Chromosome pairs affect how our body works. Normally, a baby gets one copy of each chromosome pair from each birth parent. In rare cases, two 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.

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

People with Angelman syndrome (AS) can have traits such as:

• 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.

Prader-Willi syndrome (PWS) can happen when a baby gets both copies of a part of the female parent's chromosome #15. But PWS most often happens when a chromosome #15 from each parent is present, but part of the male parent's chromosome is deleted. Then only the female parent'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 ages 2 and 4, the child becomes obsessed with food. They are not able to control their appetite. They overeat. This often causes fast weight gain, which can lead to the child having obesity and type 2 diabetes.

People with PWS also have:

• Short stature.
• Small hands and feet.
• Intellectual disability.

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