There were no significant methylation differences between other tumor sub-groups (MSS/MSI-L) and normal tissue samples (S8 Fig); however, there was a clear trend of higher levels of MLH1 promoter methylation among rhesus sporadic MSI-H compared to MSS tumors as well as a notorious absence of MLH1 methylation in the only LS tumor tested, which is consistent with human CRC biology. This evidence concerns the gene MLH1 and Leigh syndrome.