Prader-Willi Syndrome (PWS) is a genetic disorder characterized by neurological impairments causing an unusual pattern of
growth and development related to an abnormally increased appetite with an excessive need for food consumption. Prader-
Willi Syndrome affects 1:12,000 -15,000 live births and is found in both genders and all races.

Physical characteristics of PWS include short stature, small hands and feet, and a characteristic facial appearance consisting
of a thin upper-lip, down-turned mouth, dental crowding, and almond shaped eyes. Developmental milestones are delayed,
and learning disabilities are always present, but may vary in severity. Behavioral problems include temper tantrums, obsessive
compulsive tendencies, and skin-picking. Its characteristics also include loss of muscular strength, uncontrolled appetite,
obesity, delayed pubescence; variable degrees of mental retardation or functional retardation. Sexual development may occur
early or late, but it is usually incomplete. Individuals with PWS do not undergo spontaneous pubertal development and are

The stress on families is often immense. The constant pressure of food control and behavior management affects all family
members, such as higher divorce rates and siblings with emotional problems. The child with PWS can become a dictator who
rules the family and, with age, becomes more difficult to handle. Recognition of the strains and dealing with them early on is
essential to the family’s vitality.

Areas of Development     

Children with Prader-Willi show developmental delays in all areas typically by one to two years behind children of the same
age. For example, walking usually occurs at about age two. Gross motor and balance are difficult skills for them to master
but are goals that slowly but surely will be achieved. Speech and language difficulty is common, although the cause is not
quite clear. Speech therapy is beneficial to ease the frustration with any communication deficiency. Though language
development is delayed, verbal ability is often a strong. However, articulation may remain weak. Logical thinking and
concepts (the idea of putting a plan into effect) are impaired. The average IQ is around 70, with a range from 40 to 105. Even
with a lower IQ, cleverness in finding food can occur.

Behavioral problems, ranging from stubbornness to violent temper tantrums which increase with age, usually begin to appear
during the preschool years. Other common characteristics include a high pain threshold, dental problems, and breathing
difficulties. Medical intervention therapy can be used to modify the severity of violent tantrums (e.g., fluexitine serotonin
uptake inhibitors have been helpful in some cases). Other conditions such as depression and psychotic episodes have been
reported. Medications in most cases have not been found generally useful in controlling appetite. Drug treatment is essential at
times but is not recommended for permanent use. Consult the national PWSA office or speak with your child’s physician for
updates and information.

Motor skills like sports activities are limited. Running and jumping can cause joint injuries due to poor muscle strength and
coordination. There are occurrences of bone fracture, possibly related to fragile bones and decreased muscle mass. Adaptive
physical exercise is necessary during school years. Walking, swimming, and stationary exercise equipment are recommended.
Most cases of children with Prader-Willi syndrome become apparent to parents and physicians because of their motor
development (poor muscle tone), developmental delay, and/or obesity as infants.

Adults with PWS can function well in assisted living facilities with adequate control over food intake and a structured living
setting. Their difficult personalities and explosive tempers make supervision and counseling hard. Adults may lead a
productive life in a group setting with opportunity in light industrial workshops which offer the best employment possibilities.

Weight Control and Obesity

Obsessive eating and a fixation with food usually begin between the ages of 2 to 4, although it may present later on. Some
children learn to eat at set times and may refuse certain foods, but the craving for food in general will always persist.
Sneaking or stealing extra food is typical. In most situations, all sources of food must be kept under lock and key. This may
involve uncommon discipline such as locking the refrigerator or kitchen cabinets. Avoid purchasing foods that are tempting
and fattening.

Obesity occurs in 95% of cases if there is no supervision over the amount of food absorption. About two-thirds of individuals
cannot vomit even after consumption of spoiled food or other foul substances. An increasing number of children with PWS
are being diagnosed before an onset of obesity. Whether obese at diagnosis or not, more and more have their weight managed
within acceptable numbers. Calculation of calories and exercise are critical to weight control and obesity.

Possible Causes

The first patients with characteristics of Prader-Willi Syndrome were described by Dr. Prader, Dr. Willi, and Dr. Lambert in
1956. Initially, scientists found that individuals with PWS have a region of genetic matter deleted (erased) from chromosome
15. In order to have PWS, the genetic matter must be deleted from the chromosome 15 received from one's father. If the
deletion is on the chromosome 15 inherited from one's mother a different syndrome develops. This important discovery
proved for the first time that the genes inherited from one's mother can be perceived differently than the genes inherited from
one's father.

As more cases emerged scientist concluded that some individuals with PWS did not have deleted genetic matter from
chromosome 15. Further studies found that these patients inherit both copies of chromosome 15 from their mother. This is
not typical. Normally, an individual receives one chromosome 15 from their father and one chromosome 15 from their
mother. When a person receives both chromosomes from the same parent it is called "uniparental disomy” (UPD).

Scientists are still discovering other causes of PWS. A small number of patients with PWS have a change (mutation) in the
genetic matter on the chromosome 15 inherited from their father. This mutation prevents certain genes on chromosome 15
from working properly. PWS develops when these genes do not work regularly.

Prader-Willi syndrome is caused by a deficiency in the crucial area of chromosome 15. Nearly 70% have an imperfection and
other abnormal findings in chromosome 15, which is detected by using high resolution cell and chromosome analysis. PWS is
an impressionable disorder caused by a faulty connection in the paternal copy of chromosome15. There is a 50% chance of
having more than one child with the disorder; it all depends on gene formation.   

Making a Diagnosis

During infancy the diagnosis of PWS may be noticeable due to poor muscle tone, feeding problems, small genitalia, or the
unique facial features are present. If an infant has these features, testing for PWS should be performed. This testing should
also be offered to children and adults who display features commonly seen in PWS (developmental delay, uncontrollable
appetite, small genitalia, etc.). There are several different genetic tests that can detect PWS. All of these tests can be
performed from a blood sample.

Methylation testing detects 99% of the cases of PWS. Methylation testing can detect the absence of the paternal genes that
should be normally active on chromosome 15. Although methylation testing can accurately diagnose PWS, it can not
determine if the PWS is caused by a deletion, maternal uniparental disomy (UPD), or a mutation that disrupts imprinting. This
information is important for genetic counseling. Therefore, additional testing should be performed.

PWS can be detected before birth if the mother undergoes amniocentesis testing or chorionic villus sampling (CVS). This
testing is only recommended if the mother or father is known to have a chromosome rearrangement, or if they already have a
child with PWS syndrome.


At this time there is no cure for PWS. Early interventions like physical therapy help improve muscle tone. Some infants with
PWS also require special nipples and feeding techniques to improve weight gain.

Treatment and management during childhood, adolescence, and adulthood is generally focused on weight control. Strict
control of food intake is necessary to prevent obesity. A lifelong restricted calorie diet and a regular exercise program are also
advised. Unfortunately, diet medications have not been shown to significantly prevent obesity in PWS. However, growth
hormone therapy has been shown to improve the poor muscle tone and reduced height typically associated with PWS.

Special education may be helpful in treating developmental delays and behavior problems. Individuals with PWS typically
excel in highly structured environments. Early intervention with a dietitian and behavioral psychologist to prevent excessive
weight gain in childhood is important. With appropriate interventions and ongoing support, people with Prader-Willi Syndrome
live a normal life expectancy. Most adults live with family or in accommodation with various interventions.
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