Epigenetic status in the offspring of spontaneous and assisted conception

Abstract

Study question: Is DNA methylation in buccal cell DNA from children born following IVF (in vitro fertilization) and ICSI (intra-cytoplasmic sperm injection) different from that of spontaneously conceived children?

Summary answer: DNA methylation in the imprinted gene, small nuclear ribonucleoprotein polypeptide N (SNRPN), was higher in children conceived by ICSI and in those born to women with the longest duration of infertility regardless of the method of conception.

What is known already: Fertility treatment is associated with a small but significant increase in the risk of a range of adverse obstetric outcomes, birth defects and longer term sequelae, but the biological basis for this is unknown. A growing evidence base suggests that epigenetics may play a role in subfertility and the link between fertility and health.

Study design, size, duration: In this retrospective cohort study of children born between 2002 and 2008, we measured DNA methylation in paternally expressed gene 3 (PEG3), insulin-like growth factor II (IGF2), SNRPN, long interspersed nuclear element 1 (LINE1) and the insulin gene (INS) in buccal cell DNA from children born following IVF (n = 49) and ICSI (n = 20) and compared them with a matched spontaneous conception group (n = 86).

Participants/materials, setting, methods: Participants were identified from the Aberdeen Maternity and Neonatal Databank and IVF and ICSI pregnancies were matched to spontaneous conception pregnancies on year of birth and maternal age at delivery. Only singleton pregnancies following fresh embryo transfer were included. DNA methylation was determined by pyrosequencing. Regression with adjustment for covariates was used to determine the effect of infertility on offspring DNA methylation.

Main results and the role of chance: SNRPN methylation in the offspring was linked to fertility treatment in the parents. This effect was specific to children conceived using ICSI and was apparent in the comparison of ICSI versus spontaneous conception (1.03%; 95% CI 0.10, 1.97; P = 0.031), ICSI versus standard IVF (1.13%; 95% CI 0.04, 2.23; P = 0.043) and ICSI versus standard IVF and spontaneous conception (1.05; 95% CI 0.15, 1.94; P = 0.023). In all comparisons, the use of ICSI was associated with a higher level of SNRPN methylation in the offspring. A higher level of SNRPN methylation in the offspring was also associated with a longer duration of infertility in the parents. This was observed in all cases of infertility (0.18% per year of infertility; 95% CI 0.02, 0.33; P = 0.026) and after excluding ICSI cases (0.21% per year of infertility; 95% CI 0.04, 0.37; P = 0.017). There was a significant increase in the level of LINE1 methylation with age between birth and 7 years (0.77% per year; 95% CI 0.49, 1.05; P < 0.001). Methylation in the INS gene decreased significantly over the same period (-0.46% per year; 95% CI -0.89, -0.03; P = 0.035). There was no evidence from this cross-sectional data that methylation within the imprinted genes changed over the first 7 years of life.

Limitations, reasons for caution: The ICSI sample size was limited but the groups were carefully selected and well matched and the SNRPN findings were consistent across different outcomes.

Wider implications of the findings: The results of this study provide support for a role for epigenetics, and imprinting in particular, in fertility. The specific changes point to possible long-term consequences of fertility treatment for the health and fertility of future generations.

Study funding/competing interest(s): The authors report no conflict of interest in relation to this work. Funding was provided by the University of Aberdeen and the Scottish Government.

Trial registration number: Not applicable.