In view of the results from animal studies, it has become important to establish whether diseases linked to imprinting defects are more prevalent in children conceived through ARTs. Indeed, in 2003, a series of case reports suggested that BWS is more prevalent amongst such children [7, 10, 51]. BWS is a rare disorder with an estimated incidence of 1 in 13 700 infants. As the disease is characterized by overgrowth, it shares many of the features of LOS. BWS is a polygenic disorder and several imprinted loci contribute to disease development, including the Igf2 and H19 loci. However, these initial case reports were criticized for being poorly controlled and for their reliance on questionnaire data to determine the method of conception. These case reports were followed by a case–control study in 2004 by Halliday et al. . Of 37 children with BWS, four were conceived through IVF. In the control group consisting of 148 healthy children, only one child was born after IVF. This study showed that children conceived by IVF are significantly more likely (odds ratio 17.8; 95% confidence interval 1.8–436.9) to have BWS, compared with naturally conceived children. The authors concluded that children with BWS born after IVF procedures had a loss of methylation at the imprinted KvDMR/LIT1 locus. However, in a study of 185 phenotypically normal children, there were no significant differences between those conceived through IVF, through ICSI or naturally at any of the nine differentially methylated regions (DMRs) investigated (including KvDMR1, H19, SNRPN, GRB10, DLK1/MEG3 IG-DMR, GNAS NESP55, GNAS NESPas, GNAS XL-alpha-s and GNAS Exon1A), in the maternal peripheral blood, the umbilical cord blood or the amnion/chorion tissue . Other studies have not identified an increased prevalence of BWS or other imprinting-associated disorders as a consequence of ARTs [27, 29, 33, 54, 55].
Until recently, studies were either small in size, or attempts were made to link the children born with BWS to dysregulated imprinting of genes known to be associated with BWS. Imprinting disorders such as BWS are polygenic, and it is not yet known which additional genomic loci might be influenced through the process of assisted reproduction. Thus, it is possible that the epigenetic effects of these procedures are greatly underestimated. Recent advances in profiling the epigenetics of DNA samples allow for genome-wide approaches to investigate the effects of ARTs on imprinting. This data-driven approach has the potential to identify yet unknown genes that are affected in children conceived through ARTs (i.e. genes that are not necessarily associated with specific clinical manifestations). Recently, Katari et al.  investigated patterns of epigenetic modifications using this data-driven approach. The methylation patterns of more than 700 genes were analysed in 10 children conceived in vitro and 13 conceived naturally. The results showed that there were differences in methylation levels of several genes, including some that have been implicated in chronic metabolic disorders, such as obesity and type II diabetes. Furthermore, genome-wide DNA methylation together with chromatin organization was also investigated in human embryos produced by either IVF or ICSI. Similar findings were observed in both groups, leading to the conclusion that ICSI does not result in an increased incidence of epigenetic errors (DNA methylation and chromatin) compared with IVF .
Results from studies in sperm suggest that male infertility may contribute to epigenetic effects in pregnancies through ARTs. Altered methylation patterns in imprinted loci have been reported from infertile men (both those with abnormal protamine expression and oligozoospermic patients), compared with fertile donors [58–62]. However, there were differences in the statistical significance of the results between the infertile groups, suggesting that the risk of transmission of epigenetic alterations may differ according to the underlying cause of male infertility. Furthermore, the methylation imprinting marks of two oppositely imprinted genes, H19 and MEST/PEG1, were studied in human testicular spermatozoa from patients with azoospermia of different aetiologies. It was found that spermatozoa from men with abnormal spermatogenesis carry methylation defects in the H19 imprinted gene, which also affect the CCCTC-binding factor-binding site, further supporting an association between the occurrence of imprinting errors and disruptive spermatogenesis . However, it should be noted that these studies do not provide a causal link for epigenetic inheritance of imprinting diseases. More detailed information about the human sperm epigenome can be found elsewhere [58, 60, 64].