Research finds considerable epigenetic variation in twins
16 August 2010
A longitudinal study of genetically identical (monozygotic) twins has shown that environmental influences play a role in mediating the function of genes. Chloe Wong, a PhD student at the Institute of Psychiatry (IoP) at King’s, found that so-called ‘epigenetic’ differences between monozygotic twins are already detectable in early childhood and can change dynamically over time.
The science of epigenetics – the study of reversible changes in gene function that occur without a change in the DNA sequence – is transforming the nature-nurture debate. It has been speculated that dynamic epigenetic processes, operating at the interface between the genome (nature) and the environment (nurture), make an important contribution to physiological variability and the aetiology of complex diseases. At present, little empirical work has assessed the extent to which epigenetic changes occur over time, and the degree to which such changes are under the influence of heritable and environmental factors. The researchers addressed this by performing a systematic investigation of DNA methylation across three genes (SLC6A4/ SERT, DRD4 and MAOA) widely implicated in common psychiatric disorders using DNA collected at two ages (five and ten years), from a longitudinal study of monozygotic and non-identical (dizygotic) twins.
DNA methylation is a naturally-occurring chemical process which modifies cytosine, one of the four bases of DNA. Once established, such modifications can be inherited through cell division, and play a crucial role in regulating cellular differentiation during normal development in higher organisms. Dr Jonathan Mill, who heads the Psychiatric Epigenetics team said: 'Methylation is often associated with a more compact DNA structure, rendering the genome inaccessible, switching off gene expression or causing genes to be expressed at very low levels. This is important because even if you have two identical strands of DNA, DNA methylation will determine whether the genes are expressed or not.'
Dr Mill added: 'The findings from this study are important because they uncover considerable epigenetic variation, even between genetically-identical individuals, and highlight the potential utility of DNA methylation as a biomarker of environmental influence.' The high level of epigenetic changes over time shown by this study underlines the importance of longitudinal research designs for epigenetic research.
This data could have important implications for the understanding of individual phenotypic differences and susceptibility to disease and the group is currently undertaking genome-wide investigations of DNA methylation for a range of psychiatric disorders.
'A longitudinal study of epigenetic variation in twins' was published in this month’s edition of Epigenetics.