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What are some facts about Prader Willi syndrome?

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Prader-Willi syndrome is a genetic condition that causes poor physical growth and feeding difficulties in infancy before progressing to insatiable hunger and obesity throughout childhood and adulthood, as Genetics Home Reference explains. The condition develops when genetic material from chromosome 15 is deleted, deactivated or translocated or if a child inherits multiple copies from one parent. The syndrome may cause wide-ranging developmental and behavioral symptoms, such as intellectual impairment, compulsions, sleep abnormalities, infertility and temper outbursts.

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As infants, people with Prader-Willi syndrome experience lethargy and exhibit weak muscle tone and poor weight gain, as the National Organization for Rare Disorders describes. They typically have a short stature and characteristic facial features such as a downturned mouth, almond-shaped eyes and a long, narrow head. Between ages 4 and 8, compulsive overeating leads to rapid weight gain, and untreated individuals have an exceptionally high risk of morbid obesity, diabetes, high blood pressure and lung complications. The compulsion is so intense that an unsupervised person may consume spoiled or discarded food, and they may also steal money for food.

In about 70 percent of cases, a portion of the paternal chromosome 15 is deleted in every cell and the maternal genes aren't active, according to Genetics Home Reference. Roughly 25 percent of cases are caused by maternal uniparental disomy, in which the mother passes on two copies of chromosome 15.

Another 5 percent occur when a genetic process known as imprinting is defective and incorrectly deactivates certain paternal genes, as the National Organization for Rare Disorders explains. The most rare cause is translocation, in which segments of chromosomes are displaced. This leads to an abnormal arrangement of genetic material.

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