Precision medical epigenetics

Response to treatment and prognosis can be affected by various genetic and non-genetic factors. Since the completion of the first phase of the Human Genome Project in the beginning of the 21st century, the contributions of genetic variations, e.g., in the forms of single nucleotide polymorphisms (SNPs) or copy number variants (CNVs), to individualized drug response as well as final clinical outcomes (e.g., progression-free survival, overall survival) have been appreciated and exploited in precision medicine. However, genetic variation may only explain partially the observed interindividual variability of these phenotypes, while leaving a high proportion of variability unexplained. Epigenetic modifications, as critical genetic regulatory factors, contribute extensively to interindividual natural variation in human populations as well as various biological processes including disease pathogenesis. Technological advances in epigenomic profiling during the past decade have significantly expanded our capability to explore epigenetic modifications, such as cytosine modifications, histone modifications, and microRNAs in clinical specimens and begun to offer opportunities for precision epigenetic medicine. In this chapter, we focused on cytosine modifications, the most extensively investigated epigenetic system to discuss the current advances and challenges of precision epigenetic medicine.