PMS2 and Leigh syndrome: LS is caused by mutations in the DNA MMR genes Mlh1, Msh2, Msh3, Msh6, Pms1, and Pms2 (MutL Homolog 1; MutS Homolog 2, 3, and 6; and Post-Meiotic Segregation Increased 1 and 2; respectively) alone or in combination with a germline mutation in the Apc tumor-suppressor gene [116,124].