Anticipation is seen in-

Fragile X syndrome is the prototype of diseases in which the causative mutation occurs in a long repeating sequence of three nucleotides Anticipation: This term refers to the phenomenon whereby clinical features of fragile X syndrome worsen with each successive generation, as if the mutation becomes increasingly deleterious as it is transmitted from a man to his grandsons and great-grandsons. (Robbins Basic Pathology,9th edition,pg no. 241)