The p57Kip2 is located at an imprinted locus and loss-of-function mutations in p57Kip2 cause Beckwith-Wiedemann syndrome, an overgrowth disorder which is characterized by increased organ sizes including that of muscles [44,45], and gain-of-function mutations cause undergrowth disorders such as Silver-Russell syndrome [46–48]. This evidence concerns the gene CDKN1C and Silver-Russell syndrome.