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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 discovered in 1956 by Andrea Prader, Heinrich Willi, Alexis Labhart, and Guido Fanconi of Switzerland.

Babies with Prader-Willi syndrome are born with low muscle tone and a weak sucking reflex. Once the muscles strengthen, however, their insatiable appetite takes over. They eat and eat, never feeling full. As they have a lower metabolism than normal people, they often end up obese if the kitchen isn't locked. This is caused by a misdevelopment of the hypothalamus.

The genes of Prader-Willi syndrome are expressed only on the paternal chromosome. The eighth gene in the segment, whose deletion causes Angelman syndrome, is expressed only on the maternal chromosome. It is thus possible for a woman with Prader-Willi syndrome to pass the mutation to her son, who has Angelman syndrome. This is the first known instance of imprinting in humans.

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