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

Genetic testing

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

This will not only confirm the diagnosis of PWS, but should also be able to determine exactly what type of chromosome defect is responsible for your child's condition.

This information should allow you to determine the likelihood of having another child with PWS.

Read more about the causes of Prader-Willi syndrome.

Checklist for diagnosing Prader-Willi syndrome

A checklist of symptoms known to be typical of PWS is also thought to be very useful for identifying which children should be tested.

This checklist is also helpful for parents concerned about their child's development, behaviour and eating habits, and who want to know whether their child may have PWS.

Major criteria

Score one point for each symptom your child has:

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

Minor criteria 

Score half a point for each symptom that your child has:

• lack of movement during pregnancy, such as kicking in the womb, or the baby appears unusually lacking in 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
• problems pronouncing words and sounds properly
• frequent skin picking

Total score

If your child is under the age of three and scores five points, with at least three points from the major criteria, a diagnosis of PWS would be strongly suspected and genetic testing would be recommended.

If your child is over the age of three and scores eight points, with at least four points from the major criteria, a diagnosis of PWS would be strongly suspected and testing recommended.