Studies of identical (monozygotic) twins: they are epigenetically indistinguishable during the early period of life, but they showed in adult life major differences in the distribution of 5-methylcytocism DNA and histone acetylation. Approximately one-third of the twins had epigenetic differences in DNA methylation and histone acetylation. This work demonstrated that different phenotypes can be found in individuals with the same genotype. In one identical twin study, it was found that there could be a 20-30% variance in behaviour in adult life. (Mustard, J. Fraser, MD. Early Childhood Development: How does experience in early life affect brain development? 2008. p. 15.)