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. This evidence concerns the gene CDKN1C and Beckwith-Wiedemann syndrome.