Prader-Willi Syndrome

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Prader-Willi syndrome

is a disorder in which a person cannot stop themselves from eating. Someone with this condition will often steal, hide food or eat the pet's food. Mental retardation, friendliness, lack of muscular tone, obesity, short stature, incomplete sexual development and a stubborn attitude are other common factors in someone with this disorder.


The insatiable appetite of someone with Prader-Willi syndrome is a congenital condition, (meaning it was present at birth), and is caused by an abnormality in the genes.

This constant need for food that is seen in Prader-Willi syndrome is caused by a defect found in the hypothalamus. This part of the brain determines the hunger of a person, and with this defect, the person can never achieve a state of complete fullness.

For example, a person with PW syndrome may consume a regular sized meal, and feel as though they have barely eaten anything. It varies with different people, but it is very rare that an individual will not register any consumption of food at all.


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 some form of Diabetes.

People with Prader-Willi syndrome typically have mild to moderate intellectual impairment and learning disabilities. Behavioral problems are common, including temper outbursts, stubbornness, and compulsive behavior such as picking at the skin, hair pulling or other Body Focused Repetitive Behaviours. Sleep abnormalities- such as insomnia- can also occur.

Prader-Willi syndrome affects an estimated 1 in 10,000 to 30,000 people worldwide.


An excerpt from on the genetic aspects of Prader-Willi syndrome;

Prader-Willi syndrome is caused by the loss of function of genes in a particular region of chromosome 15. People normally inherit one copy of this chromosome from each parent. Some genes are turned on (active) only on the copy that is inherited from a person's father (the paternal copy). This parent-specific gene activation is caused by a phenomenon called genomic imprinting.

Most cases of Prader-Willi syndrome (about 70 percent) occur when a segment of the paternal chromosome 15 is deleted in each cell. People with this chromosomal change are missing certain critical genes in this region because the genes on the paternal copy have been deleted, and the genes on the maternal copy are turned off (inactive). In another 25 percent of cases, a person with Prader-Willi syndrome has two copies of chromosome 15 inherited from his or her mother (maternal copies) instead of one copy from each parent. This phenomenon is called maternal uniparental disomy. Rarely, Prader-Willi syndrome can also be caused by a chromosomal rearrangement called a translocation, or by a mutation or other defect that abnormally turns off (inactivates) genes on the paternal chromosome 15.

It appears likely that the characteristic features of Prader-Willi syndrome result from the loss of function of several genes on chromosome 15. Among these are genes that provide instructions for making molecules called small nucleolar RNAs (snoRNAs). These molecules have a variety of functions, including helping to regulate other types of RNA molecules. (RNA molecules play essential roles in producing proteins and in other cell activities.) Studies suggest that the loss of a particular group of snoRNA genes, known as the SNORD116 cluster, may play a major role in causing the signs and symptoms of Prader-Willi syndrome. However, it is unknown how a missing SNORD116 cluster could contribute to intellectual disability, behavioral problems, and the physical features of the disorder.

In some people with Prader-Willi syndrome, the loss of a gene called OCA2 is associated with unusually fair skin and light-colored hair. The OCA2 gene is located on the segment of chromosome 15 that is often deleted in people with this disorder. However, loss of the OCA2 gene does not cause the other signs and symptoms of Prader-Willi syndrome. The protein produced from this gene helps determine the coloring (pigmentation) of the skin, hair, and eyes.

Researchers are studying other genes on chromosome 15 that may also be related to the major signs and symptoms of this condition.

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