People normally inherit one copy of chromosome 15 from each parent.
Prader- Willi syndrome occurs when the region of the parental chromosome 15 containing certain genes are missing.
Prader Willi is caused by a deletion in the paternal chromosome 15 or by maternal uniparental disomy.
HOW IS IT DIAGNOSED?
A diagnosis of Prader-Willi syndrome (PWS) is usually made by a physician based on symptoms. PWS is shown in infant born with hypotonia (muscle weakness or “floppiness”). The diagnosis is confirmed by a blood test.
physical features of PWS
Poor muscle tone
Distinct facial features -almond shape eyes
failure to thrive-infants have poor sucking reflex due to poor muscle tone
Lack of eye coordination- eyes may not move together they may start to cross or wander to the side.
Generally poor responsiveness- usually tired, having a hard time to wake up or have a weak cry
a father with PWS who has a deletion in chromosome 15 has a 50% chance that he will pass on the affected chromosome to his child which will have Prader-Willi. This is because a mother's genes that has Prader-Willi are normally inactivated so the child will have no active copies of these genes.
Rarely, a genetic change responsible for Prader-Willi syndrome can be inherited. For example, it is possible for a genetic defect that abnormally inactivates genes on the paternal chromosome 15 to be passed from one generation to the next.
If obesity and other symptoms is regulated, victim may have a normal life expectancy. If it isn't regulated then t is shortened
There is no cure for Prader-Willi Syndrome currently.
The treatment of Prader-willi is basically treating the symptoms of the disorder as they arise.
Prader-Willi Syndrome affects an estimated in 1 in 10,000 to 30,000 people worldwide.
http://www.nichd.nih.gov/health/topics/prader-willi/conditioninfo/Pages/faqs.aspx
http://ghr.nlm.nih.gov/condition/prader-willi-syndrome
http://www.med.umich.edu/yourchild/topics/praders.htm