Prader-Willi syndrome (PWS) is a complex genetic disorder impacting virtually every aspect of an affected individual's life. It is caused by the absence of expression of paternally inherited imprinted genes on chromosome 15q11-q13. This multisystem neurodevelopmental disorder affects approximately 1 in 25,000 live births. Individuals with PWS have brain abnormalities, including dysfunction of the hypothalamus, which contributes to abnormal appetite and satiety control, atypical body temperature and pain regulation, self-mutilatory behaviors (e.g., skin picking), and aberrant sleep cycle.
Early diagnosis and treatment can improve the quality of life for people with Prader-Willi syndrome. A diagnosis can be made through genetic testing nearly all the time, typically after healthcare professionals suspect PWS based on symptoms.
Understanding the Nutritional Phases of Prader-Willi Syndrome
Until recently, it was thought that there were two nutritional phases in PWS: Phase 1 - hypotonia and failure to thrive, and Phase 2 - obesity and hyperphagia. However, it is now recognized that there are several nutritional phases in this syndrome, beginning in utero, with weight and length restriction in affected babies (nutritional Phase 0).
Nutritional Phase 0: Characterized by low birth weight and length, with decreased fetal movements during intrauterine life.
Nutritional Phase 1a: After birth, individuals with PWS have a decreased ability to suckle, as well as lack of desire to eat, which typically necessitates the use of a nasogastric or gastric tube to provide adequate nutrition to the infant (up to about the first 3 months of life). PWS newborn is hypotonic, manifests feeding and suckling deficits.
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Nutritional Phase 1b: Between the ages of 3-12 months, the infant begins to exhibit more typical appetite and satiety signals and will eat normally (up to 12-18 months). The feeding improves, and the infants begin to exhibit normal appetite and growth.
Nutritional Phase 2a: Between 18 months - 3 years of age children with PWS can begin to exhibit excessive weight gain, even without a change in food intake or interest in food.
Nutritional Phase 2b: Around age 4-5 years of age, food begins to have an increased significance for these children, and they begin to ask a lot of food-related questions. Interestingly, they are still able to express satiety in this phase, and will push away food they do not like or even leave some food on their plates.
Nutritional Phase 3: The onset of nutritional Phase 3, which is the classically described appetite phase associated with PWS (constant hunger and lack of satiety), typically occurs sometime after age 8 years. Individuals with PWS display aggressive food seeking, and report that they are constantly looking for opportunities to obtain food. Parents report that their children with PWS will sometimes sneak food and hide or hoard it to eat at a later time, will eat non-edible items, steal food from stores or other people, or will steal money to buy food. One of the most dangerous behaviors that can occur in nutritional phase 3 is elopement from the home to get to food (convenience stores, fast-food restaurants, dumpsters, or neighbors’ homes).
The Critical Role of Dietary Management
Dietary management is important to prevent severe obesity in individuals with Prader‐Willi syndrome (PWS). Hyperphagia, generally recognized as a relentless hunger with lack of satiety, even after consuming a significant amount of calories. Without aggressive environmental food restriction and control, individuals with PWS develop severe obesity, with all of its well-known associated morbidities. Once hyperphagia begins, the focus on food becomes constant and almost impossible to redirect, negatively impacting education, personal interactions, relationships, occupational performance, and quality of life.
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The prevalence of obesity in individuals with PWS varies by age groups, although it has been shown to have a prevalence of 40% in children and adolescents. As individuals with PWS enter adulthood, the prevalence of obesity increases to 82% - 98%, depending on the study group. It is well accepted that once excessive weight gain and hyperphagia begin, caloric intake must be significantly restricted to prevent obesity. However, experienced researchers and clinicians recognize that significant calorie restriction subsequently increases the hunger drive and behavioural problems even more.
Key Strategies for Dietary Control
Strict Meal Plan: To keep from becoming overweight, your child needs a low-calorie diet. Structure mealtimes and the types of food served at meals to create routines and help your child learn expectations.
Portion Control: Use small dishes to serve meals. Portion sizes must be controlled based on the level of weight control and exercise for the individual. We typically recommend using the size of the individual’s fist as a starting point for measurement of portion sizes for complex carbohydrates and protein, and advise limiting healthy fats and fruit portions to what will fit flat in the palm of the individual. We typically do not put a portion size limit on cooked, non-starchy vegetables, and advise that they should fill half of the plate, as is generally recommended with the Mediterranean diet. Basing the portions on the individual’s own palm/fist allows for individualization of the amounts for each person as we are beginning this diet.
Environmental Control: Store food out of your child's reach. Installing locks on all cabinets and pantries, removing access to money and consistent supervision will help to manage their expectations. Don't buy high-calorie snacks.
Consistency and Routine: Removing uncertainty helps children to relax and think less about food, while managing expectations about unplanned extras reduces stress. Create a visual schedule your child can reference, complete with detailed information about meal times and ingredients. Offer verbal reminders of upcoming meals and use them as incentives for good behavior. Just be careful not to frame food as a punishment or reward.
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Address Food Security: When children feel food secure, they have no doubt about the availability or contents of their next meal and no hope for unsanctioned supplementation.
Nutritional Considerations and Macronutrient Balance
People with PWS require very few calories, which is why it’s so easy to overestimate caloric needs. As important as it is to manage the amount of fuel your child consumes, calories are only part of a larger picture. Macronutrients - protein, fat, and carbohydrates - must also be carefully controlled to ensure a balanced diet. An adequate clinical evaluation including nutritional and biochemical parameters should be performed to tailor the best therapeutic strategy. Both lifestyle and pharmacological interventions may represent useful strategies to prevent the high rate of morbidity and mortality related to PWS.
It is well established that individuals with PWS have significant weight gain if they consume the Recommended Daily Allowance (RDA) of calories for their age, gender, and height. This weight gain propensity is due to the fact that those with PWS have significantly lower energy expenditure, including total energy expenditure (TEE), resting energy expenditure (REE), activity energy expenditure (AEE), sleeping energy expenditure (SEE), and diet-induced thermogenesis (DIT).
The Mediterranean Diet Approach
Upon review of all of the available evidence, it seems that the best diet for adolescents with PWS is most similar to the Mediterranean diet. The nutritional profile of the Mediterranean diet is largely plant-based, rich in complex carbohydrates, vegetables, fruits, legumes and nuts, in addition to abundant fish intake (including oily fish). The Mediterranean diet encourages moderate consumption of animal-derived proteins, including eggs, poultry, and dairy products and low consumption of red meat, processed meats and sweets. Moreover, the Mediterranean diet is a healthy diet for everyone, so if the whole family eats the same foods, there is improved adherence for the individual with PWS over the long term.
A Mediterranean-type diet composition consisting of higher-fiber carbohydrates, dairy, healthy fats, and protein may limit the need for significant calorie restriction by providing the fodder for a more healthy gut microbiome, in addition to appropriate energy sources for growth and exercise and improvement of muscle mass.
Addressing Potential Nutritional Deficiencies
An additional issue with calorie-restricted diet in adolescents with PWS is nutritional deficiencies that can occur when calories are restricted. Most low-calorie diets are relatively high in carbohydrates (65% carbohydrate, 15% fat, and 20% protein), and have a relatively high percentage of deficiencies in calcium, vitamin D, and iron. Because of these issues, some groups have studied the effects of a carbohydrate-restricted diet for weight control in adolescents with PWS (15% carbohydrates, 65% fat, and 20% protein). This diet, while effective, at least in the short term, for improved glycemic and weight control, is associated with deficiencies in vitamin D, calcium, and fiber.
Fiber, vitamin D, calcium, and potassium intake were below recommendations in 50% or more in both groups. The inclusion of supplement intake lowered the proportion below recommendations, except for fiber and potassium.
Non-Nutritive Sweeteners: A Word of Caution
Another area of controversy in recommended diet regimens for individuals with PWS is the consumption of non-nutritive sweeteners to replace natural sugars. Individuals with PWS do not like to drink plain water, and therefore are at risk for dehydration and worsened constipation. They will drink sweetened or flavored beverages easily, so most families introduce sugar-substitutes in drinks in order to prevent dehydration in the child/adolescent.
Even artificial sweeteners stimulate the same reward centers in the brain and impact metabolic signals. So while they don’t contain the same amount of calories, they still trigger cravings and food-seeking behaviors. Help your child to view sweet foods as occasional treats, rather than staples in their meal plans.
The Importance of Physical Activity
Physical activity plays a pivotal role in the energy balance in patients with PWS. Studies of exercise performance in individuals with PS have demonstrated impaired stamina and exercise tolerance, decreased cardiorespiratory (maximal oxygen consumption, heart rate recovery after exercise), and abnormally low hormonal responses to exercise. If caregivers are able to get individuals with PWS to engage in consistent aerobic exercise over several months, body composition and body mass index will improve, as will their physical performance. Exercise is crucial following discharge from a PWS program. While movement alone is not enough to combat the effects of an unhealthy diet, it offers a crucial complement to healthy eating habits. When it comes to exercise, there’s no wrong answer.
Components of success for continuing participation in exercise include: clear communication with no ambiguity; provider willingness to adapt when necessary, so as to avoid a temper tantrum or task avoidance; and encouragement for continuation of the exercise routine by eliciting the individual’s input into the types of exercise and goals of the exercise program.
Medical and Therapeutic Interventions
Human Growth Hormone (HGH) Treatment
HGH treatment helps infants and children with Prader-Willi syndrome grow. It also makes muscle tone better and lowers body fat. HGH also may be used in adults. To prevent the onset of obesity and to improve psychomotor development, it is advisable to start GH therapy as soon as possible, between 3 and 6 months of age, monitoring the glucose profile due to the diabetogenic effect of the GH, and the risk of OSA by polysomnography.
Sex Hormone Treatment
Your endocrinologist may suggest that your child take hormone replacement therapy - testosterone for males or estrogen and progesterone for females - because of low levels of sex hormones. Hormone replacement therapy usually starts when your child reaches the usual age for puberty. It can lower the risk of bone thinning, also known as osteoporosis.
Other Therapies
Your child likely will benefit from a range of therapies. These include physical therapy to make movement skills and strength better, speech therapy to make verbal skills better, and occupational therapy to learn everyday skills. Developmental therapy to learn age-appropriate behaviors, social skills and interpersonal skills also may help.
Addressing Behavioral and Mental Health
You may need to create schedules for your child and set strict limits on access to food and how much food is eaten. It's important to be clear on what you expect in terms of your child's behavior. A mental health professional, such as a psychologist or a psychiatrist, may help with mental health problems, such as obsessive-compulsive behaviors, skin picking, anxiety or a mood condition.
Coping and Support
Having a child with Prader-Willi syndrome is challenging and can take a lot of patience. Talk to a mental health professional. Join a support group. Some people find it helpful to talk with others who share similar experiences. Ask your healthcare provider about family support groups in your area. Seek other sources of support. Ask about sources of short-term care and ask for support from family and friends.
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