Up to 15% of the MLH1-deficiencies in sporadic colon cancers appeared to be due to over-expression of the microRNA miR-155, which represses MLH1 expression.[45] However, the majority of 68 sporadic colon cancers with reduced expression of the DNA mismatch repair protein MLH1 were found to be deficient due to epigenetic methylation of the CpG island of the MLH1 gene.[46]