[DNA methylation. From basic research to routine diagnostics].

On a molecular level cancer is characterized not only by genetic defects, such as deletions, mutations or translocations, but also by epigenetic lesions. The most important epigenetic mechanisms are DNA methylation, Polycomb/trithorax complexes, histon modifications, non-coding RNAs, and chromosomal territories. These epigenetic mechanisms contribute to a stable modification of gene expression without changes in primary DNA sequence. During the development and progression of human tumours a gene-specific hypermethylation with resulting repression of transcription can occur. At the same time, global hypomethylation can very often be observed which contributes to an increase in chromosomal instability. In tumour pathology, the detection of somatic hMLH1 hypermethylation is important for molecular diagnostics of Lynch syndrome. The detection of MGMT gene methylation is a good prognostic and predictive factor for glioblastoma patients. Performing DNA methylation assays for routine diagnostics requires technical as well as theoretical expertise.