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What is Prader-Willi Syndrome

Below you will find a complete explanation of PWS, its causes, and options for treatment.

What is PWS

Prader-Willi syndrome (PWS) is a genetic disorder involving a defect on the 15th chromosome and subsequent dysfunction of the brain structure (hypothalamus) responsible for hunger. PWS initially presents as a failure to thrive at birth, and then evolves into an insatiable appetite with onset usually between the ages of 2 and 4. If access to food is not adequately supervised, this inability to feel satiated can lead to potentially life-threatening medical conditions associated with obesity.

In addition to the intense drive to eat, individuals with PWS usually have metabolic dysfunction, low muscle tone (hypotonia), incomplete sexual development, cognitive and learning disabilities, neurological manifestations and significant emotional and behavioral challenges.

It is estimated that Prader-Willi syndrome occurs in 1 of 15,000 births, with equal frequency in males and females across all races.

Most Common Characteristics/Symptoms

There are two stages identified in Prader-Willi Syndrome, with the following characteristics typically observed at each stage:

  • Failure to Thrive (during the first year or so of life)
  • Low birth weight/poor weight gain
  • “Floppy baby” syndrome or weak muscle tone (hypotonia)
  • Poor sucking reflexes
  • Need for adaptive feeding devices
  • Delayed motor development: sitting, crawling, walking and speech
  • Underdeveloped genitals (hypogonadism)

Thriving Too Well (usually begin between 2-4 years of age)

  • Insatiable appetite (hyperphagia), compulsive eating and obsession with food
  • Obesity (resulting from hyperphagia, hypotonia, need for fewer calories and decreased metabolism)
  • Behavior problems such as stubbornness and temper tantrums (usually begin during preschool years)
  • Learning disabilities or cognitive delays (in the mild-moderate range, with an average IQ in the 70’s and ranging between 35-105)
  • Speech and language problems
  • Poor social skills/interactions

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Physical Characteristics Persisting into Adulthood

  • Short stature
  • Small hands and feet
  • Pear-shaped body
  • Waddling gait
  • Pickwickian Syndrome (falling asleep suddenly)
  • Hip and joint problems
  • Scoliosis (lateral curvature of the spine)
  • Myotonia (prolonged muscle spasm)
  • Incomplete sexual development
  • Obesity, which may result in further health problems
  • Susceptibility to potential respiratory and heart problems
  • Almond-shaped eyes
  • Narrow face
  • Small, down-turned mouth
  • Thick saliva
  • Sleep disturbance/sleep apnea
  • Abnormal body temperature regulation
  • Increased pain tolerance
  • Skin Picking
  • Hypopigmentation and associated sensitivity to sunlight
  • Cross-eyed (esotropia)/nearsighted (myopia)

Behavioral Characteristics Persisting into Adulthood

  • Unpredictable and erratic behavior
  • Rage or other aggressive outbursts
  • Mood disorders
  • Obsessive-compulsive tendencies and behaviors
  • Stubborn
  • Argumentative
  • Manipulative
  • Possessive
  • Food seeking/foraging for food
  • Stealing, particularly related to food
  • Oppositional and defiant behaviors
  • Rigid thought process



The specific cause of Prader-Willi syndrome is unclear. However, normally it is the result of genetic material absent from a section of the father’s chromosome 15. There are three different ways this can occur:

  • About 70% of the cases are attributed to paternal deletion (part of chromosome 15 from the father is missing).
  • Approximately 30% of those with Prader-Willi Syndrome have maternal uniparental disomy (UPD) (both copies of chromosome 15 come from the mother; the father’s genetic material is thus absent).
  • The remaining 1-3% of cases are associated with an imprinting defect (genes on the father’s chromosome 15 are present but do not work).
  • An individual can acquire symptoms similar to those manifested in PWS by trauma to the hypothalamus through tumor, injury, or damage.

Chromosome 15 controls the hypothalamus, the part of the brain that regulates body temperature and water balance; controls appetite; and influences blood pressure, sexual behavior, aggression, fear and sleep. The hypothalamus also controls the pituitary gland (ultimately affecting growth, sexual development and metabolism). There is also a direct relationship with the pineal gland which regulates body cycles, sleep cycles and the onset of sleep. The current school of thought says that in individuals with Prader-Willi syndrome, the hypothalamus is not working properly and the functions it controls are therefore affected.

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PWH provides a living environment in which each individual is valued and provided with the opportunity to explore their highest potential of independence within a safe, supportive and therapeutic environment.

Individuals diagnosed with Prader-Willi syndrome do much better in a highly structured living environment. Carefully controlled diets, structured access to food, and regular exercise are central to managing weight gain. Occupational therapy may be helpful in promoting motor development and improving hypotonia. Early and ongoing speech therapy can benefit individuals with speech and language problems.

Individuals diagnosed with Prader-Willi syndrome are better with concrete concepts (such as jigsaw puzzles and word search games) rather than abstract ideas. Visual and demonstration methods used for teaching activities are more helpful and effective than simply relating information verbally. These concepts are incorporated into our program services.

We provide treatment for individuals with Prader-Willi syndrome within a highly structured daily routine and activity schedule: 24-hour support and supervision, strict dietary monitoring, and positive motivational approaches to behavior management.

Though individuals diagnosed with Prader-Willi syndrome have multiple and complex needs, the prognosis and treatment is favorable when done in a structured setting. Behavioral, psychological, emotional and personality characteristics of individuals with Prader-Willi syndrome are areas that require ongoing support and management.

We offer an array of programs and services, including individual treatment plans, vocational and educational programming, independent living skills training, psychiatric and psychological consultation, motivational systems, dietician consultation and exercise programming, community integration and socialization opportunities, and case management.

Staff at PWH recognize that each person is unique with individual strengths and needs. Our priority is always the well-being of each person. If we determine that PWH cannot offer the very best care and treatment, we are happy to help facilitate placement in another facility.