H19 and Silver-Russell syndrome: The expression of IGF2, involved in Beckwith-Wiedemann and Silver-Russell syndromes, is normally inhibited by the insulator H19, which prevents the action of a distal enhancer on the IGF2 promoter; however, in various types of cancer, H19 has been found to be hypermethylated, allowing the expression of the maternal IGF2 copy and causing excess growth factor.