal signals they need to develop and work normally.
Temperature instability
People with Prader-Willi syndrome can have trouble regulating body temperature (temperature instability), which is thought to stem from dysfunction of the hypothalamus, the brain region that controls many of the syndrome's features.
External genital hypoplasia
In Prader-Willi syndrome, the reproductive hormone system is underactive (hypogonadism), which commonly leads to underdeveloped external genitals (genital hypoplasia) and incomplete pubertal development.
Feeding difficulties in infancy
In early infancy, Prader-Willi syndrome typically causes severe low muscle tone with weak sucking and feeding difficulties, so babies often struggle to feed and may need extra support to take in enough nutrition.
Poor suck
In Prader-Willi syndrome, poor sucking is one of the main features of the newborn period, often together with low muscle tone, a weak cry, and feeding difficulties.
Neonatal hypotonia
In Prader-Willi syndrome, low muscle tone (hypotonia, meaning floppy, weak muscles) is one of the main features of the newborn period, often along with a weak cry, poor sucking, and feeding difficulties.
Generalized hypotonia
In Prader-Willi syndrome, the body usually starts out with very low muscle tone (severe hypotonia, meaning floppy, weak muscles) in early infancy, often with poor sucking and feeding difficulties. This is later followed by excessive eating and a gradual build-up of severe obesity in later infancy or early childhood.
Scoliosis
Curvature of the spine (scoliosis) is very common in Prader-Willi syndrome, eventually affecting most people by the time the skeleton matures. Low muscle tone and the way the spine grows both contribute, so the spine is monitored regularly throughout childhood.
How it is diagnosed
Prader-Willi syndrome
Diagnosed using: DNA methylation analysis (15q11-q13).
“Methylation‑specific multiplex ligation-dependent probe amplification and single nucleotide polymorphism microarrays were used to diagnose deletion and uniparental disomy (UPD).”
Treatment and management
What the research describes, not a recommendation. Treatment decisions belong with your clinician.
This covers treatments that appear in the published research mapped here. Investigational and experimental therapies are not included, so their absence is a boundary of this map, not a sign they do not exist.
Diazoxide choline extended-release
Diazoxide choline extended-release (sold as Vykat XR) is a once-daily medicine approved for treating hyperphagia (the relentless hunger and food-seeking) in people aged 4 years and older with genetically confirmed Prader-Willi syndrome.
Used to help with: Prader-Willi syndrome.
“Food and Drug Administration (FDA) approved Vykat XR (diazoxide choline-extended release tablets) for the treatment of hyperphagia in individuals aged 4 years and older with Prader-Willi Syndrome (PWS).”
Recombinant human growth hormone
Growth hormone therapy can have several benefits in Prader-Willi syndrome, including effects on growth and body composition (the balance of muscle and fat) and on motor and mental development.
Used to help with: Prader-Willi syndrome.
“All participants (100%) had a history of growth hormone treatment; 62.5% exhibited the deletion subtype.”
What changes how it shows up
Carrying the genetic change is not the whole story. The factors below are described in the research mapped here as changing whether, or how strongly, the condition appears. They modulate how the genotype is expressed; they do not, on their own, cause or cure it.
15q11-q13 paternal deletion / maternal UPD
Prader-Willi syndrome happens when the paternally active genes in the 15q11-q13 region are missing or silenced. In about 70% of cases this is from a deletion of that region on the father's chromosome 15, and in about 28% it comes from maternal uniparental disomy, where both copies of chromosome 15 are inherited from the mother and none from the father.
Described as modulating: Prader-Willi syndrome.
“It is caused by absence of expression of the paternally active genes in the PWS critical region on 15q11-q13.”
How to read the evidence labels
Where this comes from
This guide is built from 16 published source(s). Every claim above links back to one of them. Click any source ID to read the original on PubMed.
Take it further
Printed, source-linked documents built from this condition's graph — ready to bring to an appointment or attach to a coverage request. Every claim carries its published source, the same as this guide.