BRAF and Leigh syndrome: In addition, patients with LS colorectal cancer rarely carry BRAF gene, while those without LS colorectal cancer have a mutation rate of 68%.[20] The specificity of MSI in patients with MMR mutations is 90%,[18] The sensitivity of detection is 80% to 91% in patients with MLH1 or MSH2 gene mutation and 55% to 77% in patients with MSH6 or PMS2 gene mutation.