Prader-Willi (PRAH-dur VIL-e) syndrome is a rare genetic disorder that results in a number of physical, mental and behavioral problems. A key feature of Prader-Willi syndrome is a constant sense of hunger that usually begins at about 2 years of age.

People with Prader-Willi syndrome want to eat constantly because they never feel full (hyperphagia), and they usually have trouble controlling their weight. Many complications of Prader-Willi syndrome are due to obesity.

Best managed by a team approach, various specialists can work with you to manage symptoms of this complex disorder, reduce the risk of developing complications and improve the quality of life for your loved one with Prader-Willi syndrome.

Signs and symptoms of Prader-Willi syndrome can vary among individuals. Symptoms may slowly change over time from childhood to adulthood.

Infants

Signs and symptoms that may be present from birth include:

• Poor muscle tone. A primary sign during infancy is poor muscle tone (hypotonia). Babies may rest with their elbows and knees loosely extended instead of fixed, and they may feel floppy or like rag dolls when they're held.
• Distinct facial features. Children may be born with almond-shaped eyes, a narrowing of the head at the temples, a turned-down mouth and a thin upper lip.
• Poor sucking reflex. Infants may have a poor sucking reflex due to decreased muscle tone. Poor sucking makes feeding difficult and can result in failure to thrive.
• Generally poor responsiveness. A baby may seem unusually tired, respond poorly to stimulation, have a hard time waking up or have a weak cry.
• Underdeveloped genitals. Males may have a small penis and scrotum. The testicles may be small or not descended from the abdomen into the scrotum (cryptorchidism). In females, the clitoris and labia may be small.

Early childhood to adulthood

Other features of Prader-Willi syndrome appear during early childhood and remain throughout life, requiring careful management. These features may include:

• Food craving and weight gain. A classic sign of Prader-Willi syndrome is a constant craving for food, resulting in rapid weight gain, starting around age 2 years. Constant hunger leads to eating often and consuming large portions. Unusual food-seeking behaviors, such as hoarding food, or eating frozen food or even garbage, may develop.
• Underdeveloped sex organs. A condition called hypogonadism occurs when sex organs (testes in men and ovaries in women) produce little or no sex hormones. This results in underdeveloped sex organs, incomplete or delayed puberty, and in nearly all cases, infertility. Without treatment, women may not start menstruating until their 30s or may never menstruate, and men may not have much facial hair and their voices may never fully deepen.
• Poor growth and physical development. Underproduction of growth hormone can result in short adult height, low muscle mass and high body fat. Other endocrine problems may include underproduction of thyroid hormone (hypothyroidism) or central adrenal insufficiency, which prevents the body from responding appropriately during stress or infections.
• Cognitive impairment. Mild to moderate intellectual disability, such as issues with thinking, reasoning and problem-solving, is a common feature of the disorder. Even those without significant intellectual disability have some learning disabilities.
• Delayed motor development. Toddlers with Prader-Willi syndrome often reach milestones in physical movement — for example, sitting up or walking — later than other children do.
• Speech problems. Speech is often delayed. Poor articulation of words may be an ongoing problem into adulthood.
• Behavioral problems. Children and adults may at times be stubborn, angry, controlling or manipulative. They may throw temper tantrums, especially when denied food, and may not tolerate changes in routine. They may also develop obsessive-compulsive or repetitive behaviors, or both. Other mental health disorders, such as anxiety and skin picking, may develop.
• Sleep disorders. Children and adults with Prader-Willi syndrome may have sleep disorders, including disruptions of the normal sleep cycle and a condition in which breathing pauses during sleep (sleep apnea). These disorders can result in excessive daytime sleepiness and worsen behavior problems.
• Other signs and symptoms. These may include small hands and feet, curvature of the spine (scoliosis), hip problems, reduced saliva flow, nearsightedness and other vision problems, problems regulating body temperature, a high pain tolerance, or a lack of pigment (hypopigmentation) causing hair, eyes and skin to be pale.

When to see a doctor

Regularly scheduled well-baby visits can help identify early signs of poor growth and development, which can be signs of Prader-Willi syndrome or other disorders.

If you have concerns about your baby's health between well-baby visits, schedule an appointment with your child's doctor.

Prader-Willi syndrome is a genetic disorder, a condition caused by an error in one or more genes. Although the exact mechanisms responsible for Prader-Willi syndrome haven't been identified, the problem lies in the genes located in a particular region of chromosome 15.

With the exception of genes related to sex characteristics, all genes come in pairs — one copy inherited from your father (paternal gene) and one copy inherited from your mother (maternal gene). For most types of genes, if one copy is "active," or expressed, then the other copy also is expressed, although it's normal for some types of genes to act alone.

Prader-Willi syndrome occurs because certain paternal genes that should be expressed are not for one of these reasons:

• Paternal genes on chromosome 15 are missing.
• The child inherited two copies of chromosome 15 from the mother and no chromosome 15 from the father.
• There's some error or defect in paternal genes on chromosome 15.

In Prader-Willi syndrome, a defect on chromosome 15 disrupts the normal functions of a portion of the brain called the hypothalamus, which controls the release of hormones. A hypothalamus that isn't functioning properly can interfere with processes that result in problems with hunger, growth, sexual development, body temperature, mood and sleep.

In most cases, Prader-Willi syndrome is caused by a random genetic error and is not inherited. Determining which genetic defect caused Prader-Willi syndrome can be helpful in genetic counseling.

Obesity-related complications

In addition to having constant hunger, people with Prader-Willi syndrome have low muscle mass, so they need fewer than average calories, and they may not be physically active. This combination of factors makes them prone to obesity and the medical problems related to obesity, such as:

• Type 2 diabetes
• High blood pressure, high cholesterol and heart disease
• Sleep apnea
• Other complications, such as an increased risk of liver disease and gallbladder stones

Complications of inadequate hormone production

Complications arising from inadequate hormone production may include:

• Sterility. Although there have been a few reports of women with Prader-Willi syndrome becoming pregnant, most people with this disorder are unable to have children.
• Osteoporosis. Osteoporosis causes bones to become weak and brittle, so they may break easily. People with Prader-Willi syndrome are at an increased risk of developing osteoporosis because they have low levels of sex hormones and may also have low levels of growth hormone — both hormones help maintain strong bones.

Other complications

Other complications that can result from Prader-Willi syndrome include:

• Effects of binge eating. Eating large amounts of food quickly, called binge eating, can cause the stomach to become abnormally enlarged. People with Prader-Willi syndrome may not report pain and they rarely vomit. Binge eating can also cause choking. Rarely, a person may eat so much that it causes stomach rupture.
• Reduced quality of life. Behavioral problems can interfere with family functioning, successful education and social participation. They can also reduce the quality of life for children, teenagers and adults with Prader-Willi syndrome.

If you have a child with Prader-Willi syndrome and would like to have another baby, consider seeking genetic counseling. A genetic counselor may help determine your risk of having another child with Prader-Willi syndrome.

Typically, doctors suspect Prader-Willi syndrome based on signs and symptoms. A definitive diagnosis can almost always be made through a blood test. This genetic testing can identify abnormalities in your child's chromosomes that indicate Prader-Willi syndrome.

Early diagnosis and treatment can improve the quality of life for people with Prader-Willi syndrome. A team of health professionals will likely work with you to manage the condition.

Your team may include a doctor who treats hormonal disorders (endocrinologist), behavior specialists, a dietitian, physical and occupational therapists, a mental health professional, a geneticist, and other specialists as needed.

Although specific treatments vary depending on symptoms, most children with Prader-Willi syndrome will need the following:

• Good nutrition for infants. Many infants with Prader-Willi syndrome have difficulty feeding due to decreased muscle tone. Your child's pediatrician may recommend a high-calorie formula or special feeding methods to help your baby gain weight and will monitor your child's growth.
• Human growth hormone (HGH) treatment. HGH treatment in children with Prader-Willi syndrome helps increase growth, improves muscle tone and decreases body fat. A doctor who treats hormonal disorders (endocrinologist) can help determine whether your child would benefit from HGH and discuss any risks. A sleep study is usually recommended before starting growth hormone treatment.
• Sex hormone treatment. Your endocrinologist may suggest that your child take hormone replacement therapy (testosterone for males or estrogen and progesterone for females) to replenish low levels of sex hormones. Hormone replacement therapy usually starts when your child reaches the normal age for puberty and can help reduce the risk of developing thinning of the bones (osteoporosis). Surgery may be needed to correct undescended testicles.
• Weight management. A dietitian can help you develop a healthy, reduced-calorie diet to help manage your child's weight while ensuring proper nutrition. A restricted-calorie diet may require supplemental vitamins or minerals to ensure balanced nutrition. Increasing physical activity and exercise can help manage weight and improve physical functioning.
• Treatment of sleep disturbances. Treating sleep apnea and other sleep problems can improve daytime sleepiness and behavioral issues.
• Various therapies. Your child will likely benefit from a range of therapies, including physical therapy to improve movement skills and strength, speech therapy to improve verbal skills, and occupational therapy to learn everyday skills. Developmental therapy to learn age-appropriate behaviors, social skills and interpersonal skills also may help. In the U.S., early intervention programs with these types of therapy are usually available for infants and toddlers through a state's health department. During school years, educational planning and support can maximize learning.
• Behavior management. Setting strict limits on behavior, schedules and access to food and strict supervision of food intake may be required. Some people may need medication to manage behavior problems.
• Mental health care. A mental health professional, such as a psychologist or a psychiatrist, may help address psychological problems — for example, obsessive-compulsive behaviors, skin picking or a mood disorder.
• Other treatments. These may include addressing specific symptoms or complications identified by eye exams for vision problems, tests for hypothyroidism or diabetes, and examinations for scoliosis.

Transition to adult care

Most people with Prader-Willi syndrome will need specialized care and supervision throughout their lives. Many adults with the disorder live in residential care facilities that enable them to eat healthy diets, live safely, work and enjoy leisure activities.

As your child approaches adulthood, consider these strategies:

• Find local resources and services for adults through your child's school and organizations such as the Prader-Willi Syndrome Association.
• Investigate guardianship issues, wills and special needs trusts that address future care and supervision for your child.
• Talk to your child's doctor for suggestions about making the transition to adult medical care.

Tips to help you take care of your loved one with Prader-Willi syndrome include the following:

• Learn about Prader-Willi syndrome. Managing hormone levels and weight can improve development and behavior and prevent complications. Work with your health care team to develop a plan of care for managing symptoms and addressing issues.
• Stick to a strict meal plan. Eating a low-calorie diet is essential to keep your child from becoming overweight. Structure mealtime and the type of food to help develop routines and to help your child understand expectations. Use small dishes for serving meals. To help prevent binging, avoid buying high-calorie snacks. Store food out of your child's reach. Lock pantries, refrigerators and cupboards.
• Encourage regular daily activity. Increasing physical activity and exercise can help manage weight and improve physical functioning.
• Set limits. Create a firm schedule and set expectations for managing behavior. If needed, talk to your health care team about ways to address problems.
• Schedule regular medical care. Talk with your doctor about a regular schedule of health appointments and tests to check for problems or complications related to Prader-Willi syndrome.

Having a child with Prader-Willi syndrome is challenging and can take a lot of patience. Managing eating problems, behavior and medical issues can impact the whole family.

Some options for coping and support can include:

• Talking to a mental health professional. If you're having trouble coping or feel overwhelmed, talk to a mental health counselor or therapist.
• Joining a support group. Some people find it helpful to talk with others who share similar experiences. Ask your health care provider about family support groups in your area. Organizations such as the Prader-Willi Syndrome Association provide resources, support groups and educational materials.
• Seeking other sources of support. Options for additional support can include asking about sources of respite care, asking for support from family and friends, and taking time for your own interests and activities.

You may start by seeing your family doctor or your child's pediatrician. He or she may refer you to a pediatric endocrinologist and other specialists as needed.

Here's some information to help you prepare for your appointment. Consider taking a family member or friend along for support and to help you remember information.

What you can do

To prepare for the appointment, make a list of:

• Any signs and symptoms your child has been experiencing, and for how long
• Your child's key medical information, including recent illnesses, medical conditions, and the names and dosages of any medications, vitamins, herbs or other supplements
• Questions you want to ask your doctor

Some basic questions to ask your doctor may include:

• What is likely causing my child's signs and symptoms?
• Are there any other possible causes for these symptoms?
• What kinds of tests does my child need?
• What treatment approach do you recommend?
• What are the expected results of treatment?
• What are the possible side effects of treatment?
• How will you monitor my child's health over time?
• What is my child's risk of long-term complications?
• Can you suggest educational materials and local support services?
• What services are available for early childhood development?

What to expect from your doctor

Your doctor is likely to ask you a number of questions. Be ready to answer them to reserve time to go over points you want to focus on. For example, your doctor may ask different questions depending on your child's age.

Questions about your baby:

• How often and how much does your baby eat?
• Does your baby have any problems sucking?
• How well does your baby wake up?
• Does your baby seem listless, weak or sick?

Questions about early childhood:

• How much does your child eat?
• Does he or she constantly look for food?
• Does your child eat any unusual items or steal or sneak food?
• Does your child show extreme stubbornness or throw tantrums?
• Does your child show any other troubling behaviors?