Abstract
Epigenetic alterations are heritable changes in gene expression without an accompanying change in primary DNA sequence. Two major mechanisms that cause epigenetic changes are post-translational histone modifications and DNA methylation at cytosine bases within a CpG dinucleotide. Epigenetic defects have turned out to be one of the most common molecular alterations in human neoplasia. Promoter hypermethylation is associated with loss of expression of tumour suppressor genes in cancer. The analysis of aberrant DNA methylation is gaining strength in the fields of cancer risk assessment, diagnosis, and therapy monitoring in different cancer types. These issues are discussed in this review.
Highlights
Cytosine methylation occurs after DNA synthesis by enzymatic transfer of a methyl group from the methyl donor S-adenosylmethionine to the carbon-5 position of cytosine
They report two patients, who fit the criteria for hereditary nonpolyposis colorectal carcinoma (HNPCC), with soma-wide, allele-specific and mosaic hypermethylation of MLH1 and no evidence of genetic mutations in mismatch repair genes
A study where the CpG island methylator phenotype (CIMP) status, characterized by concurrent methylation of multiple CpG islands in tumour DNA, was evaluated in 103 stage III colorectal cancer samples from patients treated with surgery alone and in an additional 103 cases from patients treated with surgery and adjuvant 5-fluorouracil-based chemotherapy
Summary
Cytosine methylation occurs after DNA synthesis by enzymatic transfer of a methyl group from the methyl donor S-adenosylmethionine to the carbon-5 position of cytosine. The generally accepted definition of a CpG island was proposed in 1987 by Gardiner-Garden and Frommer They defined it as a 200-bp stretch of DNA with a G+C content of 50% and an observed. Takai and Jones used the complete genomic sequences of human chromosomes 21 and 22 to examine the properties of CpG islands in different sequence classes [88]. They found that regions of DNA of greater than 500 bp with a G+C equal to or greater than 55% and observed CpG/expected CpG of 0.65 were more likely to be associated with the 5’ regions of genes and this definition excluded most Alu-repetitive elements.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
