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Infants
Signs and symptoms of Prader-Willi syndrome generally occur in two stages. Signs of the disorder that may be present in the first year of life include:

• Poor muscle tone. A primary sign of Prader-Willi syndrome 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 with Prader-Willi syndrome may be born with almond-shaped eyes, a narrowing of the head at the temples, a turned-down mouth and a thin upper lip.
• Failure to thrive. During the first year of life, children with Prader-Willi syndrome may have a poor sucking reflex due to decreased muscle tone. Because poor sucking makes feeding difficult, they tend to gain weight slowly.
• Lack of eye coordination (strabismus). The eyes of a child with Prader-Willi syndrome may not move together. Therefore, they may cross or wander to the side.
• Generally poor responsiveness. A baby may seem unusually tired, respond poorly to stimulation, wake with difficulty or have a weak cry.

Early childhood
From about ages 1 to 4, other signs of Prader-Willi appear. These problems will remain present throughout life and require careful management or treatment. These signs may include:

• Food craving and weight gain. The classic signs of the disorder are a constant craving for food and a rapid gain in weight. Because a child with Prader-Willi syndrome is always hungry, he or she eats frequently and consumes large portions. A child may develop unusual food-seeking behaviors, such as hoarding food or eating things such as garbage or frozen food.
• Underdeveloped sex organs. A condition called hypogonadism occurs when sex organs — the testes in men and the ovaries in women — produce little or no sex hormones. This results in underdeveloped sex organs, incomplete development at puberty and in nearly all cases infertility. Women may not start menstruating until their 30s, or they may never menstruate. Men may not have much facial hair, and their voices may never fully deepen.
• Poor growth and physical development. Children with Prader-Willi syndrome have low muscle mass. They may have short hands and feet. When a person with the disorder reaches full adult stature, he or she is usually shorter than other family members.
• Learning disabilities. Mild to moderate cognitive impairment is a common feature of the disorder. Essentially all people with Prader-Willi syndrome, even those without significant cognitive disability, have some learning disabilities.
• Delayed motor development. Toddlers with Prader-Willi syndrome often reach milestones in physical movement later than do other children. Sitting up by oneself may be delayed until 12 months and walking until 24 months.
• Speech problems. Speech is often delayed until a child is 2 years of age. Poor articulation of words may be an ongoing problem.
• Behavioral problems. Children may at times be very stubborn or throw temper tantrums, especially when denied food. They may also develop obsessive-compulsive disorder, which results in unwanted, recurring thoughts or repetitive behaviors, or both. Other mental health disorders, such as skin picking or rectal gouging, may develop.
• Sleep disorders. Some children with Prader-Willi syndrome may have sleep disorders, including disruptions of the normal sleep cycle and sleep apnea, a condition in which breathing pauses during sleep. Obesity may worsen sleep disorders.
• Scoliosis. A number of children with Prader-Willi syndrome develop abnormal curvature of the spine (scoliosis).

Other signs and symptoms of Prader-Willi syndrome may include:

• Nearsightedness (myopia)
• Light skin compared with other family members
• High pain tolerance

When to see a doctor
A number of conditions can cause some of the early signs of Prader-Willi, such as a failure to thrive, poor muscle tone and poor sucking. Therefore, it's important to get a prompt and accurate diagnosis.

See your doctor if your infant:

• Has difficulty feeding
• Doesn't wake easily
• Doesn't respond to touch
• Has rag doll-like limbs

See your doctor if your older child shows any of the following signs:

• Rapid weight gain
• Constant hunger
• Unusual food-seeking behaviors

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Prader-Willi syndrome is a genetic disorder, a condition caused by an error in a gene or genes. Although the exact genes responsible for Prader-Willi syndrome haven't been identified, the problem is known to lie in a particular region of chromosome 15.

With the exceptions 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.

However, some types of genes act alone. In other words, it's normal with certain genes for the paternal gene to be expressed and the maternal gene to be "silent."

What happens in Prader-Willi syndrome
Prader-Willi syndrome occurs because certain paternal genes that should be expressed aren't for one of the following reasons:

• Paternal genes on chromosome 15 are missing.
• The person has 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.

The genetic defect of Prader-Willi syndrome disrupts the normal functions of a portion of the brain called the hypothalamus. Among its many functions, the hypothalamus controls hunger and thirst and releases hormones that prompt the release of other substances responsible for growth and sexual development. A malfunctioning hypothalamus — caused by the defect on chromosome 15 — interferes with each of these processes, resulting in uncontrollable hunger, stunted growth, sexual underdevelopment and other characteristics of Prader-Willi syndrome.

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Obesity-related complications
Many of the possible complications of Prader-Willi syndrome result from obesity. In addition to having constant hunger, people with the disorder have low muscle mass, which requires lower than average calorie needs. This combination of factors makes a person prone to obesity and the medical problems related to obesity. These possible complications include:

• Type 2 diabetes. Type 2 diabetes is high blood sugar level due to your body's inability to use insulin efficiently. Insulin plays a vital role in making blood sugar (glucose) — your body's fuel — available to your cells. Obesity significantly increases the risk of diabetes.
• Heart disease and stroke. People who are obese are more likely to have high blood pressure, hardened arteries, high cholesterol, and other factors that can lead to heart disease and stroke.
• Sleep apnea. This sleep disorder is characterized by pauses in breathing during sleep. The disorder can cause daytime fatigue, high blood pressure and, rarely, sudden death. People with Prader-Willi syndrome may have sleep apnea or other sleep disorders even if they aren't obese, but obesity can worsen sleep problems.

Complications of hypogonadism
Other complications arise from hypogonadism, a condition in which your sex organs don't secrete sufficient amounts of the sex hormones testosterone (males) and estrogen and progesterone (females). These 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 (sterile).
• Osteoporosis. Osteoporosis is a condition characterized by weak and brittle bones, which can break easily. People with Prader-Willi syndrome are at an increased risk of developing osteoporosis because they have low levels of sex hormones, which help maintain strong bones.

Other complications
Eating large amounts of food quickly, called binge eating, can cause your child's stomach to become abnormally distended (gastric dilatation). Binge eating can also cause choking and any of the other complications associated with obesity.

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Well-baby visits
If you have a newborn infant, it's important to go to all regularly scheduled well-baby visits. These visits can be important for identifying early signs of poor growth and development — signs of Prader-Willi syndrome and other disorders.

At each visit your child's doctor will measure your baby's height, weight and head circumference. This enables your doctor to track changes and identify problems. The doctor will also test your child's muscle tone by seeing how your child responds to having his or her legs and arms moved. The complete physical exam will include checking the genitals for abnormalities.

Be prepared to answer questions that your baby's doctor is likely to ask:

• 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?

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

Other visits
If you have concerns about your older child's weight gain, eating habits or other behaviors, schedule an appointment with your child's doctor. Your doctor may ask you some of the following questions?

• How much does your child eat?
• Does he or she constantly look for food?
• Is your child extremely stubborn or throw tantrums?
• Does your child show any other troubling behaviors?

If your doctor believes that your child exhibits signs of Prader-Willi syndrome or suggests diagnostic tests for the disorder, consider asking the following questions:

• When will we know the results of the tests?
• How often should we schedule follow-up visits?
• What treatments and care strategies do you recommend?
• How will we know whether the treatment is helping?
• What kind of diet should we follow?
• How many daily calories are appropriate for my child?
• Can you suggest educational materials and local support services regarding Prader-Willi syndrome?
• What services are available for early childhood development?

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In infants, signs that may prompt your doctor to request a blood test for Prader-Willi syndrome include:

• Poor muscle tone
• Almond-shaped eyes
• Narrowing of the head at the temples

In older children, your child's doctor may suspect Prader-Willi syndrome if your child exhibits:

• Behavioral problems
• Weight gain

A definitive diagnosis can almost always be made with a laboratory test. Special genetic tests can identify abnormalities in your child's chromosomes that are characteristic of Prader-Willi syndrome.

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A team of health professionals will likely work with you to manage your child's condition. Most children with Prader-Willi syndrome will need the following care and treatments:

• Good infant nutrition. Many infants with Prader-Willi syndrome have difficulty feeding due to decreased muscle tone. Your child's doctor may recommend a high-calorie formula to help your baby gain weight and will monitor your child's development.
• Growth hormone treatment. Human growth hormone stimulates growth and influences the body's conversion of food into energy (metabolism). Some studies have suggested that growth hormone treatment in children with Prader-Willi syndrome helps increase growth, improve muscle tone and decrease body fat, but the long-term effects of growth hormone treatment aren't known. A doctor who treats hormonal disorders (endocrinologist) can help determine whether your child would benefit from growth hormone treatment.
• Sex hormone treatment. Your endocrinologist may also 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 can help decrease your child's risk of developing thinning of the bones (osteoporosis).
• Healthy diet. As your child gets older, a nutritionist may help you develop a healthy, reduced-calorie diet to keep your child's weight under control while ensuring proper nutrition.
• Overall development. 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 articulation and occupational therapy to learn everyday skills. Developmental therapy to learn age-appropriate behaviors, social skills and interpersonal skills may also be helpful. In the United States, early intervention programs providing these types of therapy are usually available for infants and toddlers through a state's health department.
• Mental health care. A mental health professional, such as a psychologist or a psychiatrist, may help address psychological problems your child may have, such as obsessive-compulsive disorder or a mood disorder. Some children may need medication to control behavioral problems.

Other treatments may be necessary depending on the specific symptoms your child has or complications that develop.

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.

Organizations, such as the Prader-Willi Syndrome Association, can help families find local resources and services.

Also, talk to your child's doctor for suggestions about making the transition to adult medical care.

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

• Pick up your child carefully. Children with Prader-Willi syndrome have poor muscle tone, which increases their risk of slipping between your hands when you lift them under their armpits.
• Take steps to help prevent binge eating. Adhering to a low-calorie diet is essential to keep your child from becoming overweight. Try to avoid purchasing high-calorie snacks. Store food out of your child's reach. Lock pantries, refrigerators and cupboards. Use small dishes for serving meals.
• Supplement your child's diet. If your child is on a restricted-calorie diet, ask your doctor if supplemental vitamins or minerals are necessary to ensure balanced nutrition.
• Schedule appropriate screening tests. Be sure to talk to your doctor about how often you need to have your child screened for complications of Prader-Willi syndrome, including diabetes, osteoporosis and an abnormally curved spine (scoliosis).

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Having a child with Prader-Willi syndrome and its associated behavioral problems is challenging and can take a lot of patience. Some people find it helpful to talk with others who share similar experiences. Ask your doctor about family support groups in your area. Organizations such as the Prader-Willi Syndrome Association provide resources, support groups and educational materials. You can reach the Prader-Willi Association at 800-926-4797.

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Defective or missing portions of paternal genes responsible for Prader-Willi syndrome usually occur randomly. This means that in most instances, Prader-Willi syndrome can't be prevented. However, in a small number of cases, a genetic mutation inherited from the father may cause 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.

©1998-2013 Mayo Foundation for Medical Education and Research (MFMER). Terms of use.
Read this article on Mayoclinic.com.