Overview of Prader-Willi Syndrome
Prader-Willi syndrome is a rare genetic disorder that results in several physicals, mental and behavioural problems. A key feature 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.
Causes of Prader-Willi syndrome
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.
Except for 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 counselling.
Symptoms of Prader-Willi syndrome
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.
The complications of PWS can include having unusual reactions to medications, especially sedatives and anaesthesia.
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.
Typically, doctors can suspect 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. 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), behaviour 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 this syndrome have difficulty feeding due to decreased muscle tone. Your child’s paediatrician 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. The 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.