How Is Prader-Willi Syndrome Diagnosed?

Prayer-Willi syndrome, or PWS, is a very rare and complex genetic disorder that causes a number of intellectual, physical, and behavioral issues. Prader-Willi greatly affects metabolism and causes changes in the body and behavior of individuals with the disorder. It is the leading cause of life-threatening childhood obesity due to the constant hunger that children with Prader-Willi often develop as a result of the changes to their metabolism. Children with PWS will usually develop an insatiable hunger around the age of two, one of the main characteristics of the syndrome. In many cases, physical symptoms in a newborn will prompt doctors to begin tests that lead to the diagnosis of Prader-Willi syndrome. The Special Olympics Arizona team is breaking down this diagnosis, the major criteria that are generally present to diagnose PWS and at what age PWS is generally diagnosed.

Diagnostic Criteria for Prader-Willi Syndrome

There are criteria that a child must meet to be formally diagnosed with Prader-Willi syndrome. The criteria that must be met depend on the age of the child: a child under three must meet at least four major criteria and have at least one minor criterion in order to confirm a Prader-Willi syndrome diagnosis. For a child over the age of 3, they must have at least five major criteria and at least three minor criteria for a Prader-Willi syndrome diagnosis. The criteria that a child must meet are as follows:

Major Criteria

Major criteria for individuals to be diagnosed with PWS include:

Extremely weak muscles in the childâ€™s torso.
Difficulty sucking, which may improve after the first few months.
Feeding difficulties that may require feeding assistance, such as feeding tubes or special nipples that aid in sucking.
Failure to grow in the early stages of infancy.
Beginning of rapid weight gain between the ages of 1 and 6 often results in severe obesity.
Excessive, uncontrollable overeating.
Facial abnormalities, such as a narrow forehead or a downturned mouth.
Reduced development of the genital organs, including small genitalia, incomplete or delayed puberty and infertility.
Developmental delays, including intellectual disabilities ranging from mild to moderate and potential learning disabilities.

Minor Criteria

The minor criteria that must be present for individuals to be diagnosed with PWS include:
Decreased movement during infancy.
Noticeable fatigue during infancy.
Behavioral problems, such as temper tantrums, obsessive-compulsive behavior, stubbornness, or stealing and lying, especially when related to food.
Sleep problems, including daytime sleepiness or disruptions throughout the night.
A short stature.
Light color of the skin, eyes, or hair.
Narrow hands and small feet.
Nearsightedness or difficulty focusing both eyes at the same time.
Thick saliva.
Speech difficulties, including poor pronunciation.
Picking of the skin.

Diagnosing Prader-Willi Syndrome

If you notice any of the major or minor symptoms listed above in your baby or child, it is important to speak to a doctor about your concerns. If your child meets the threshold for major and minor criteria, your doctor will conduct testing to confirm the diagnosis of Prader-Willi and help determine a treatment plan and course of action for your child moving forward.

Physical Exam

Your doctor will likely begin with a physical exam to check for the external and recognizable physical symptoms and criteria of Prader-Willi syndrome. In babies, doctors will examine for poor muscle tone, which makes infants feel floppy and is one of the most common symptoms of PWS in babies before the age of three. They will also examine for decreased movement or noticeable fatigue and check if their size and weight are below average for an infant of similar age. They will ask questions about your childâ€™s feeding and how they have grown since birth. For children over the age of three, the doctor will look for symptoms such as obesity, intellectual delays, learning disabilities, and behavioral problems related to food. They may ask questions about your childâ€™s eating habits and how they act in relation to foods in the household. Doctors will verify how many major and minor criteria your child meets for the symptoms of Prader-Willi syndrome.

Genetic Testing

If your child has some of the signs and symptoms of Prader-Willi syndrome, their doctor will likely conduct genetic testing to confirm the diagnosis. Genetic testing can be used to check the chromosomes in a sample of your childâ€™s blood for the genetic changes known to cause Prader-Willi syndrome. High-resolution karyotype is the most common genetic test that will be conducted for a Prader-Willi diagnosis, with a methylation analysis conducted that is known to identify nearly all individuals affected by PWS. Methylation analysis can detect all of the major genetic subtypes of PWS, including deletion, uniparental disomy, and imprinting mutation. In addition to confirming the diagnosis of PWS in your child, genetic testing can also help you determine the likelihood of having another child with PWS.

At What Age Is PWS Diagnosed?

Prader-Willi syndrome is the leading cause of childhood obesity and is characterized by excessive overeating and behavioral difficulties, especially relating to food. Babies with PWS will often have eating difficulties early in life, followed by an insatiable appetite that will develop between the ages of 2 and 6. Due to this insatiable appetite, many children are diagnosed by the time they are 6 years old, but the symptoms in an infant can be recognizable as well. Children can be diagnosed starting in infancy and are most commonly diagnosed before the age of 6.