KCNQ1 and Beckwith-Wiedemann syndrome: Although a CDKN1C promoter mutation might explain reduced CDKN1C expression in BWS cases with either loss of methylation within KvDMR or a KCNQ1 deletion, this was not considered to be a likely possibility given the rarity of CDKN1C mutation and the extremely unlikely scenario that two distinct constitutional mutations may have caused the syndrome in this instance.