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Prader-Willi syndrome (abbreviated PWS) is a very rare genetic disorder, in which seven genes (or some subset thereof) on chromosome 15 are missing or unexpressed (chromosome 15q partial deletion) on the paternal chromosome. It was first described in 1956 by Andrea Prader, Heinrich Willi, Alexis Labhart, Andrew Ziegler, and Guido Fanconi of Switzerland.[1] The incidence of PWS is between 1 in 12,000 and 1 in 15,000 live births. The distinction of chromosome by parental origin is due to imprinting and PWS has the sister syndrome Angelman syndrome that affects maternally imprinted genes in the region.
It is characterized by polyphagia and food preoccupations which often leads to obesity. Short stature and learning difficulties are also often common.
PWS is characterized by polyphagia and food preoccupations, as well as short stature and learning difficulties.
Traditionally, PWS was diagnosed by clinical presentation. Currently, the syndrome is diagnosed through genetic testing; testing is recommended for newborns with pronounced hypotonia (floppiness). Early diagnosis of PWS allows for early intervention as well as the early prescription of growth hormone. Daily recombinant growth hormone (GH) injections are indicated for children with PWS. GH supports linear growth and increased muscle mass, and may lessen food preoccupation and weight gain.
The mainstay of diagnosis is genetic testing, specifically DNA-based methylation testing to detect the absence of the paternally contributed Prader-Willi syndrome/Angelman syndrome (PWS/AS) region on chromosome 15q11-q13. Such testing detects over 97% of patients. Methylation-specific testing is important to confirm the diagnosis of PWS in all individuals, but especially those who are too young to manifest sufficient features to make the diagnosis on clinical grounds or in those individuals who have atypical findings.
Prader-Willi syndrome is often misdiagnosed as Down syndrome, simply because of the relative frequency of Down syndrome compared to PWS. Also, marked obesity can occur in Down syndrome due to behavioral problems. Adding to the confusion, parents of children who already carry a diagnosis of Prader-Willi syndrome may tell friends, family, and even physicians and nurses that their child has Down syndrome because more people have heard of that condition.
Clinical Features And Signs
Holm et al (1993) describe the following features and signs as pretest indicators of PWS, although not all will be present.
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