Definition

Prader-Willi (PRAH-dur VIL-e) syndrome is a rare disorder present at birth 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 usually have trouble controlling their weight. Many complications of Prader-Willi syndrome are due to obesity. If you or your child has Prader-Willi syndrome, a team of specialists can work with you to manage symptoms, reduce the risk of developing complications and improve quality of life.

Symptoms

Infants with Prader-Willi syndrome

Signs and symptoms of Prader-Willi syndrome generally occur in multiple phases. Signs 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.
Failure to thrive. Infants 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 child’s eyes may not move together — they may cross or wander to the side.
Generally poor responsiveness. A baby may seem unusually tired, respond poorly to stimulation, have a hard time waking up or have a weak cry.

Early childhood to adulthood

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

Food craving and weight gain. Classic signs and symptoms include constant craving for food and rapid weight gain. Because a child with Prader-Willi syndrome may always be 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 — testes in men and 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. Without treatment, women may not start menstruating until their 30s, or they may never menstruate, and 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 and high body fat. They may have small hands and feet. When a person with the disorder reaches full adult stature, he or she is usually shorter than other family members.
Intellectual disability. Mild to moderate impairment in intellectual functioning, such as thinking, reasoning and problem-solving (intellectual disability), 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. They may not tolerate changes in their routine. They may also develop obsessive-compulsive or repetitive behaviors, or both. Other mental health disorders, such as skin picking, may develop.
Sleep disorders. Adults and 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. These disorders can result in excessive daytime sleepiness and worsen behavior problems. Obesity may worsen sleep disorders.
Scoliosis. A number of children with Prader-Willi syndrome develop abnormal curvature of the spine (scoliosis).
Other endocrine problems. These may include insufficient production of thyroid hormone (hypothyroidism), growth hormone deficiency or central adrenal insufficiency, which prevents the body from responding appropriately during stress or infections.

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

Nearsightedness (myopia) and other vision problems
Light skin and hair compared with other family members
High pain tolerance, making it difficult to identify injury or illness
Problems regulating body temperatures during fever or in hot and cold places

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. So it’s important to get a prompt and accurate diagnosis. See your health care provider if your child shows any signs or symptoms listed above.

Causes

Prader-Willi syndrome is a genetic disorder, a condition caused by an error in one or more genes. Although the exact genes responsible for Prader-Willi syndrome haven’t been identified, the problem lies 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.

However, some types of genes act alone. For example, with certain genes it’s normal for the paternal gene to be expressed and the maternal gene to be “silent,” or repressed.

What Happens in Prader-Willi Syndrome

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.

Prader-Willi syndrome disrupts the normal functions of a portion of the brain called the hypothalamus. The hypothalamus controls hunger and thirst and releases hormones that prompt the release of other substances responsible for growth and sexual development. A hypothalamus that isn’t functioning properly — 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.

Complications

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, so they require fewer than average calories. This combination of factors makes a person prone to obesity and the medical problems related to obesity, such as:

Type 2 diabetes. Type 2 diabetes affects the way your body metabolizes blood sugar (glucose), due to your body’s inability to use insulin efficiently. Insulin plays a vital role in making blood sugar (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.
Other complications. Obese people, including those with Prader-Willi syndrome, are at increased risk of liver disease and can have pain in their joints due to excessive wear and tear.

Complications of Hypogonadism

Complications may also 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.
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 and may also have low levels of growth hormone — both hormones help maintain strong bones.

Other Complications

Other complications can arise from the complex nature of Prader-Willi syndrome:

Effects of binge eating. Eating large amounts of food quickly, called binge eating, can cause your child’s stomach to become abnormally distended (gastric dilatation). Individuals with Prader-Willi syndrome may not report pain and they rarely vomit. Binge eating can also cause choking and any of the other complications associated with obesity. Rarely, a person with Prader-Willi syndrome may eat so much that it causes stomach rupture.
Significant behavior problems. Behavioral problems can interfere with family functioning and successful education and social participation. They can also reduce the quality of life for children, teenagers and adults with Prader-Willi syndrome.

Source: Mayo Clinic