Prader-Willi syndrome

Prader-Willi syndrome is a rare genetic disorder that affects development and growth. It is thought that around one in 10,000 to 20,000 children are born with the syndrome, with females slightly more likely to be affected than males. There is no cure, but care from a range of specialists can greatly improve a child’s quality of life.

Signs in early childhood#

A baby with Prader-Willi syndrome is typically unusually floppy at birth, with feeding difficulties and a weak cry. Boys often have testes that have not moved down into the scrotum (undescended testes) and may have underdeveloped genitalia. Around half of all affected children have fair skin, blonde hair and blue eyes, regardless of how their family members look.

Children with the syndrome are delayed across all areas of development, reaching milestones such as sitting, crawling and walking later than other children. The average IQ is around 70, but the degree of intellectual disability varies from child to child.

By about five years of age, a characteristic feature emerges: an excessive appetite that can lead to obesity if it is not carefully managed.

What causes Prader-Willi syndrome#

Humans have 23 pairs of chromosomes, with one set inherited from each parent. Prader-Willi syndrome is caused by missing or non-working genes on the copy of chromosome 15 that comes from the father. This can happen in several ways:

• The father’s copy of chromosome 15 is altered, usually because genes are deleted. This is the most common cause, accounting for about 60 to 70 per cent of cases.
• The child inherits two copies of chromosome 15 from the mother and none from the father. This happens in about 25 to 30 per cent of cases.
• A translocation occurs, where some genes on the father’s copy of chromosome 15 are shuffled around or swapped with genes from other chromosomes.
• The father’s copy of chromosome 15 is intact, but the genes in the Prader-Willi region do not work properly.

The genetic change occurs by chance#

In almost all cases the genetic change happens by chance and is not inherited from a parent.

Appetite and weight#

At birth, affected children suck poorly and may not grow at the expected rate. This changes remarkably between one and four years of age, when an excessive appetite develops and children become prone to obesity.

This is a major challenge for children and their families, but it can be managed with careful attention to diet and behaviour. As children get older they can also develop a range of associated health and behavioural problems, which may include temper tantrums and obsessive or compulsive behaviours such as skin picking.

Associated problems#

Problems linked with Prader-Willi syndrome can include:

• Obsessive and compulsive behaviours, such as picking at the skin
• Eye problems, such as short-sightedness
• Short stature, often due to growth hormone deficiency
• Delayed onset of puberty, and delayed or absent menstrual periods in girls
• An abnormally small penis in boys
• Scoliosis (sideways curves in the spine) and kyphosis (an exaggerated hump in the spine)
• Type 2 diabetes
• Osteoporosis (weakened bones that are prone to fracturing)
• Teeth problems, including soft enamel and tooth grinding
• Sleep apnoea (breathing stops for a time during sleep)
• Problems with short-term memory

Diagnosis and treatment#

Prader-Willi syndrome is diagnosed by physical examination and blood tests that check for problems with chromosome 15. There is no cure and it cannot be prevented, so treatment aims to ease the associated problems.

Depending on the needs of the person, treatment options may include:

• Strict supervision of diet, as there is no medication that curbs the appetite
• Plenty of physical activity to help keep body weight in a healthy range
• Growth hormone treatment to address the deficiency that contributes to short stature and to increase muscle mass
• Hormone therapy to boost inadequate sex hormone levels
• Medication to help control obsessive and compulsive behaviours
• Orthopaedic treatment for scoliosis or kyphosis
• Appropriate prescription glasses

Specialist care is important#

Children with Prader-Willi syndrome benefit enormously from coordinated specialist care. Health professionals involved often include a primary care doctor, a paediatrician (a doctor who specialises in treating children), a dietitian, a physiotherapist, a speech therapist, a dentist, an optician and a behavioural psychologist.

Genetic counselling#

If your child has been diagnosed with Prader-Willi syndrome, it may help to speak to a genetic counsellor. Genetic counsellors are health professionals qualified in both counselling and genetics. As well as providing emotional support, they can help you understand the syndrome, what causes it and what the diagnosis means for your child’s health and development. They are trained to provide information and support that is sensitive to your family circumstances, culture and beliefs.

Support groups can also connect you with other individuals and families affected by Prader-Willi syndrome.

Key points#

• The most common cause is a deletion on the father’s copy of chromosome 15, accounting for about 60 to 70 per cent of cases.
• The genetic change that causes Prader-Willi syndrome occurs by chance and is not inherited.
• There is no cure for Prader-Willi syndrome and it cannot be prevented.
• Treatment aims to ease the associated problems and improve quality of life.

Where to get help#