Scientists think that the symptoms of PWS may be caused by a problem in a portion of the brain called the hypothalamus. The hypothalamus lies in the base of the brain. When it works normally, it controls hunger or thirst, body temperature, pain, and when it is time to awaken and to sleep.1 Problems with the hypothalamus can affect various body functions and pathways, leading to a variety of symptoms.
Individuals with PWS may have mild to severe symptoms.
An important early symptom of PWS is an infant's inability to suck, which affects the ability to feed. Nearly all infants with PWS need help with feeding. Infants may require feeding support for several months. Without assistance, they will not grow. Nursing systems with one-way valves and manual sucking assistive devices, similar to those used with cleft palate (such as bottles with special nipples for babies who do not have the sucking reflex), often are needed. Occasionally, feeding tubes are required, but generally for no more than the first 6 months after birth. The infants may need fewer calories because of the reduced metabolism associated with PWS and may not demand feeding on their own. Frequent weight checks will help in adjusting the infant's diet to maintain a suitable weight gain.
As the infants grow into toddlers and children, compulsive overeating replaces the need for feeding support. Because the metabolic rate of individuals with PWS is lower than normal, their caloric intake must be restricted to maintain a healthy weight, often to 60% of the caloric requirement of comparably sized children without the syndrome.
Feeding and metabolic symptoms persist into adulthood. Unless individuals with PWS live in environments that limit access to food (such as locked cabinets and a locked refrigerator), they will eat uncontrollably, even food that is rotten or sitting in the garbage. Uncontrollable eating can cause choking, a ruptured esophagus, and blockages in the digestive system. It can also lead to extreme weight gain and morbid obesity. Because of their inability to stop eating, people with PWS are at increased risk for diabetes, trouble breathing during sleep, and other health risks.1 For these reasons, people with PWS need to be monitored by a health care professional their entire lives.
Many physical symptoms of PWS arise from poor regulation of various hormones, including growth hormone, thyroid hormone, and possibly adrenalin. Individuals with PWS grow slowly and experience delays in reaching physical activity milestones (e.g., standing, walking).2
Children with PWS tend to be substantially shorter than other children of similar age. They may have small hands and feet and a curvature of the back, called scoliosis. In addition, they frequently have difficulty making their eyes work together to focus, a condition called strabismus.2,3
Infants with PWS are often born with underdeveloped sex organs, including a small penis and scrotum or a small clitoris and vaginal lips. Most individuals with PWS are infertile.1,2,4
Imbalances in hormone levels may contribute to behavioral and psychiatric problems. Behavioral problems may include temper tantrums, extreme stubbornness, obsessive-compulsive symptoms, picking the skin, and general trouble in controlling emotions. The individual will often repeat questions or statements. Sleep disturbances may include excessive daytime sleepiness and disruptions of sleep. Many individuals with PWS have a high pain threshold.1
The appearance of PWS symptoms occurs in two recognized stages:
Stage 1 (Infancy to age 2 years)
- "Floppiness" and poor muscle tone
- Weak cries and a weak sucking reflex
- Inability to breastfeed, which may require feeding support, such as tube feeding
- Developmental delays
- Small genital organs
Stage 2 (Ages 2 to 8)
- Unable to feel satisfied with normal intake of food
- Inability to control eating, which can lead to overeating if not monitored
- Food-seeking behaviors
- Low metabolism
- Weight gain and obesity
- Daytime sleepiness and sleep problems
- Intellectual disabilities
- Small hands and feet
- Short stature
- Curvature of the spine (scoliosis)
- High pain threshold
- Behavioral problems, including the display of obsessive-compulsive symptoms, picking the skin, and difficulty controlling emotions
- Small genitals, often resulting in infertility in later life
- McCandless, S. E.; Committee on Genetics. (2011). Clinical report-health supervision for children with Prader-Willi syndrome. Pediatrics, 127, 195-204.
- Gunay-Aygun, M., Schwartz, S., Heger, S., O'Riordan, M. A., & Cassidy S. B. (2001). The changing purpose of Prader-Willi syndrome clinical diagnostic criteria and proposed revised criteria. Pediatrics. 108, e92. Retrieved on May 30, 2012, from https://pubmed.ncbi.nlm.nih.gov/11694676/
- Holm, V. A., Cassidy, S. B., Butler, M. G., Hanchett, J. M., Greenswag, L. R., Whitman, B. Y., et al. (1993). Prader-Willi syndrome: consensus diagnostic criteria. Pediatrics, 91, 398-402.
- Cassidy, S.B., & Schwartz S. (2009). Prader-Willi syndrome. NCBI Bookshelf, a Service of the National Library of Medicine, National Institutes of Health. Bookshelf ID: NBK1330.