The molecular basis of BWS is heterogeneous with 5% of patients exhibiting gain of methylation at IC1 with biallelic activation of IGF2 and biallelic silencing of H19. Another group of BWS patients has normal IC1 methylation but abnormal methylation at IC2, a maternally methylated imprinting control region within the KCNQ1 and KCNQ1OT1 gene cluster which seems to operate independent of IGF2 and H19[2]. Here, H19 is linked to Beckwith-Wiedemann syndrome.