What are some examples of genomic imprinting disorders?

Common examples of these conditions include Angelman syndrome and Prader-Willi syndrome. Both conditions result from the absence of specific genetic material on chromosome 15. 

Angelman syndrome arises when the UBE3A gene is dysfunctional or entirely absent. The maternal copy of this gene is normally active, while the paternal copy is silenced or inactive.

In Prader-Willi syndrome, within certain genes of chromosome 15, the copy inherited from the mother is silenced while the copy inherited from the father remains active. The majority of these 2 conditions occur because of deletions. 

Another imprinting condition is Russel-Silver syndrome. Researchers believe that 30-50% of these conditions arise from alterations in methylation of the short (p) arm of chromosome 11 at position 15 (11p15).