Author: Dr Delwyn Dyall-Smith, Dermatologist, Wagga Wagga, NSW, Australia. Editor-in-Chief: A/Prof Amanda Oakley, Dermatologist, Hamilton, New Zealand. January 2018.
Prader-Willi syndrome is the commonest genetic cause of obesity. It was first described in 1887 by Langdon-Down, 70 years before Prader et al in 1956.
It is also known as Prader-Labhart-Willi syndrome.
* ©Photographic Archive Museo Nacional del Prado. Eugenia Martínez Vallejo is believed to have suffered from Prader-Willi syndrome (ca 1680).
The frequency of Prader-Willi syndrome is reported to be approximately 1 in 25,000 live births, but is likely to be more common due to a failure to diagnose the condition early.
Prader-Willi syndrome has autosomal dominant inheritance, affecting males and females of all races. However, most cases are sporadic.
Prader-Willi syndrome results from the lack of expression of the PWS critical region of chromosome 15. The PWS genes are normally expressed only on the chromosome inherited from the father, and the copy inherited from the mother is switched off.
Three mechanisms are involved.
Angelman syndrome is a clinically distinct disorder due to a maternally derived imprinting defect mapped to the same chromosome as Prader-Willi syndrome.
*Image courtesy Genetics 4 Medics
Clinical features depend on age.
Skin picking is very common and is the most typical cutaneous feature of Prader-Willi syndrome. Lesions are present at all stages of evolution. Signs include scratch marks, bleeding, bacterial skin infection, scabs, scarring, secondary milia — especially on the backs of the hands and forearms.
Other cutaneous features may include:
Clinical diagnostic criteria may be used to diagnose Prader-Willi syndrome.
Genetic studies are the most accurate way to diagnose Prader-Willi syndrome. They should be considered in any floppy newborn baby requiring tube feeding. All three mechanisms for the syndrome should be looked for sequentially, starting with the paternal deletion.
X-rays should be undertaken during childhood to identify skeletal problems, as these can be masked by obesity.
In adult life, dermatologic problems requiring treatment are a major health issue, with erysipelas being a common reason for hospital admission.
Medical complications of Prader-Willi syndrome include:
Differential diagnosis of Prader-Willi syndrome includes other causes of obesity and failure to thrive in infancy and childhood.
Deletion 6q16 syndrome is a Prader-Willi-like syndrome due to proximal deletions of the long arm of chromosome 6. Its main features are:
Genetic counselling is recommended for future pregnancies and family members. Special care may be needed for general anaesthesia. Treatments deal with medical and surgical complications/associations as they arise and are related to age.
Hospital admissions may be required for:
Hospital admission may be required for:
Medications used by adults with Prader-Willi syndrome include psychotropics, laxatives, skin products, and treatments for diabetes.
Respiratory infections are the major health issue in older adults.
Cassidy SB, Dykens E, Williams CA. Prader-Willi and Angelman syndromes: sister imprinted disorders. Am J Med Genet. 2000 Summer;97(2):136-46. Review. PubMed PMID: 11180221. PubMed.
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