Prader-Willi Syndrome

(Named for Andrea Prader, Swiss pediatrician, born 1919; and Heinrich Willi, Swiss pediatrician, 1900–1971)

Prader-Willi syndrome
A congenital (present from birth) disease characterized by obesity, decreased muscle tone, decreased mental capacity, and hypogonadism.

Mental retardation is common. It can be caused by a deletion of chromosome 15 inherited from the father; the same deletion inherited from the mother causes Angelman's syndrome which is an autosomal recessive syndrome characterized by jerky puppetlike movements, frequent laughter, mental and motor retardation; as well as, peculiar open-mouthed faces, and seizures.

Andrea Prader and Heinrich Willi were Swiss pediatricians. Prader was a professor of pediatrics in Zurich. His articles and chapters in textbooks dealt with such topics as genetics, growth, endocrinology, and metabolism in children and adolescents. Prader and Willi first described the Prader-Willi syndrome in 1956. Cases of the disorder were not diagnosed in the United States until the 1960s.

The causes of PWS or Prader-Willi syndrome

Prader-Willi is caused by the deletion of a gene on chromosome 15. The majority of patients have a deletion of the father's DNA in this region. The remaining patients frequently have two copies of the mother's chromosome 15. The maternal copy of this gene is turned off in all people.

When there is a deletion of the father's DNA (approximately 70% of patients), the disease occurs. This is because the patient is left with only the inactive, maternal copy.

Signs of Prader-Willi syndrome may be seen at birth. New infants with the condition are often small and very floppy (hypotonic). Male infants may have undescended testicles. The growing child exhibits slow mental and delayed motor development, increasing obesity, and characteristically small hands and feet.

Rapid weight gain may occur during the first few years because the patient develops uncontrollable hunger which leads to morbid obesity.

Mental development is slow, and the IQ seldom exceeds 80; however, children with Prader-Willi generally are very happy, smile frequently, and are pleasant to be around.

Affected children have an intense craving for food and will do almost anything to get it. This results in uncontrollable weight gain. Morbid obesity (the degree of obesity that seriously affects health) may lead to respiratory failure with hypoxia (low blood oxygen levels), or pulmonale (right-sided heart failure), and death.

Special points regarding Prader-Willi syndrome

  • Prader-Willi syndrome (PWS) is a complex genetic disorder that typically causes low muscle tone, short stature, incomplete sexual development, cognitive disabilities, problem behaviors, and a chronic feeling of hunger that can lead to excessive eating and life-threatening obesity.
  • Most cases of Prader-Willi syndrome are attributed to a spontaneous genetic error that occurs at or near the time of conception for unknown reasons.
  • In a very small percentage of cases (two percent or less), a genetic mutation that does not affect the parent is passed on to the child, and in these families more than one child may be affected.
  • A PWS-like disorder can also be acquired after birth if the hypothalamus portion of the brain is damaged through injury or surgery.
  • The hypothalamus apparently never sends the message that the person has eaten enough and so the subject wants to keep eating way beyond his/her normal stomach capacity.
  • It is estimated that one in 12,000 to 15,000 people has PWS.
  • Although considered a "rare" disorder, Prader-Willi syndrome is one of the most common conditions seen in genetics clinics and is the most common genetic cause of obesity that has been identified.
  • PWS is found in people of both sexes and all races.
  • People with PWS have a flaw in the hypothalamus part of their brain, which normally registers feelings of hunger and satiety.
  • While the problem is not yet fully understood, it is apparent that people with this flaw never feel full; they have a continuous urge to eat that they cannot learn to control.
  • To compound this problem, the physical make-up of people with PWS actually require less food than their peers without the syndrome because their bodies have less muscle and tend to burn fewer calories.
  • The overeating associated with PWS does not begin at birth; in fact, newborns with PWS often cannot get enough nourishment because low muscle tone impairs their sucking ability.
  • Many require special feeding techniques or tube feeding for several months after birth, until muscle control improves.
  • Sometime in the following years, usually before school age, children with PWS develop an intense interest in food and can quickly gain excess weight if calories are not restricted.
  • In addition to their involuntary focus on food, people with PWS tend to have obsessive/compulsive behaviors that are not related to food; such as, repetitive thoughts and verbalizations, collecting and hoarding of possessions, picking at skin irritations, and a strong need for routine and predictability.
  • Frustration or changes in plans can easily set off a loss of emotional control in someone with PWS, ranging from tears to temper tantrums to physical aggression.
  • While psychotropic medications can help some individuals, the essential strategies for minimizing difficult behaviors in PWS are careful structuring of the person's environment and consistent use of positive behavior management and support.
—Compiled from excerpts of information found in
Management of Prader-Willi Syndrome by Merlin G. Butler, et al., Editors;
Springer Science + Business Media, Inc.; New York; 2006.

Webster's New World Medical Dictionary; Wiley Publishing, Inc.;
Hoboken, New Jersey; 2008; pages 344-345.
and snippets from a variety of other references.