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Prader–Willi syndrome (; abbreviated PWS) is a rare genetic disorder in which seven genes (or some subset thereof) on chromosome 15 (q 11–13) are deleted or unexpressed (chromosome 15q partial deletion) on the paternal chromosome. It was first described in 1956 by Andrea Prader (1919–2001), Heinrich Willi (1900–1971), Alexis Labhart (1916–1994), Andrew Ziegler, and Guido Fanconi of Switzerland. Characteristic of PWS is "low muscle tone, short stature, incomplete sexual development, cognitive disabilities, behavior problems, and a chronic feeling of hunger that can lead to excessive eating and life-threatening obesity."〔(【引用サイトリンク】url=http://www.pwsausa.org/faq.htm )〕 The incidence of PWS is between 1 in 25,000 and 1 in 10,000 live births. The paternal origin of the genetic material that is affected in the syndrome is important because the particular region of chromosome 15 involved is subject to parent-of-origin imprinting, meaning that for a number of genes in this region, only one copy of the gene is expressed while the other is silenced through imprinting. For the genes affected in PWS, it is the maternal copy that is usually imprinted (and thus is silenced), while the mutated paternal copy is not functional.〔 "Absence of the paternally inherited copy of these genes, or failure to express them, causes total absence of expression for those genes in the affected individual because the maternal contribution for these genes has been programmed by epigenetic factors to be silenced"〕 This means that while most people have one working and one silenced set of these genes, people with PWS have a non-working set and a silenced set. If the ''maternally'' derived genetic material from the same region is affected instead, the sister Angelman Syndrome is the result. With the recent benefits of early diagnosis and ongoing interventions, the obesity rate among children with Prader–Willi Syndrome has decreased to be similar to the typical population. With behavioural therapy and other treatments, the effects of the syndrome can be reduced. ==Signs and symptoms== There are many signs and symptoms of Prader-Willi Syndrome. The symptoms can range from poor muscle tone during infancy to behavioral problems in early childhood. Some symptoms that are usually found in infants, besides poor muscle tone, would be a lack of eye coordination; some are born with almond-shaped eyes; and due to poor muscle tone the infant may not have a strong sucking reflex. Their cry is weak, and they have difficulty waking up. Another sign of this disease is a thin upper lip. Holm ''et al.'' (1993) describe the following features and signs as pretest indicators of PWS, although not all will be present. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Prader–Willi syndrome」の詳細全文を読む スポンサード リンク
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