Genomic Imprinting Syndromes and Cancer

Genomic imprinting is an epigenetic phenomenon that leads to parent-specific differential expression of a subset of mammalian genes. Some imprinted genes are expressed from the maternal allele and repressed on the paternal allele, whereas others are expressed from the paternal and not the maternal allele. Because most imprinted genes play important roles in growth and development, and metabolism, the aberrant expression of imprinted genes due to epigenetic or genetic alterations often causes human disorders. These include genomic imprinting syndromes and tumors. Since loss of imprinting (LOI) of IGF2 (which means biallelic expression of IGF2) was first reported in Wilms tumor in 1993, aberrant methylation of differentially methylated regions (DMRs), which regulate expression of imprinted genes and/or aberrant expression of imprinted genes, have been reported in various tumors. In this section, general imprinting mechanisms, representative clinical features and causative molecular alterations of eight imprinting syndromes are described. In addition, representative molecular alterations of imprinted DMRs or imprinted genes associated with tumors are also described.