What is Prader-Willi syndrome?

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PWS is a genetic condition, which means that people inherit it from their parents.

It is present from birth, although a diagnosis often does not occur until later in life.

People with PWS have seven genes on chromosome 15 that are either deleted or inactive.

They will often have low muscle tone, incomplete sexual development, and chronic hunger.

Their metabolism tends to burn fewer calories when compared to people who do not have the condition. Many individuals with PWS have short stature.

A new-born infant with PWS tends to have a lower-than-usual birth weight, weak muscles, and difficulties with sucking. Muscle weakness is known as hypotonia.

Individuals start developing a strong appetite called hyperphagia between 2 and 5 years of age and sometimes later.

This characteristic occurs due to a significantly decreased feeling of fullness after eating. Once hyperphagia begins, it tends to be a lifelong condition.

Symptoms of PWS typically develop in two stages.

The first symptoms often emerge during the first year of life, and others start to occur between the ages of 1 and 6 years old.

Symptoms in the first year

Between 0 and 12 months of age, an infant is likely to have some or all of the following symptoms:

• Hypotonia, or poor muscle tone: The child feels floppy when another person is holding them. The elbows and knees may be loosely extended instead of firmly in position. Hypotonia improves with age.
• Specific facial features: These may include almond-shaped eyes and a head that narrows at the temples. The mouth might have a small, turned-down appearance with a thin upper lip.
• Reduced physical development: Poor muscle tone can reduce sucking ability, making feeding difficult. The infant may gain weight at a slower rate than other babies.
• Strabismus: The eyes do not move in unison. One eye may appear to wander, or the eyes may cross.

The infant may also have an unusually weak cry, display incomplete responses to stimulation, and appear tired.

Genitals may not develop correctly, and depigmentation of the skin and eyes sometimes occurs.

Symptoms from age 1 to 6 years

Between 1 and 6 years of age, the following symptoms may occur:

• Food cravings and gain in body weight: The child craves food constantly, eating large amounts of food with great frequency. They may hoard food or eat items that most people would not, such as frozen food before it is thawed or cooked or food that has passed its expiry date.
• Hypogonadism: The testes or ovaries do not produce enough sex hormones, resulting in underdeveloped sex organs. The testes of males with PWS may not descend.
• Limited growth and strength: This can include poor muscle mass, as well as small hands and feet. People with PWS may not reach full height, as an adult, due to a shortage of growth hormone.
• Limited cognitive development: This might lead to mild to moderate learning disabilities.
• Delayed motor skills: Children might reach the common milestones of progress in learning coordination skills, such as sitting up or walking, later than usual. The infant may not walk until 24 months old.
• Delayed verbal skills: A child with PWS may develop their speech capabilities later than is typical.
• Behavior and mental disorders: These may include temper tantrums, especially relating to food. The child may be argumentative, oppositional, rigid, manipulative, possessive, and stubborn. Some children may have obsessive-compulsive disorder (OCD), repetitive behaviors, recurring thoughts, and other mental disorders. Excessive skin-picking and nail-biting may occur.
• Sleep disorders: These may include sleep apnea, possibly due to obesity. There may be disturbances of the normal sleep cycle.
• Scoliosis or curvature of the spine: This is a symptom that can occur as the individual with PWS grows.
• Depigmentation: The skin and hair may be fairer than that of parents and siblings.

There may be a high tolerance for pain. Short-sightedness is also common.

The Prader-Willi Syndrome Association is now increasingly seeing PWS as a syndrome of multiple stages rather than just the two used initially.

In Phase 2, at 18 to 36 months, body weight crosses over from being lower than average to higher without any additional interest in food or calorific intake.

Phase 3 starts around the age of 8 years and can carry on to adulthood. Relentless food-seeking begins and is a key feature of this stage.

Going forward, people with PWS undergo poor sexual development during puberty. Females may experience scant menstruation or none at all, and most adults with PWS may not be able to reproduce.

Parents should consult a doctor if the following signs appear:

• difficulty feeding at the infant stage
• problems waking up
• a lack of response to normal stimulation
• floppiness when held
• the constant seeking of food in a child
• rapid weight gain

Other warning signs include constant hunger, continual searching for food, and, usually, rapid weight gain. There will almost always be other signs, though, and most children who exhibit these behaviors do not have PWS.

Genetic anomalies cause PWS. Researchers have found the abnormality on chromosome 15, but they have not yet identified the genes involved.

Besides those related to sex, all human genes come in pairs. One copy is from the father and called the paternal gene, and the other copy is from the mother and known as the maternal gene.

In PWS, certain paternal genes on chromosome 15 are either missing or not functioning correctly.

This genetic anomaly changes how the hypothalamus works. The hypothalamus is a part of the brain that controls thirst and hunger. It also releases hormones that promote sexual development and growth.

If the hypothalamus is damaged, for example, through a head injury, tumor, or tumor-removal surgery, PWS-like signs and symptoms may develop.

Despite not having the genetic features of PWS, the person with a damaged hypothalamus may acquire some of the same behavioral problems, such as constant food cravings.

The treatment used for people born with PWS can also help those with acquired symptoms similar those common to the condition.

A number of tests are available for PWS, but a type of genetic testing called DNA methylation can detect 99 percent of cases.

Early testing is necessary, as early diagnosis makes timely treatment possible.

Some people with PWS do not receive a diagnosis, or they are given a misdiagnosis of Down’s syndrome or autism spectrum disorder (ASD), as some features of these conditions overlap with those of PWS.

There is no cure for PWD.

However, ongoing therapies can help reduce symptoms by focusing on related hormone and developmental deficiencies.

Therapies that doctors might use include:

• nutrition
• growth
• sex hormones
• physical
• speech
• occupational
• developmental

Nutrition therapy can supply an infant who is experiencing feeding difficulties with high-calorie milk formula.

A doctor who is treating PWS will closely monitor weight and growth, while a nutritionist may assist in developing a nutrient-dense, low-calorie diet that promotes weight control.

People with PWS must follow a very strict diet with lower-calorie goals than would be common for the age group. Parents and guardians may have to put physical barriers in place to account for food cravings, such as locking food inside kitchen cabinets.

Growth hormone treatment can help increase growth and reduce body fat, but the long-term effects of these are unclear.

Sex hormone treatment, such as hormone replacement therapy (HRT), can top up testosterone for boys and progesterone for girls. This helps with sexual development and can reduce the risk of osteoporosis.

Other treatments include:

• developmental therapy to encourage age-appropriate social and interpersonal skills
• occupational therapy to help with routine tasks
• physical therapy to manage coordination and movement
• speech therapy to promote communication ability

A person with PWS may also need to consult a psychologist or psychiatrist for help with the psychological effects of PWS.

Most people with PWS need supervision and specialized care throughout their lives. Continually restricting food and managing behavior can cause stress for family members, and family support and counseling groups can sometimes offer help.

The complications of PWS can include having unusual reactions to medications, especially sedatives and anesthesia.

A person with PWS may have a typically high pain threshold, meaning that an infection or illness does not receive medical attention until its later stages. Vomiting is also rare in people with PWS unless a problem is already severe.

The high prevalence of obesity means a higher risk of type 2 diabetes, heart disease, and stroke than in other people. Similarly, people with PWS have a higher rate of tooth erosion than others. Osteoarthritis and osteoporosis, affecting the bones and joints, might also occur.

PWS is a condition in which an individual cannot control the urge to eat due to a chromosomal anomaly, as well as delayed growth and poor cognitive development, among other symptoms.

The symptoms develop in stages, and early identification can help an individual manage the condition.

If a person with PWS can control both obesity and the other complications of the condition, they can expect few, if any, changes to life expectancy.

However, individual medical supervision is essential throughout life, and particularly once a person with PWS reaches 40 years of age.