The use of assisted reproductive technologies (ART) has become increasingly common worldwide and is now responsible for 2-3% of children born in developed countries. Multiple reports have suggested that ART-conceived children are more likely to develop rare epigenetic disorders such as Beckwith-Wiedemann Syndrome or Angelman Syndrome, both of which involve dysregulation of imprinted genes. Anecdotal reports suggest that animals produced with ART that manifest apparent epigenetic defects typically do not transmit these epimutations to subsequent generations when allowed to breed naturally, but this hypothesis has not been directly studied. We analyzed allele-specific DNA methylation and expression at three imprinted genes, H19, Snrpn, and Peg3, in somatic cells from adult mice generated with the use of intracytoplasmic sperm injection (ICSI), a type of ART. Epimutations were detected in most of the ICSI-derived mice, but not in somatic cells of their offspring produced by natural mating. We examined germ cells from the ICSI mice that exhibited epimutations in their somatic cells and confirmed normal epigenetic reprogramming of the three imprinted genes analyzed. Collectively, these results confirm that ART procedures can lead to the formation of primary epimutations, but while such epimutations are likely to be maintained indefinitely in somatic cells of the ART-derived individuals, they are normally corrected in the germ line by epigenetic reprogramming and thus, not propagated to subsequent generations.gametogenesis | transgenerational inheritance E arly embryos and germ cells are unique in that they must undergo extensive epigenetic reprogramming to reestablish developmental potency during each generation. This reprogramming entails erasure of most inherited epigenetic modifications followed by the acquisition and subsequent maintenance of new epigenetic profiles (1). Genomic imprinting is an epigenetic phenomenon found in eutherian and metatherian mammals (2) that results in parent-of-origin-specific, monoallelic expression of a subset of genes (3). This functional asymmetry of imprinted genes is conferred through differential DNA methylation patterns established during gametogenesis in each parent that distinguish the maternal and paternal alleles in the ensuing offspring (4, 5). These regions are known as differentially methylated regions (DMRs), and the differential methylation profiles at these genetic elements play an important role in regulating allele-specific expression of imprinted genes (3).Because the epigenome is distinct in each cell type and is readily reversible by developmental reprogramming, it is particularly susceptible to disruption by environmental influences (6). Such epigenetic defects are known as "epimutations" and can be of two types-primary epimutations or secondary epimutations (7). Primary epimutations result from a direct disruption of an epigenetic parameter such as DNA methylation that is then propagated through DNA replication to subsequent cells. Secondary epimutations result...