Abnormal methylation of tumour suppressor genes

• Abnormal DNA methylation can lead to the development of tumours. Specifically, hypermethylation (increased methylation) can cause cancer.
• Hypermethylation occurs in the promoter region of tumour suppressor genes, leading to the inactivation of tumour suppressor genes. Consequently, transcription of the promoter regions of tumour suppressor genes is inhibited, meaning the genes are switched off. This inactivation leads to increased cell division and the formation of a tumour.
• Since the tumour suppressor gene normally slows the rate of cell division, its inactivation leads to increased cell division and hence tumour formation.
• Hypermethylation is thought to occur in the tumour suppressor gene known as BRCA1, leading to the development of breast cancer.
• Hypomethylation is another form of abnormal methylation, whereby methylation is reduced. This typically occurs in oncogenes, leading to their activation and hence the formation of tumours.