PWS affects approximately 1 in 10,000 to 1 in 25,000 newborns. There are more than 400,000 people who live with PWS around the world. It is traditionally characterized by hypotonia, short stature, hyperphagia, obesity, behavioral issues (specifically OCD-like behaviors), small hands and feet, hypogonadism, and mild mental retardation. However, with early diagnosis and early treatment (such as with growth hormone therapy), the prognosis for persons with PWS is beginning to change. Like autism, PWS is a spectrum disorder and so symptoms can range from mild to severe, and may change throughout the person's lifetime. Various organ systems are affected.
Traditionally, Prader-Willi Syndrome was diagnosed by clinical presentation. Currently, the syndrome is diagnosed through genetic testing; testing is recommended for newborns with pronounced hypotonia. 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. Because PWS infants have a higher rate of difficulties at birth (including breech delivery and respiratory delay) birth-related injuries and oxygen deprivation may complicate the genetic handicaps, resulting in atypical PWS.
Differential diagnosis
Prader–Willi syndrome is often misdiagnosed as a variety of other syndromes due to many in the medical community's unfamiliarity with PWS. Sometimes it is 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.[citation needed] It is thought that 75% of those with PWS are undiagnosed.