MSH6 and Leigh syndrome: However, LS is vastly underdiagnosed, with estimates that it is as common as one in 279 of the general population (MLH1 = one in 1946, MSH2 = one in 2841, MSH6 = one in 758, and PMS2 = one in 714) [7], and accounts for approximately 3% of CRCs and ECs [8,9].