Uniparental Disomy

Does this test have other names?

Genetic testing for Angelman syndrome, genetic testing for Prader-Willi syndrome

What is this test?

This is a blood test used to see if your child has certain chromosome changes.

Normally, people have 23 pairs of chromosomes in their cells. In each pair, one chromosome comes from their father and one from their mother. These chromosomes contain genes.

Sometimes people will inherit two copies of a chromosome or a part of a chromosome from their mother or father, but none from their other parent. This is called uniparental disomy. In some cases this causes health problems.

Two medical conditions that are often linked to uniparental disomy are Prader-Willi syndrome and Angelman syndrome. In some of these cases, the person is missing chromosome 15 from one parent. This blood test can help find out if a child has uniparental disomy related to one of these syndromes. 

Why does my child need this test?

Children may have genetic testing to help diagnose them with Prader-Willi or Angelman syndrome. Making the diagnosis of Prader-Willi or Angelman syndrome early in life can help doctors and parents plan for early intervention.

Symptoms of Prader-Willi syndrome often include:

• Difficulty feeding as a baby but an unusually strong appetite beginning as a toddler

• Obesity

• Undescended testicles and small penis in boys

• Learning problems

• Delayed puberty and abnormal sexual development

Symptoms of Angelman syndrome often include:

• Small head size

• Developmental problems

• Unusually frequent laughing and smiling

• Notably happy and excitable demeanor

• Frequent flapping hand gestures

• Trouble communicating

• Trouble walking 

What other tests might my child have along with this test?

A child's symptoms help doctors determine a diagnosis of Prader-Willi or Angelman syndrome. Your child may need a variety of genetic tests to confirm the diagnosis and figure out if symptoms are caused by uniparental disomy. 

What do my child's test results mean?

Many things may affect your child's lab test results. These include the method each lab uses to do the test. Even if your child's test results are different from the normal value, your child may not have a problem. To learn what the results mean for your child, talk with your child's health care provider.

The results of gene testing can tell you if your child has one of these disorders and, if so, whether uniparental disomy is the cause. The cause of the syndrome may influence how the problem affects your child. For instance, when uniparental disomy is the cause of Angelman syndrome, children are less likely to have a small head, seizures, and certain other complications. 

How is this test done?

The test requires a blood sample, which is drawn through a needle from a vein in your child's arm. A blood sample from your child and both parents may be needed.

Does this test pose any risks?

Taking a blood sample with a needle carries risks that include bleeding, infection, bruising, or feeling dizzy. When the needle pricks your child's arm, he or she may feel a slight stinging sensation or pain. Afterward, the site may be slightly sore. 

What might affect my child's test results?

No medications or conditions will affect your child's test results.  

How do I get my child ready for this test?

Your child doesn't need to prepare for this test.