Epigenetics is the study of heritable phenotype changes that affect gene activity and expression that do not involve alterations in the DNA sequence. Currently, DNA methylation is one of the most broadly studied and well-characterized epigenetic modifications. Other major modifications include chromatin remodeling, histone modifications, and non-coding RNA mechanisms. Epigenetic modifications play important roles on development, differentiation and disease progression such as various cancers, mental retardation associated disorders, immune disorders, neuropsychiatric disorders and pediatric disorders.