What is Prader-Willi syndrome?
Prader-Willi syndrome (PWS) is a genetic disorder that occurs in approximately one out of every 15,000 births. PWS affects males and females with equal frequency and affects all races and ethnicities. PWS is recognized as the most common genetic cause of life-threatening childhood obesity.
PWS was first described by Swiss doctors Andrea Prader, Alexis Labhart, and Heinrich Willi in 1956 based on the clinical characteristics of nine children they examined. The common characteristics defined in the initial report included small hands and feet, abnormal growth and body composition (small stature, very low lean body mass, and early-onset childhood obesity), hypotonia (weak muscles) at birth, insatiable hunger, extreme obesity, and intellectual disability.
PWS results from an abnormality of chromosome 15, and definitive diagnosis is now based on genetic testing.
This video gives a brief overview of PWS:
What are the symptoms of Prader-Willi syndrome?
The symptoms of Prader-Willi syndrome are likely due to dysfunction of a portion of the brain called the hypothalamus. The hypothalamus is a small endocrine organ at the base of the brain that plays a crucial role in many bodily functions, including regulating hunger and satiety, body temperature, pain, sleep-wake balance, fluid balance, emotions, and fertility. Although hypothalamic dysfunction is believed to lead to the symptoms of PWS, it is not yet clear how the genetic abnormality causes hypothalamic dysfunction.
The symptoms of PWS change over time in individuals with PWS, and a detailed understanding of the nutritional stages of PWS has been published. Overall, there are two general stages of the symptoms associated with PWS:
Infants with PWS are hypotonic or “floppy”, with very low muscle tone. A weak cry and a poor suck reflex are typical. Babies with PWS usually are unable to breastfeed and frequently require tube feeding. These infants may suffer from “failure to thrive” if feeding difficulties are not carefully monitored and treated. As these babies grow older, strength and muscle tone generally improve. Motor milestones are achieved, but are usually delayed. Toddlers typically enter a period where they may begin to gain weight easily, prior to having a heightened interest in food.
Childhood and Beyond
An unregulated appetite and easy weight gain characterize the later stages of PWS. These features most commonly begin between ages 3 and 8 years old, but are variable in onset and intensity. Individuals with PWS lack normal hunger and satiety cues. They usually are not able to control their food intake and will overeat if not closely monitored. Food seeking behaviors are very common. In addition, the metabolic rate of persons with PWS is lower than normal. Left untreated, this combination of problems leads to morbid obesity and its many complications.
In addition to obesity, a variety of other symptoms can be associated with Prader-Willi syndrome. Individuals usually exhibit cognitive challenges, with measured IQs ranging from low normal to moderate intellectual disability. Those with normal IQs usually exhibit learning disabilities. Other issues may include growth hormone deficiency/short stature, small hands and feet, scoliosis, sleep disturbances with excessive daytime sleepiness, high pain threshold, speech apraxia/dyspraxia, and infertility. Behavioral difficulties may include obsessive-compulsive symptoms, skin picking, and difficulty controlling emotions. Adults with PWS are at increased risk for mental illness. PWS is a spectrum disorder and symptoms vary in severity and occurrence among individuals.