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Prader-Willi syndrome

Prader-Willi syndrome is a genetic disorder in which seven genes (or some subset thereof) on chromosome 15 are missing or unexpressed (chromosome 15q partial deletion). It was identified in 1956 by Andrea Prader, Heinrich Willi, Alexis Labhart, and Guido Fanconi of Switzerland. more...

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Symptoms

Prader-Willi syndrome (PWS) is characterized by:

  • Severe hypotonia and feeding difficulties in early infancy.
  • Excessive eating and gradual development of morbid obesity in later infancy or early childhood, unless externally controlled.
  • Mental retardation and distinctive behavioral problems in all patients.
  • Hypogonadism is present in both males and females.
  • Short stature is common.

Diagnosis/testing

Accurate consensus clinical diagnostic criteria exist, but the mainstay of diagnosis is genetic testing, specifically DNA-based methylation testing to detect the absence of the paternally contributed Prader-Willi syndrome/Angelman syndrome (PWS/AS) region on chromosome 15q11.2-q13. Such testing detects over 99% of patients. Methylation-specific testing is important to confirm the diagnosis of PWS in all individuals, but especially those who are too young to manifest sufficient features to make the diagnosis on clinical grounds or in those individuals who have atypical findings.

Genetics

PWS is caused by absence of the paternally derived PWS/AS region of chromosome 15 by one of several genetic mechanisms, including uniparental disomy, imprinting mutations, chromosome translocations, and gene deletions. The genes responsible for Prader-Willi syndrome are expressed only on the paternal chromosome. (Interestingly, a deletion on the maternal chromosome causes Angelman syndrome.) This is the first known instance of imprinting in humans.

The risk to the sibling of an affected child of having PWS depends upon the genetic mechanism which caused the disorder. The risk to siblings is <1% if the affected child has a gene deletion or uniparental disomy, up to 50% if the affected child has a mutation of the imprinting control center, and up to 25% if a parental chromosomal translocation is present. Prenatal testing is possible for any of the known genetic mechanisms.

Read more at Wikipedia.org


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Hunger hormone gone awry? - Obesity - Ghrelin and Prader-Willi syndrome - Brief Article
From Science News, 7/6/02

People with Prader-Willi syndrome, a genetic disorder that causes constant hunger and severe obesity, have unusually high concentrations of a hormone called ghrelin, which has been linked to hunger pangs.

"These patients have higher ghrelin levels than recorded in any other humans," says David E. Cummings of the University of Washington in Seattle. Among 18 people with Prader-Willi syndrome, blood concentrations of ghrelin were 4.5 times those in blood from people of similar weights but free of the syndrome, he says.

Ghrelin concentrations were only about 2.5 times as high in people with Prader-Willi syndrome as in healthy nonobese individuals. Cummings says that ghrelin concentrations are higher in nonobese people than in obese people. The reason, he speculates, is that the overweight body attempts to reduce appetite by producing less of the hormone.

Hunger regulation is completely awry in people with the syndrome, who tend to be slightly underweight just after birth but soon develop uncontrollable cravings for food. "They will eat anything--feces, fingers, dirt--and if untreated will die from complications of obesity before age 30," Cummings says.

This research joins a growing body of evidence implicating ghrelin as the major biochemical cause of hunger (SN: 2/16/02, p. 107; 6/8/02, p. 366). That makes the hormone a promising target for drugs designed to boost appetite among people with cancer, AIDS, and other wasting syndromes, as well as for a drug that might help people curb their appetites.--D.C.

COPYRIGHT 2002 Science Service, Inc.
COPYRIGHT 2002 Gale Group

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