When comparing tumours with a missense (but not a truncating) mutation in APC to tumours with a truncating mutation in APC, missense mutations occurred relatively more frequently in the colon (P = 0.002), less often also harboured an activating K-ras mutation (P = 0.004), and more often also lacked hMLH1 expression (P < 0.001). The gene discussed is MLH1; the disease is neoplasm.