Normally, we inherit one copy of each chromosome pair from our biological mother, and the other copy of the chromosome pair from our biological father. Uniparental disomy refers to the situation in which two copies of a chromosome come from the same parent, instead of one copy coming from the mother and one copy coming from the father. Angelman syndrome and Prader-Willi syndrome are examples of disorders caused by uniparental disomy.
People with Angelman syndrome (AS) have mental retardation, severe speech problems, stiff arm movements, and a stiff, uncoordinated walk. They may have seizures and often have inappropriate outbursts of laughter. Angelman syndrome results when a baby inherits both copies of a section of chromosome #15 from the father (rather than one from the mother and one from the father).
Prader-Willi syndrome (PWS), on the other hand, results when a baby inherits both copies of a section of chromosome #15 from the mother. Babies born with PWS have poor muscle tone and a weak cry. They initially are slow feeders and appear undernourished. The feeding problems improve after infancy and often between 2 to 4 years of age the child becomes obsessed with food and is unable to control their appetite. The overeating often results in rapid weight gain and obesity. Individuals with PWS are mentally retarded and less-than-average adult height.
Consult your physician or genetic counselor for more information regarding uniparental disomies.