The methylated KCNQ1OT1:TSS-DMR form present on the maternal allele prevents the transcription of the long non-coding RNA, KCNQ1OT1, allowing the expression of several genes present in the domain such as CDKN1C. Loss of methylation (LOM) on the maternal allele occurs in 50% of BWS patients (Eggermann et al., 2014; Brioude et al., 2018). This evidence concerns the gene KCNQ1OT1 and Beckwith-Wiedemann syndrome.