Definition:

Beckwith-Wiedemann syndrome (BWS) is an imprinting disorder characterized by overgrowth, tumor predisposition, and congenital malformations. It is associated with genetic or epigenetic abnormalities in a cluster of imprinted genes found within a genomic region of approximately one megabase on chromosome 11p15. The imprinted region 11p15 is separated into two domains, with each domain regulated by a functionally independent imprinting control regions (ICR). The centromeric ICR2 regulates the expression of CDKN1C, KCNQ1, and further genes. The majority of cases of BWS show hypomethylation in the ICR2 or mutations in the ICR2-regulated CDKN1C gene. In intron 10 of the KCNQ1 locus, the untranslated KCNQ1OT1 RNA is encoded. KCNQ10T1 is expressed by the paternal allele and probably represses realization of the CDKN1C gene. In the telomeric ICR1, hypermethylation of the H19 promoter and loss of imprinting of IGF2 have been reported in a small fraction of patients with BWS. A few BWS cases could be related to NSD1 deletions or mutations.