MLH1 and Lynch syndrome: In addition, the ability of S. cerevisiae Mlh1-Mlh2 to be recruited by mispairs and the mutator phenotype caused by overexpression of MLH2 (and MLH3) suggests that increased expression of human PMS1 (or human MLH3) might represent a mechanism that could lead to MMR inactivation and promote tumorigenesis, analogous to MMR defects in Lynch Syndrome and other types of sporadic cancer characterized by microsatellite instability [1], [3]–[5].