Prader-Willi Syndrome

Prader-Willi syndrome is a rare genetic disorder that transforms through a person’s lifetime—beginning with weak, floppy infants who struggle to feed, then shifting dramatically in childhood to an insatiable appetite that never signals fullness, leading to one of the most challenging aspects of care: constant food supervision to prevent life-threatening obesity.

Table of contents

• What is Prader-Willi syndrome?
• How common is the condition?
• What causes Prader-Willi syndrome?
• Symptoms throughout life stages
• Physical characteristics
• How is it diagnosed?
• Treatment and management
• Long-term outlook

What is Prader-Willi syndrome?

Prader-Willi syndrome (PWS) is a rare genetic condition that affects many parts of the body. It was first described in 1956 by Swiss doctors Andrea Prader, Alexis Labhart, and Heinrich Willi, who examined nine children with similar characteristics^[1].

The condition causes problems with metabolism (how the body processes food and energy), growth, behavior, and learning. A key feature of PWS is hyperphagia, which means an unending appetite where people never feel full after eating^[2]. This constant hunger typically appears between ages 3 and 8, though the timing varies^[1].

PWS is recognized as the most common genetic cause of life-threatening childhood obesity. The symptoms are believed to result from dysfunction of the hypothalamus, a small organ at the base of the brain that controls hunger and satiety, body temperature, pain, sleep-wake balance, fluid balance, emotions, and fertility^[1]. Although researchers know the hypothalamus doesn’t work properly in PWS, it’s not yet clear exactly how the genetic abnormality causes this dysfunction.

How common is the condition?

Prader-Willi syndrome occurs in approximately one out of every 15,000 births^[1]. Some estimates suggest it may affect between 1 in 10,000 to 30,000 people worldwide^[2][3].

PWS affects males and females with equal frequency and occurs in all races and ethnicities^[1]. More than 400,000 people worldwide are estimated to live with the condition^[6].

What causes Prader-Willi syndrome?

Prader-Willi syndrome results from an abnormality of chromosome 15. At conception, you inherit one copy of chromosome 15 from each biological parent. The copy from the father (the paternal copy) is the only one that activates or turns on. The copy from the mother (the maternal copy) is turned off. Both copies are necessary for genes to get the instructions the body needs to function properly. This process is called genomic imprinting^[3].

There are three main causes of this genetic change to chromosome 15:

• Chromosomal deletion: Nearly 70% of all PWS cases occur when part of the paternal chromosome 15 is missing in each cell. Symptoms arise because the paternal copy of chromosome 15 is missing or not working properly and the maternal copy is turned off^[3][7].
• Maternal uniparental disomy: About 25% of PWS cases happen when a child inherits two maternal copies of chromosome 15 instead of one from each biological parent. This means both copies of chromosome 15 don’t work because they’re both inactive^[3][7].
• Translocation or imprinting defect: Less than 1% of all cases occur when a piece of chromosome 15 relocates itself to another chromosome, or when a genetic alteration abnormally turns off genes on the paternal chromosome 15^[3][7].

Chromosome 15 is responsible for providing instructions for making small nucleolar RNAs (snoRNAs). Studies suggest that the loss of a particular group of snoRNA genes, known as the SNORD116 cluster, may play a major role in causing the signs and symptoms of Prader-Willi syndrome^[7].

PWS is not generally inherited, but rather the genetic changes happen during the formation of the egg, sperm, or in early development. Anyone can develop Prader-Willi syndrome because it’s a genetic condition that happens randomly when reproductive cells form^[3][6]. Those who have one child with PWS have less than a 1% chance of the next child being affected^[6].

Symptoms throughout life stages

The symptoms of Prader-Willi syndrome change over time as a person grows from infancy through adulthood. A detailed understanding of the nutritional stages of PWS has been published to help families and healthcare providers know what to expect^[1].

Early life and infancy

Infants with PWS are hypotonic or “floppy”, with very low muscle tone. Babies may rest with their elbows and knees loosely extended instead of fixed, and they may feel floppy or like rag dolls when held^[1][2].

A weak cry and a poor suck reflex are typical. Babies with PWS usually are unable to breastfeed and frequently require tube feeding^[1][2]. These infants may suffer from “failure to thrive” if feeding difficulties are not carefully monitored and treated. Babies may seem very tired, respond poorly to stimulation, have a hard time waking up, or cry weakly^[2].

As these babies grow older, strength and muscle tone generally improve. Motor milestones are achieved, but are usually delayed^[1].

Childhood and beyond

Toddlers typically enter a period where they may begin to gain weight easily, prior to having a heightened interest in food^[1]. An unregulated appetite (hyperphagia) and easy weight gain characterize the later stages of PWS. These features most commonly begin between ages 3 and 8 years old, but are variable in onset and intensity^[1].

Individuals with PWS lack normal hunger and satiety cues. They usually are not able to control their food intake and will overeat if not closely monitored^[1]. Food seeking behaviors are very common. In addition, the metabolic rate of persons with PWS is lower than normal^[1]. This means people with PWS burn up less energy, and need fewer calories and less food than other people^[8].

Left untreated or in an unrestricted environment, this combination of problems often leads to morbid obesity and its many complications^[1].

Developmental and behavioral symptoms

Individuals usually exhibit cognitive challenges, with measured IQs ranging from low normal to moderate intellectual disability (problems with thinking and learning). Those with normal IQs usually exhibit learning disabilities^[1][7].

Behavioral difficulties may include obsessive-compulsive symptoms, skin picking, and difficulty controlling emotions. Temper tantrums, emotional outbursts, or stubbornness are common^[1][3][7].

Other health issues

Additional issues may include growth hormone deficiency and short stature, small hands and feet, scoliosis (curved spine), sleep disturbances with excessive daytime sleepiness, high pain threshold, speech problems, and infertility^[1].

PWS typically also causes a delay in puberty. Both affected males and affected females have underdeveloped genitals. Males may have a small penis and scrotum. Puberty is delayed or incomplete, and most affected individuals are unable to have children^[2][7].

Physical characteristics

People with Prader-Willi syndrome often have distinctive facial features and other physical characteristics. These may include:

• Almond-shaped eyes
• A narrowing of the head at the temples or a narrow forehead
• A turned-down mouth or triangular mouth
• A thin upper lip
• A long, narrow head
• Short height (short stature)
• Small hands and feet

Some people with Prader-Willi syndrome have unusually fair skin and light-colored hair. This is associated with the loss of a gene called OCA2, which is located on the segment of chromosome 15 that is often deleted in people with this disorder. The protein produced from this gene helps determine the coloring of the skin, hair, and eyes^[7].

How is it diagnosed?

A suspected diagnosis of Prader-Willi syndrome is usually made by a physician based on clinical symptoms. PWS should be suspected in any infant born with significant hypotonia (muscle weakness or “floppiness”) and difficulty feeding^[12].

Typically, healthcare professionals suspect Prader-Willi syndrome based on symptoms. The diagnosis is confirmed through genetic testing^[9]. This blood test can find problems in a child’s chromosomes that suggest Prader-Willi syndrome.

The preferred method of testing is a “methylation analysis,” which detects more than 99% of cases, including all of the major genetic subtypes of PWS (deletion, uniparental disomy, or imprinting mutation)^[12]. A “FISH” (fluorescent in-situ hybridization) test will identify those patients with PWS due to a deletion, but it will not identify those who have Prader-Willi syndrome by uniparental disomy or an imprinting error.

Genetic testing may be recommended if a child has the symptoms of Prader-Willi syndrome. Babies who are very floppy at birth may also be tested^[8].

Treatment and management

Currently, there is no cure for PWS. The lives of individuals with PWS can be improved with an early diagnosis and careful management of symptoms^[12]. Treatment aims to ease some of the associated problems and improve quality of life^[8].

Early diagnosis and treatment can make quality of life better for people with Prader-Willi syndrome. A team of health professionals likely will manage the condition. A multidisciplinary approach involving genetics, endocrinology, nutrition, neurology, developmental pediatrics, behavioral health, and social services is central to supporting optimal outcomes^[4][9].

Managing weight and diet

One of the most important parts of caring for someone with Prader-Willi syndrome is to try to maintain a normal weight. They should have a healthy, balanced diet, avoiding sweet treats and high-calorie items right from the start^[8].

People with Prader-Willi syndrome can eat much more than other people and still feel hungry. Limiting food intake can be very challenging. People with PWS may become frustrated when they want extra food, and their hunger can make them hide or steal food^[8].

Dietary advice includes:

• Start good habits with a healthy diet and regular mealtimes as soon as your child starts on solid food
• Avoid sugary items, sweets and high-calorie snacks
• Give smaller portions of carbohydrates such as potatoes, rice or pasta
• Increase the amount of lower calorie foods, such as vegetables, salads and fruit
• Give a vitamin supplement

It can be difficult for a child to control their food intake themselves, so you need to keep to regular mealtimes and not allow extra portions, stop them accessing food outside of mealtimes (you may need to lock cupboards and the fridge), keep food out of their view, and make sure everyone who is in contact with them knows about the issues with food^[8][11].

Exercise

Exercise plays an important part in helping maintain a healthy weight. Children should do at least 60 minutes of exercise a day. Many people with Prader-Willi syndrome have reduced energy levels, so it may be a good idea to break down exercise into 5- to 10-minute sessions throughout the day^[11].

People with Prader-Willi syndrome usually prefer individual activities to team sports, such as swimming, walking, or exercising in a gym^[11].

Growth hormone therapy

Treatment with an artificial version of human growth hormone (HGH) is usually recommended for children with Prader-Willi syndrome. In June 2000, HGH was officially approved by the Federal Drug Administration (FDA) in the United States for use in patients with Prader-Willi syndrome^[12].

HGH is effective not only in increasing height, but also in decreasing body fat, increasing muscle mass, improving weight distribution, increasing stamina, and increasing bone mineral density. In addition, studies suggest its positive effects on development and behavior^[12].

Starting treatment with HGH is usually recommended during early childhood, from 6 months to 2 years of age^[11]. HGH increases muscle size while lowering the amount of body fat, increases muscle strength, should increase energy levels, and helps change facial appearance, making the distinctive facial features associated with Prader-Willi syndrome less noticeable^[11].

Hormone replacement therapy

Your child’s doctor may suggest hormone replacement therapy because of low levels of sex hormones. This means testosterone for males or estrogen and progesterone for females^[9].

Medication for hyperphagia

In March 2025, the US Food and Drug Administration approved diazoxide choline (Vykat XR) as the first drug for the treatment of hyperphagia in Prader-Willi syndrome. It is indicated for adults and for children aged 4 years or older^[14].

Early intervention and therapy

Many infants with Prader-Willi syndrome have a hard time feeding because they have less muscle tone. Healthcare professionals may recommend a high-calorie formula or special feeding methods to help babies gain weight^[9].

Implementation of early intervention therapies is important, which may include occupational, physical, and speech therapy^[19].

Support and supervision

Strict food supervision is typically required, starting around the age of three, in combination with an exercise program. Counseling and medications may help with some behavioral problems. Group homes are often necessary in adulthood^[6].

Long-term outlook

Prader-Willi syndrome itself is not life-threatening. However, compulsive eating and weight gain can cause young adults with the syndrome to develop serious obesity-related conditions such as type 2 diabetes, heart failure, and breathing difficulties^[8].

If diet is well controlled and people do not become overweight, adults can have a good quality of life and probably a normal life expectancy^[8]. Many adults with Prader-Willi syndrome take part in activities such as voluntary or part-time work, but it’s unlikely they’ll be able to live fully independent lives^[8].

Although rare, life-threatening complications can occur and include respiratory illnesses, obesity-related cardiovascular problems, sleep apnea and diabetes^[3]. The increased appetite also means there’s a higher risk of choking on food, so carers are advised to learn what to do if someone is choking^[8].

• Hypothalamus
• Brain
• Chromosome 15

Prader-Labhart-Willi-Fanconi syndrome