This review focuses on the mechanisms of DNA methylation, DNA methylation pattern formation and their involvement in gene regulation. Association of DNA methylation with imprinting, embryonic development and human diseases is discussed. Furthermore, besides considering changes in DNA methylation as mechanisms of disease, the role of epigenetics in general and DNA methylation in particular in transgenerational carcinogenesis, in memory formation and behavior establishment are brought about as mechanisms based on the cellular memory of gene expression patterns.
Turner syndrome (TS) is an interesting model for investigating the association between methylenetetrahydrofolate reductase (MTHFR) gene polymorphisms and non-disjunction because of the high frequency of chromosomal mosaicism among patients with this syndrome. We determined the frequencies of MTHFR 677C ® T and 1298A ® C polymorphic mutations in 49 patients with TS and 200 control individuals. The frequency of the 677C ® T allele was 0.39 for patients and 0.29 for controls while that of the 1298A ® C allele was 0.28 for patients and 0.25 for controls. Genotype frequencies were shown to be different in patients and controls (c 2 = 12.143; p = 0.033), and this was attributable to the higher frequency of the C677C ® T /677C ® T genotype among TS patients. In homozygotes, this mutation might have an effect on somatic chromosome disjunction by decreasing MTHFR activity.
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