Medical » Guidelines for Medical Professionals
(Reference: Management of Prader-Willi Syndrome Third edition, edited by Merlin G. Butler, Phillip D.K. Lee, Barbara Y. Whitman. Published by Springer 2006
Prader-Willi Syndrome is a recognisable pattern of altered growth and development. While the etiology and pathogenesis remain unclear, it is beginning to yield to the application of molecular-genetic technology. Affected persons face life as potentially overweight, short, sexually immature, developmentally delayed individuals with poor gross motor skills. Usually at least mildly intellectually delayed, stubborn, egocentric and emotionally labile, they rarely develop the ability to cope independently with their insatiable hunger and require environmental restrictions to prevent life-threatening obesity.
Although PWS is not a common disorder, it is no longer considered rare. Estimates of the incidence vary between 1:10,000 and 1:25,000 [the NZ PWS Association knows of approximately 100 persons in NZ]
This unique disorder manifests abnormalities of growth, learning, and physical development that may provide clues to understanding many larger issues such as eating disorders and weight control, the neurophysiology of behaviour, patterns of genetic inheritance and the genetic control of morphogenesis.
see also Genetic Diagnosis
Approximately 70% of patients with the clinical presentation of PWS have been shown to have a deletion of the proximal part of the long arm of chromosome 15, described as 15Q11,q13. The remaining 30% have an apparently normal 15th chromosome. Molecular studies have shown that for patients with PWS who have deletions these deletions are from the paternally derived chromosome 15. In individuals with nondeletion, they have been shown to have two maternally derived chromosome 15.
Although the vast majority of cases occur as sporadic events in families, several familial recurrences have been documented around the world. Genetically, these show an imprinting mutation.
"Many clinical features in PWS may be subtle or non-specific while other features are more characteristic for the disorder. The primary features of PWS include infantile hypotonia, feeding difficulties, mental deficiency, hypogonadism, behaviour problems, hyperphagia and early childhood onset of obesity, small hands and feet, endocrine disturbances including recently identified growth hormone deficiency and a characteristic facial appearance (small upturned nose, narrow bifrontal diameter, dolichocephaly, down-turned corners of the mouth, sticky saliva, almond-shaped eyes, and strabismus)" (ref p.7 Ch.1)
For a clinical diagnosis, the following is a consensus diagnostic criteria for Prader-Willi Syndrome. Authors: Holm et al. Published 1993, Pediatrics 91, 398.
Major criteria are weighted at one point each.
Minor criteria are weighted at one-half point.
Children 3 years of age or younger: five points are required for diagnosis, four of which should come from the major group.
Children 3 years of age to adulthood: total score of eight is necessary for the diagnosis. Major criteria must comprise five or more points of the total score.