Prader-Willi syndrome (PWS)

What is Prader-Willi syndrome?

Prader-Willi syndrome is a rare genetic disorder, affecting 1 in every 15,000 individuals.

Prader-Willi syndrome affects many parts of the body causing a wide range of physical symptoms, learning difficulties and behavioural problems. Some symptoms are present from birth, so it’s often recognised and diagnosed within the first few months of life.

In Prader-Willi syndrome a part of the brain known as the hypothalamus doesn’t develop as expected. The hypothalamus has many important functions including releasing hormones, controlling appetite and regulating body temperature. As a result, people with Prader-Willi syndrome are typically obese, as they have no control over how much they eat.

It’s important to get an early diagnosis and treatment to prevent some of the complications associated with Prader-Willi syndrome. The common complications of Prader-Willi syndrome which adversely impact the life of patients include obesity, type 2 diabetes, heart problems and breathing difficulties.

With the right support from a multidisciplinary team to help manage the symptoms, a person with Prader-Willi syndrome can benefit from an improved quality of life. Stimulation programmes to maximise learning potential and promotion of good eating and exercise habits can prolong life expectancy to normal.

Hear advice from other parents whose children are also short in stature, compared with others their age. https://morethanheight.com/en/life-with-growth-disorders/advice-for-early-years-parents-of-a-baby-or-toddler-with-a-growth-disorder/

What causes Prader-Willi syndrome?

Prader-Willi syndrome is a complex genetic disorder caused by a problem on chromosome 15.

Chromosomes store genetic information. Most people have 46 chromosomes organised in 23 pairs. One chromosome in each pair comes from the mother and the other from the father. Both contain the same genes, meaning a person will have two copies of all their genes.

In Prader-Willi syndrome, something has gone wrong causing some of the genes on chromosome 15 to not function correctly. There are several different genetic causes:

In about 65% of cases of Prader-Willi syndrome, some of the genes on chromosome 15 from the father have been mistakenly deleted. This is called “paternal deletion”.

About 30% of cases of Prader-Willi syndrome are caused by a person inheriting two copies of chromosome 15 from their mother, instead of one copy from each parent. This is called “maternal uniparental disomy”.

In less than 5% of cases of Prader-Willi syndrome, both copies of chromosome 15 have been mistakenly “turned off”, so are inactive. This is called “imprinting centre defect”.

Rarely, Prader-Willi syndrome can be caused by a rearrangement of genes on the chromosome, called “translocation”.

The exact genetic cause of Prader-Willi syndrome affects which symptoms are most dominant.

What are the symptoms of Prader-Willi syndrome?

The symptoms of Prader-Willi syndrome vary with age.

In babies:

• Weak muscle tone or floppiness
• Poor sucking reflex and difficulty feeding
• Poor growth with small hands and feet
• Delayed development such as walking and talking
• Underdeveloped genitals (small penis and undescended testicles, small labia and clitoris)

In children:

• Obesity due to extreme food cravings
• Behavioural problems including temper tantrums and skin picking
• Mild to moderate learning difficulties
• Incomplete or delayed puberty
• Poor speech development
• Reduced height

If your child is short in stature, keeping track of their growth can help identify if there is a problem early on. Compare your child’s measurements to the national average to see if they are within a healthy range.

People with Prader-Willi syndrome have certain distinctive features:

• Almond-shaped eyes
• Narrow forehead and bridge of the nose
• Thin upper lip
• Lighter hair, skin and eyes than other family members

A key feature of Prader-Willi syndrome is the constant urge to eat, stemming from an inability to feel full. As a result, people with Prader-Willi syndrome are typically obese, which can cause complications.

What complications are associated with Prader-Willi syndrome?

People with Prader-Willi syndrome are more likely to experience certain health problems, including:

• Eye problems
• Tooth decay
• Osteoporosis (weak bones, making them fragile and more likely to break)
• Scoliosis
• Type 2 diabetes
• Sleep disorders
• Heart failure

How is Prader-Willi syndrome diagnosed?

If your doctor suspects your child to have Prader-Willi syndrome, they will likely refer them for genetic testing. The genetic testing involves taking a sample of your child’s blood, which is tested for any chromosomal abnormalities.

Genetic testing is highly reliable, identifying 99.99% of cases of Prader-Willi syndrome. Your doctor would need to run further tests to identify the genetic type of Prader-Willi syndrome.

Early diagnosis and intervention are important to prevent some of the complications associated with Prader-Willi syndrome. As Prader-Willi syndrome affects many different organs in the body, managing its associated complications often requires a team of different specialists including clinical geneticists, endocrinologists, dieticians and orthopaedic specialists.

It is important you speak to your doctor if you have any concerns about your child’s height. Use this helpful guide on what questions to ask and what to expect from your visit. https://morethanheight.com/en/talk-to-your-doctor/visiting-your-paediatrician/