The genetic code is comprised of the four bases adenine (A), guanine (G), thymine (T), and cytosine (C). Determining their sequence is done using whole genome sequencing. Whole genome sequencing can give insight into variations in the genetic code, including single nucleotide variants (SNVs), small insertions and deletions (indels), copy number variants (CNVs), and structural variants. These variations can play a pivotal role in diseases. Thus, whole genome sequencing can contribute, amongst others, to disease research, cancer studies, personalized medicine approaches, and translational medicine.
However, whole genome sequencing does not capture the epigenome of a cell. In Epigenomics, the changes in gene function are studied that are not due to changes in the genome sequence, e.g., due to mutations or recombination. These epigenetic changes in gene function are passed on to daughter cells. This is done, for example, by methylation of cytosines. Especially cytosines that are followed by guanines, so-called CpG regions, are modified. If the fifth carbon position is modified with a methyl group, a 5-methylcytosine (5mC) is generated. The oxidation of this 5mC results in the formation of 5-hydroxymethylcytosine (5hmC). This DNA methylation can be associated with altered gene expression. Methylated cytosines are, for example, present at transcription start sites of repressed genes. However, methylation can also be associated with gene activation, e.g., during development. Thus, revealing the methylation pattern of a cell can have pivotal implications for the understanding of biological processes, such as aging, but also for diagnosing diseases, such as cancer, atherosclerosis, cardiovascular diseases, or nervous disorders.