Diagnosis

A definitive diagnosis of Prader-Willi syndrome can usually be made by running a series of genetic tests.

Genetic testing

Genetic testing can be used to check the chromosomes in a sample of your child's blood for the genetic abnormalities known to cause Prader-Willi syndrome.

As well as confirming the diagnosis, the results should also allow you to determine the likelihood of having another child with the syndrome.

Read more about the causes of Prader-Willi syndrome.

Checklist for diagnosing Prader-Willi syndrome

A checklist of symptoms known to be typical of Prader-Willi syndrome is also used to identify which children should be tested.

The checklist can also be helpful for parents concerned about their child's development, behaviour and eating habits, and who want to know whether their child may have Prader-Willi syndrome.

Major criteria

One point is given for each of the following symptoms a child has:

• floppiness and weak muscles, becoming apparent during or shortly after birth
• feeding problems and failure to grow during the first year of life
• rapid weight gain in children aged 1 to 6 years
• characteristic facial features, such as almond-shaped eyes and thin upper lips
• underactive testicles or ovaries (hypogonadism), resulting in delayed sexual development
• delayed physical development or learning difficulties

Minor criteria 

Half a point is given for each of the following symptoms a child has:

• lack of movement during pregnancy, such as kicking in the womb, or an unusual lack of energy after birth
• sleep disturbances, such as sleep apnoea
• delayed or absent puberty
• unusually fair hair, skin and eyes
• narrow hands
• thick and sticky saliva
• crossed eyes or long-sightedness (hyperopia)
• problems pronouncing words and sounds properly
• frequent skin picking

Overall score

If your child is under the age of 3 and scores 5 points, with at least 3 points from the major criteria, Prader-Willi syndrome would be strongly suspected and genetic testing would be recommended.

If your child is over the age of 3 and scores 8 points, with at least 4 points from the major criteria, Prader-Willi syndrome would be strongly suspected and testing would be recommended.

Page last reviewed: Fri Jan 2021 Next review due: Wed Feb 2020