Prader-Willi syndrome

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.

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.

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.