Related Terms

• Binge eating, chromosome 15, cryptorchidism-dwarfism-subnormal mentality, HHHO, hypogenital dystrophy with diabetic tendency, hypotonia, hypotonia-hypomentia-hypogonadism-obesity syndrome, insulin resistance, Labhart-Willi syndrome, metabolic syndrome, obesity, overweight, Prader-Labhart-Willi Fancone syndrome, PWS, strabismus, translocation, uniparental disomy, Willi-Prader syndrome.

Background

• Prader-Willi syndrome is a rare genetic disorder that causes decreased muscle tone, mild-to-moderate intellectual disability, and an intense appetite during childhood and adulthood. Behavioral problems, such as a quick temper or obsessive-compulsive disorder, are also common.

• Because they often have poor muscle tone at birth, children born with Prader-Willi syndrome may have difficulty feeding until they are about one year old. However, children soon develop insatiable appetites and typically gain weight rapidly. As a result, individuals with this disorder are often overweight or obese. Many of the complications of Prader-Willi syndrome, including diabetes, sleep apnea, high blood pressure, right-sided heart failure, and joint problems, are caused by obesity.

• It is estimated that one out of 10,000-25,000 people worldwide have Prader-Willi syndrome.

• There is no cure for Prader-Willi syndrome. However, many treatments and therapies may help patients cope with the disorder and help prevent complications. Weight control is especially important to prevent complications of obesity.

Risk Factors

• Most cases of Prader-Willi syndrome occur randomly, with no family history of the disease. In rare cases, the disorder may be inherited, or passed down in families. Therefore, people with a family history of Prader-Willi syndrome have an increased risk of having the disorder.

Causes

• General: People with Prader-Willi syndrome are born with fewer-than-normal functional genes inside a specific region of chromosome 15. Normally, humans inherit one copy of chromosome 15 from each parent. Some genes in chromosome 15 are active only in the copy that is inherited from the father, which is the paternal copy. Prader-Willi syndrome occurs when a piece of paternal chromosome 15 that contains these genes is missing.

• Researchers are still trying to identify the specific genes on chromosome 15 that lead to this disorder. So far, researchers have determined that a deletion of the oculocutaneous albinism type 2 (OCA2) gene on chromosome 15 is associated with unusually fair skin and light-colored hair in some people with Prader-Willi syndrome. Normally, this gene provides instructions that tell the body how to produce P protein, which helps determine the coloring of the skin, hair, and eyes.

• Random occurrence: More than 90% of Prader-Willi syndrome cases are not inherited. Instead, the mutation occurs randomly during the development of the sperm cells, egg cells, or embryo. This means most people with Prader-Willi syndrome do not have a family history of the disorder.

• In such instances, about 70% of cases occur when a piece of the father's chromosome 15 (the paternal chromosome) is deleted in each cell. In about 25% of these random cases, Prader-Willi syndrome occurs when a person receives two copies of chromosome 15 from his or her mother instead of just one, and no copy of chromosome 15 from his or her father. When a person inherits two copies from the mother, it is called uniparental disomy.

• Inheritance: In two percent of cases or fewer, Prader-Willi syndrome may be inherited. This occurs when a chromosome is rearranged, or translocated, or when a mutation or other defect abnormally inactivates genes on paternal chromosome 15. In such cases, the parents do not have Prader-Willi syndrome, even though they passed on the condition to their children.

Signs and Symptoms

• General: Signs and symptoms of Prader-Willi syndrome are often apparent shortly after birth. The condition is typically diagnosed in early childhood.

• Failure to thrive: Because infants often have poor muscle tone at birth, they may have poor sucking reflexes during the first year of life. As a result, infants may have difficulty feeding and may gain weight more slowly than healthy infants. If not properly treated, infants may become malnourished.

• Poor muscle tone: Infants with Prader-Willi syndrome typically have poor muscle tone at birth. This may lead to difficulty feeding during infancy. In addition, having less muscle tone means they are able to burn fewer calories than their healthy peers during childhood, making them more susceptible to obesity.

• Distinctive facial features: Distinctive facial features, including almond-shaped eyes, narrow temples, a thin upper lip, a downturned mouth, full cheeks, and strabismus (crossed eyes), may be apparent at birth.

• Voracious appetite: After the first year of life, individuals with Prader-Willi syndrome typically have voracious appetites, because the hypothalamus, the part of the brain that controls feelings fullness, does not work properly. As a result, these individuals constantly crave food and overeat, and it is common for them to become overweight or obese.

• Delayed motor development: Toddlers with Prader-Willi syndrome often reach motor milestones later than their peers who do not have the condition. For instance, most healthy children are able to sit up by 12 months and able to walk by 24 months. It may take children with Prader-Willi syndrome longer to achieve these and similar milestones.

• Underdeveloped sex organs: Children with the disorder typically have underdeveloped sex organs. This condition, called hypogonadism, occurs when the testes in males and the ovaries in females produce few or no sex hormones. Testosterone is considered the male hormone, while estrogen and progesterone are considered the female hormones. Adolescents with Prader-Willi syndrome may develop pubic and underarm hair, but other secondary sexual characteristics, such as testicular development in males and breast development in females, may be delayed or not occur at all. Most people with Prader-Willi syndrome are infertile.

• Intellectual disability: People with Prader-Willi syndrome may have mild-to-moderate intellectual or learning disabilities. Intellectual disability is a condition that causes significantly impaired cognitive functioning from birth or early infancy and ultimately limits the individual's ability to perform normal daily activities. Learning disabilities are disorders that occur when patients have difficulty interpreting or processing what they see or hear. There is frequently a gap between the patient's intelligence and his or her performance in school, work, or other areas of life.

• Behavioral problems: People with Prader-Willi syndrome may exhibit behavioral problems if they are denied food. For instance, some children may throw temper tantrums and become very angry or stubborn if parents limit the amount of food they can eat. Some people may develop obsessive-compulsive disorder (OCD) or unusual food-seeking behavior, such as eating food out of the garbage, sneaking food, or hiding their eating habits from others.

• Obesity: Because people with Prader-Willi syndrome have voracious appetites and less muscle to burn calories, they often become overweight or obese. Obesity is usually defined as being 20-30% above the normal body weight for someone of the same age, sex, and height. Morbid obesity is usually defined as being 50-100% above the normal body weight for someone of the same age, sex, and height.

• Other symptoms: People with Prader-Willi syndrome may also have small hands and feet, nearsightedness, loss of skin pigmentation, stretch marks, or high pain tolerances.

Diagnosis

• Clinical guidelines: Clinical diagnostic guidelines for Prader-Willi syndrome have been established, although genetic testing is considered the standard diagnostic tool.

• Major and minor criteria can be used to diagnose Prader-Willi syndrome. Each major criterion observed in a patient counts as one point, while each minor criterion counts as 0.5 points. Prader-Willi syndrome is suspected in children younger than three years of age with a score of at least five and in children three years and older with a score of at least eight, and with four points from major criteria.

• Major criteria include characteristic facial features, feeding problems or failure to thrive during infancy, developmental delay, hypogonadism, a type of low muscle tone in infants called infantile central hypotonia, and rapid weight gain between one and six years of age.

• Minor criteria include decreased fetal movement and lethargy during infancy, eyes that turn inward or nearsightedness, lack of skin pigment, narrow hands with straight ulnar border, short stature compared with family members, and characteristic behavioral problems.

• Genetic testing: Genetic testing is highly accurate and can accurately detect Prader-Willi syndrome nearly 100% of the time. If there is a family history of Prader-Willi syndrome, prenatal genetic testing may be suggested. Depending on the specific type of prenatal test performed, a doctor takes either a sample of the mother's amniotic fluid or chorionic villi tissue from the placenta. Amniocentesis is typically performed between the 15th and 17th weeks of gestation, but occasionally as early as the 14th or as late as the 20th week. Chorionic villus sampling is normally performed in the first trimester in a hospital. The sample is then analyzed for the presence of characteristic mutations in chromosome 15.

• There are risks associated with prenatal testing, including miscarriage. Therefore, patients should talk to their doctor about the potential health risks and benefits before making any health-related decisions.

Complications

• General: Many of the major complications of Prader-Willi syndrome, including bone and joint problems, cor pulmonale (a type of heart disease that causes lung problems), diabetes, and heart disease, are caused by morbid obesity. Other complications, including infertility and osteoporosis, are caused by underdeveloped sex organs, a condition called hypogonadism.

• Bone and joint problems: People who are overweight or obese have an increased risk of developing osteoarthritis, a common degenerative joint disease. This is because being overweight increases the strain put on the weight-bearing joints, such as the knees and ankles. As a result, cartilage in the joints begins to break down.

• Diabetes: Overweight or obese people with Prader-Willi syndrome have an increased risk of developing type 2 diabetes. When type 2 diabetes is diagnosed, the pancreas is usually producing enough insulin, but for unknown reasons, the body cannot use the insulin effectively. This condition is known as insulin resistance. After several years of making extra insulin to compensate for the body's inefficient use, insulin production is decreased. As a result, people with type 2 diabetes have too much sugar in their bloodstream.

• High blood pressure: Overweight or obese people have an increased risk of developing high blood pressure. This is because the extra fat tissue, like any tissue in the body, requires oxygen from the blood. Therefore, the circulatory system is strained and the heart rate increases as it tries to supply a larger-than-normal body with enough oxygenated blood. In addition, obesity tends to increase the amount of insulin in the blood. High levels of insulin cause the body to retain sodium and water, which increases blood volume.

• High cholesterol: Individuals who are overweight also have an increased risk of developing high cholesterol, which may also lead to atherosclerosis (hardening of the arteries) or coronary artery disease (CAD).

• High cholesterol levels can cause plaque deposits to form in the arteries. Plaque is composed of cholesterol, other fatty substances, fibrous tissue, and calcium. When plaque builds up in the arteries, it causes atherosclerosis or CAD. Atherosclerosis can lead to plaque ruptures and blockages in the arteries. If the blood supply to the heart is blocked, a heart attack may occur. If blood supply to the brain is blocked, a stroke may occur.

• Cor pulmonale: Overweight or obese people with Prader-Willi syndrome have an increased risk of experiencing cor pulmonale, a type of right-sided heart failure. The right side of the heart receives blood from the body and pumps it to the lungs. Cor pulmonale occurs when the heart has difficulty pumping blood to the lungs. Cor pulmonale may occur if the patient has lung problems, such as chronic obstructive pulmonary disease (COPD). Symptoms may include chronic coughing, wheezing, weakness, shortness of breath, and discomfort or fluid buildup in the chest. Cor pulmonale may lead to complete heart failure.

• Sleep apnea: People with Prader-Willi syndrome who are overweight or obese have an increased risk of developing sleep apnea, a serious condition that occurs when the individual stops breathing for short periods of time during sleep. In obese patients, sleep apnea typically occurs when excess fat in the upper airway obstructs breathing. Because sleep apnea causes individuals to wake up frequently throughout the night, patients are often drowsy during the day. In addition, sudden drops in blood oxygen levels during sleep put strain on the cardiovascular system and increase blood pressure.

• Infertility: Most people with Prader-Willi syndrome are unable to have children because they have low levels of reproductive hormones. However, there have been a few reports of women with Prader-Willi syndrome who became pregnant.

• Osteoporosis: Hypogonadism may lead to osteoporosis, a condition that causes the bones to become weak and brittle. This is because testosterone and estrogen are essential for healthy bones. Estrogen increases bone density by helping to block bone resorption, and low testosterone levels have been linked to thinning bones. Therefore, osteoporosis may develop as early as childhood or adolescence. Because osteoporosis causes the bones to become porous and less dense, people are more likely to suffer a fracture with an injury, for example, a hip broken in a fall. Sometimes spinal bones can break without any traumatic injury because the bones are very weak.

• Some evidence suggests that osteoporosis may develop in obese patients because fat cells infiltrate the bone marrow, leading to weak bones. In addition, it has been shown that individuals who live sedentary lifestyles have an increased risk of developing osteoporosis.

Treatment

• General: Children with Prader-Willi syndrome require lifelong care, but with proper management, these children can expect to lead full lives. Although there is no cure for Prader-Willi syndrome, many treatments and therapies may help patients cope with the disorder and help prevent complications. Weight control is especially important to prevent complications of obesity, such as heart disease and type 2 diabetes.

• Encouraging feeding during infancy: Many infants with Prader-Willi syndrome have difficulty feeding because they have decreased muscle tone. Pediatricians may recommend a high-calorie formula in order to help infants with the disorder gain weight.

• Healthy, low-calorie diet: A healthy diet is important to prevent obesity. Individuals with Prader-Willi syndrome three years of age and older are encouraged to follow a strict low-calorie diet. Patients with Prader-Willi syndrome require fewer calories than people who do not have the disorder, because they have less muscle mass and tend to burn fewer calories.

• In general, healthcare professionals suggest that all individuals drink adequate water daily and eat a diet rich in fruits, vegetables, and whole grains. Some individuals may find it helpful to eat frequent small meals throughout the day to keep the body's energy and metabolism increased. Foods and drinks that contain a lot of sugar and little or no nutritional value should be consumed in moderation. This means individuals should limit their intake of foods and drinks such as coffee, alcohol, soft drinks, fruit juices high in sugar, processed foods, white sugar, white flour, red meat, and animal fats.

• A healthcare provider may recommend a consultation with a registered dietitian to help parents and caregivers plan meals and an eating plan that are appropriate for the patient. He or she can also determine whether a patient needs supplemental vitamins and minerals in order to ensure balanced nutrition. It is important for the patient to understand the negative impact that poor eating habits have on the body.

• Most experts recommend that parents and caregivers store food out of their children's reach. They even suggest locking pantries, refrigerators, and cupboards, because people with Prader-Willi syndrome often exhibit extreme food-seeking behavior and, without limitations, they may eat uncontrollably.

• Exercise programs: In general, patients who are overweight or obese are encouraged to exercise. Research shows that regular exercise can help individuals live longer, healthier lives. Exercise may help prevent illnesses such as heart disease, stroke, diabetes, and cancer.

• In general, overweight patients should participate in 45-60 minutes of moderate exercise (e.g., brisk walking or jogging) each day in order to prevent obesity. Formerly obese patients are encouraged to participate in 60-90 minutes of moderate exercise each day and eat a healthy, well-balanced diet in order to prevent regaining weight.

• Not everyone is able to perform intense types of exercise, such as tennis or running. Individuals who are overweight or obese may have serious health conditions that limit the type or amount of exercise they can perform. Therefore, patients should talk to their healthcare provider before starting a new exercise plan. A healthcare provider can work with a patient to design an individualized and safe exercise program.

• Occupational therapy: Patients with Prader-Willi syndrome may benefit from occupational therapy. During sessions a therapist helps the child learn skills to help him or her perform basic daily tasks, such as eating, dressing, and communicating with others. Parents and caregivers can ask their child's pediatrician for recommended therapists.

• Education: The Individuals with Disabilities Education Act requires that all children with disabilities, including those with Prader-Willi syndrome who have intellectual disabilities, have access to free and appropriate education tailored to their specific needs. According to the law, staff of the patient's school must consult with the patient's parents or caregivers to design and write an individualized education plan. Once all parties agree to the plan, the educational program should be started. The school faculty must document the child's progress in order to ensure that the child's needs are being met.

• Educational programs vary among patients. According to the Free Appropriate Public Education (FAPE) guidelines, schools are required to teach students who have disabilities in the least restrictive environment possible. This means that a student with a disability should have the opportunity to be educated with his or her nondisabled peers to the greatest extent possible. The idea is that nondisabled students will help the disabled student learn appropriate behavioral, social, and language skills. Some patients, then, are educated in mainstream classrooms. Others attend public schools but take special education classes. Others attend specialized schools designed to teach children with disabilities.

• Speech-language therapy: Patients with Prader-Willi syndrome and intellectual disabilities may benefit from speech-language therapy, because such individuals often develop communication skills slower than normal. During speech-language therapy, a qualified speech-language professional works with the patient on a one-to-one basis, in a small group, or directly in a classroom to help the patient improve speech, language, and communication skills. Programs are tailored to the patient's individual needs.

• Speech pathologists use a variety of exercises to improve the patient's communication skills. Exercises typically start off simple and become more complex as therapy continues. For instance, the therapist may ask the patient to name objects, tell stories, or explain the purpose of an object.

• On average, patients receive five or more hours of therapy per week for three months to several years. Doctors typically recommend that treatment begin early to ensure the best possible outcome for the child.

• Physical therapy: Physical therapy may help patients improve their physical strength and motor coordination. For example, a physical therapist may be able to help infants with Prader-Willi syndrome and poor muscle tone learn how to roll over, sit up, and walk. Because adults generally have less muscle than their peers without Prader-Willi syndrome, they may also benefit from physical therapy. A variety of techniques, including exercises, stretches, traction, electrical stimulation, and massage, are used during physical therapy sessions.

• Eye treatments: Some children with Prader-Willi syndrome have strabismus (crossed eyes). An ophthalmologist (a doctor who specializes in disorders of the eyes) may prescribe glasses, eye exercises, or a patch placed over the child's normal eye to help improve strabismus and vision.

• Human growth hormone: It has been suggested that injections with human growth hormone may be beneficial in children with Prader-Willi syndrome. Because human growth hormone stimulates the growth of bones and muscle, researchers suggest that it may help increase growth and decrease body fat in children with this disorder. Some doctors recommend starting growth hormone therapy immediately after diagnosis, while others recommend waiting until the child starts to fall off the growth curve. However, the long-term effects of human growth hormone are unknown.

• Hormone therapy with sex hormones: During early childhood, some individuals with Prader-Willi syndrome may receive hormone replacement therapy in order to make up for the low or nonexistent levels of testosterone in males and estrogen and progesterone in females. This therapy may help reduce the risk of developing osteoporosis.

Integrative Therapies

• Currently there is a lack of scientific evidence on the use of integrative therapies for the treatment or prevention of Prader-Willi syndrome.

Prevention

• General: There is currently no known method for preventing Prader-Willi syndrome. Most cases occur randomly and are not inherited.

• Genetic testing and counseling: Individuals who have Prader-Willi syndrome may meet with a genetic counselor to discuss the risks of having children with the disease. However, most people with the disorder are unable to have children. Genetic counselors can explain the options and the associated risks of various tests, including preimplantation genetic diagnosis (PGD), amniocentesis, and chorionic villus sampling (CVS).

• Preventing complications of obesity: Individuals who are overweight or obese should be aware of the health risks associated with these conditions, including high blood pressure, high cholesterol, heart disease, stroke, and diabetes. In order to prevent these complications, people with Prader-Willi syndrome are encouraged to make healthy lifestyle decisions that include eating a well-balanced diet and exercising regularly.

• Regular exercise can help individuals maintain a healthy weight. It has also been shown to control diabetes, reduce stress, and reduce the risk of heart disease and stroke. Thirty minutes daily of exercise is normally recommended. Patients or their caregivers should talk to their healthcare providers before starting new exercise programs.

• Exercise may also help prevent osteoporosis. Weight-bearing aerobic activities, involving the bones supporting body weight, have been shown to have a positive effect in maintaining and increasing bone mass and preventing osteoporosis. These activities include weight lifting, walking, jogging, hiking, stair-climbing, step aerobics, dancing, racquet sports, and other activities that require muscles to work against gravity. Individuals who live a sedentary lifestyle have weaker bones and are at higher risk of sustaining fractures.

• Eating a healthful and well-balanced diet is essential to maintaining a healthy weight. According to the U.S. Department of Agriculture (USDA), a healthy diet should include five or more daily servings of fruits and vegetables, foods rich in soluble fiber (such as oatmeal and beans), foods rich in calcium (such as dairy products and spinach), soy products (such as tempeh, miso, tofu, and soy milk), and foods rich in omega-3 fatty acids, such as cold-water fish (e.g., salmon, mackerel, and tuna), English walnuts, soybean oil, and olive oil.

Author Information

• This information has been edited and peer-reviewed by contributors to the Natural Standard Research Collaboration (www.naturalstandard.com).

Bibliography

Natural Standard developed the above evidence-based information based on a thorough systematic review of the available scientific articles. For comprehensive information about alternative and complementary therapies on the professional level, go to www.naturalstandard.com. Selected references are listed below.

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