Uniparental Disomy: Prader-Willi Syndrome and Angelman Syndrome

What is uniparental disomy?

Chromosome pairs affect how our body works. Normally, a baby gets 1 copy of each chromosome pair from each parent. This means 1 copy from the genetic mother, and the other copy from the genetic father. In rare cases, 2 copies come from the same parent. This is called uniparental disomy. Angelman syndrome (AS) and Prader-Willi syndrome (PWS) are disorders that can be caused by uniparental disomy.

What is Angelman syndrome?

Angelman syndrome can happen when a baby gets both copies of a part of chromosome #15 from the father. But AS most often happens when a chromosome #15 from each parent is present, but part of the mother’s chromosome is deleted. Then only the father's part is present. This causes AS symptoms to occur. 

People with Angelman syndrome (AS) can have these traits:

• Smaller head

• A wide jaw and spaced-out teeth

• Puffy-looking eyelids

• Short stature

• Severe intellectual disability with a lack of speech

• Stiff arm movements

• Spastic, uncoordinated walk

• Seizures

• Random outbursts of laughter

What is Prader-Willi syndrome?

Prader-Willi syndrome (PWS) can happen when a baby gets both copies of a part of chromosome #15 from the mother. But AS most often happens when a chromosome #15 from each parent is present, but part of the father’s chromosome is deleted. Then only the mother’s part is present. This causes PWS symptoms to occur. 

Babies born with PWS:

• Have poor muscle tone

• Have a weak cry

• Start as slow feeders

• Appear undernourished

The feeding problems improve after infancy. Between 2 to 4 years of age, the child becomes obsessed with food. They are not able to control their appetite. They overeat. This often causes fast weight gain, obesity, and type 2 diabetes.

People with PWS also have:

• Short stature

• Small hands and feet

• Intellectual disability

Talk with a genetic counselor

Talk to your healthcare provider or a genetic counselor to learn more about uniparental disomy.