H19 and omphalocele: A well-defined (epi)genotype–phenotype correlation exists for omphalocele in BWS: it is caused by KCNQ1OT1:TSS-DMR loss of methylation in 86% of the cases, by CDKN1C mutation in 7%, and by UPD or H19/IGF2:IG-DMR gain of methylation in <10% of patients [18].