Most BWS patients have genetic or epigenetic errors at the H19/IGF2 and/or the CDKN1C/KCNQ1OT1 clusters, such as DNA methylation perturbations, copy-number variants and loss-of-function mutations of imprinted genes (Table 1). This evidence concerns the gene KCNQ1OT1 and Beckwith-Wiedemann syndrome.