Repairing the Epigenetics of Unstable Repeats by Genome Engineering

Epimutations are the cause of a considerable number of genetically inherited conditions in humans. All result from the mis-expression of genes due to epigenetic changes that are triggered by an underlying heritable mutation. The correction of these epigenetic defects in the context of epigenetically regulated diseases constitutes a good paradigm to probe the fundamental mechanisms underlying the development of these diseases, and the molecular basis for the establishment, maintenance and regulation of epigenetic modifications in general. Here, we review current applications of key editing tools to address the epigenetic aspects of these diseases by focusing on epimutations caused by, or relate to repetitive elements, primarily unstable noncoding repeat expansions. For each approach we summarize the efforts conducted to date, highlight their contribution to a better understanding of the molecular basis of epigenetic mechanisms, describe the limitations of each approach and suggest perspectives for further exploration in this field.