Two of the eight genes differentially methylated in the IUGR group (DECR1 and GSTO1) have been previously associated with IUGR (in animals and singleton humans, respectively), suggesting (at least in part) a common pathogenic mechanism for IUGR in singletons versus that in MC growth-discordant twins [17, 18]. The gene discussed is GSTO1; the disease is fetal growth restriction.