Prader-Willi syndrome

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Other Names: PWS; Willi-Prader syndrome; Prader-Labhart-Willi syndrome

Prader-Willi syndrome (PWS) is a genetic condition that affects many parts of the body. Infants with PWS have severe hypotonia (low muscle tone), feeding difficulties, and slow growth. In later infancy or early childhood, affected children typically begin to eat excessively and become obese. Prader-Willi syndrome is a complex genetic condition that affects many parts of the body. In infancy, this condition is characterized by weak muscle tone (hypotonia), feeding difficulties, poor growth, and delayed development. Beginning in childhood, affected individuals develop an insatiable appetite, which leads to chronic overeating (hyperphagia) and obesity. Some people with Prader-Willi syndrome, particularly those with obesity, also develop type 2 diabetes




Prader-Willi syndrome (PWS) is caused by the loss of active genes in a specific region of chromosome 15. People normally inherit one copy of chromosome 15 from each parent. Some genes on chromosome 15 are only active (or "expressed") on the copy that is inherited from a person's father (the paternal copy). When genes are only active if inherited from a specific parent, it is called genomic imprinting.

About 70% of cases of PWS occur when a person is missing specific genes on the long arm of the paternal copy of chromosome 15. This is called a deletion. While there are copies of these same genes on the maternal copy of chromosome 15, the maternal copies of these genes are not expressed.

In about 25% of cases, PWS is due to a person inheriting only 2 maternal copies of chromosome 15, instead of one copy from each parent. This is called maternal uniparental disomy.

Rarely (in about 2% of cases), PWS is caused by a rearrangement of chromosome material called a translocation, or by a change (mutation) or other defect that abnormally inactivates genes on the paternal chromosome 15.

Each of these genetic changes result in a loss of gene function on part of chromosome 15, likely causing the characteristic features of PWS.


Most cases of Prader-Willi syndrome are not inherited, particularly those caused by a deletion in the paternal chromosome 15 or by maternal uniparental disomy. These genetic changes occur as random events during the formation of reproductive cells (eggs and sperm) or in early embryonic development. Affected people typically have no history of the disorder in their family.

Rarely, a genetic change responsible for Prader-Willi syndrome can be inherited. For example, it is possible for a genetic change that abnormally inactivates genes on the paternal chromosome 15 to be passed from one generation to the next.


In infancy, Prader-Willi syndrome (PWS) is characterized by weak muscle tone (hypotonia), feeding difficulties, poor growth, and delayed development. In later infancy or early childhood, affected children develop an extreme appetite, which leads to overeating and obesity. Other signs and symptoms of PWS may include:

  • mild to moderate intellectual disability
  • sleep abnormalities
  • unusually fair skin
  • underdeveloped genitals
  • delayed or incomplete puberty
  • short stature
  • strabismus
  • scoliosis
  • small hands and feet
  • distinctive facial features such as a narrow forehead, almond-shaped eyes, and a triangular mouth
  • Behavioral problems are common and often include temper tantrums, stubbornness, and obsessive-compulsive tendencies.


In many cases of Prader-Willi syndrome, diagnosis is prompted by physical symptoms in the newborn. If a newborn is unable to suck or feed for a few days and has a "floppy" body and weak muscle tone, a health care provider may conduct genetic testing for Prader-Willi syndrome.

Children younger than 3 years must have at least four major criteria and at least one minor criterion for a Prader-Willi syndrome diagnosis.

Those older than 3 years must have at least five major criteria and at least three minor criteria for a diagnosis of Prader-Willi syndrome.

Major Clinical Criteria of Prader-Willi Syndrome

  • Extremely weak muscles in the body's torso
  • Difficulty sucking, which improves after the first few months
  • Feeding difficulties and/or failure to grow, requiring feeding assistance, such as feeding tubes or special nipples to aid in sucking
  • Beginning of rapid weight gain, between ages 1 and 6, resulting in severe obesity
  • Excessive, uncontrollable overeating
  • Specific facial features, including narrow forehead and downturned mouth
  • Reduced development of the genital organs, including small genitalia (vaginal lips and clitoris in females and small scrotum and penis in males); incomplete and delayed puberty; infertility
  • Developmental delays, mild-to-moderate intellectual disability, multiple learning disabilities

Minor Clinical Criteria of Prader-Willi Syndrome

  • Decreased movement and noticeable fatigue during infancy
  • Behavioral problems-specifically, temper tantrums, obsessive-compulsive behavior, stubbornness, rigidity, stealing, and lying (especially related to food)
  • Sleep problems, including daytime sleepiness and sleep disruption
  • Short stature, compared with other members of the family, noticeable by age 15
  • Light color of skin, eyes, and hair
  • Small hands and feet in comparison to standards for height and age
  • Narrow hands
  • Nearsightedness and/or difficulty focusing both eyes at the same time
  • Thick saliva
  • Poor pronunciation
  • Picking of the skin
  • Additional Findings
  • High pain threshold
  • Inability to vomit
  • Curvature of the spine (scoliosis)
  • Earlier-than-usual activity in the adrenal glands, which can lead to early puberty
  • Especially brittle bones (called osteoporosis, pronounced os-tee-oh-puh-ROH-sis)

Genetic testing must confirm the Prader-Willi syndrome diagnosis. Almost all individuals with Prader-Willi syndrome have an abnormality within a specific area of chromosome 15.Early diagnosis is best because it enables affected individuals to begin early intervention/special needs programs and treatment specifically for Prader-Willi symptoms. However, the current mainstay of a diagnosis when PWS is suspected is a form of genetic testing called DNA methylation testing. This testing can detect abnormal, parent-specific imprinting on the region of chromosome 15 that is responsible for PWS. It determines whether the region is maternally inherited only (i.e., the paternally contributed region is absent) and confirms a diagnosis in more than 99% of affected people. DNA methylation testing is especially important in people who have non-classic features, or are too young to show enough features to make the diagnosis based on signs and symptoms alone.


Parents can enroll infants with PWS in early intervention programs. However, even if a PWS diagnosis is delayed, treatments are valuable at any age.

The types of treatment depend on the individual’s symptoms. The health care provider may recommend the following:

Use of special nipples or tubes for feeding difficulties Difficulty in sucking is one of the most common symptoms of newborns with Prader-Willi syndrome. Special nipples or tubes are used for several months to feed newborns and infants who are unable to suck properly, to make sure that the infant is fed adequately and grows.

Strict supervision of daily food intake Once overeating starts between ages 2 and 4 years, supervision will help to minimize food hoarding and stealing and prevent rapid weight gain and severe obesity. A well-balanced, low-calorie diet and regular exercise are essential and must be maintained for the rest of the individual's life. People with PWS rarely need more than 1,000 to 1,200 calories per day.

Growth Hormone (GH) therapy GH therapy has been demonstrated to increase height, lean body mass, and mobility; decrease fat mass; and improve movement and flexibility in individuals with PWS from infancy through adulthood.

Treatment of eye problems by a pediatric ophthalmologist Many infants have trouble getting their eyes to focus together. These infants should be referred to a pediatric ophthalmologist who has expertise in working with infants with disabilities.

Treatment of curvature of the spine by an orthopedist An orthopedist should evaluate and treat, if necessary, curvature of the spine (scoliosis).

Sleep studies and treatment Sleep disorders are common with PWS. Treating a sleep disorder can help improve the quality of sleep.

Physical therapy

Muscle weakness is a serious problem among individuals with PWS. For children younger than age 3, physical therapy may increase muscular strength and help such children achieve developmental milestones.

Behavioral therapy

People with PWS have difficulty controlling their emotions.

Medications Medications, especially [[]]serotonin reuptake inhibitors (SRIs), may reduce obsessive-compulsive symptoms. SRIs also may help manage psychosis.

Sex hormone treatments and/or corrective surgery These treatments are used to treat small genitals (penis, scrotum, clitoris).

Replacement of sex hormones Replacement of sex hormones during puberty may result in development of adequate secondary sex characteristics (e.g., breasts, pubic hair, a deeper voice).

Placement in group homes during adulthood

Group homes offer necessary structure and supervision for adults with PWS, helping them avoid compulsive eating, severe obesity, and other health problems.

The medication(s) listed below have been approved by the Food and Drug Administration (FDA) as orphan products for treatment of this condition.

  • Somatropin (r-DNA) for injection (Brand name: Genotropin)Long-term treatment of pediatric patients who have growth failure due to Prader-Willi syndrome (PWS).


Children with Prader-Willi syndrome (PWS) can be mainstreamed into the classroom environment, although they need additional speech therapy and should have additional physical activity periods in place of rest periods. They generally need a structured environment and may need a smaller classroom size for individual attention. People with PWS usually reach adulthood and are able to function in a group home setting, performing vocational work, or attending community college classes.According to the Prader-Willi Syndrome Association, people with PWS can expect to accomplish many of the things their peers do. However, they do need a significant amount of support from their families and from school, work, and residential service providers. Even those with IQs in the normal range need lifelong diet supervision and protection from food availability.

Complications that could affect the quality of life and potentially shorten life expectancy include those relating to hypogonadism, behavioral or psychological issues, and morbid obesity.

NIH genetic and rare disease info

Prader-Willi syndrome is a rare disease.


WikiMD Resources - Prader-Willi syndrome

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