Imprinting may be defined as parental origin-dependent, epigenetic marking of the genome. At some loci, these imprints have demonstrated effects on gene expression, such that the allele inherited from only one parent is transcribed. The epigenetic nature of genome imprints raises the possibility that environmental factors can alter the establishment or stability of these allele-specific marks in somatic or germilne cells. Because many imprinted genes encode products that are involved in embryogenesis or cell proliferation, it is possible that disruptions to the establishment or maintenance of genome imprints may result in developmental abnormalities or lead to cancer. Curiously, approximately one-eighth of the human population appears to have altered imprinted gene expression at the insulin-like growth factor two locus. We will determine whether this disruption of imprinting is most likely to be due to genetic, environmental or stochastic factors and also determine whether genome imprints have remained stable over a period of nearly two decades.