MSH6 and neoplasm: MSH6-deficient cells are unable to repair single base mismatches, whereas they retain proficiency to repair two, three and four base loops (Drummond et al, 1995; Risinger et al, 1996; Umar et al, 1997), thus, causing only mononucleotide repeat instability in tumours (Wagner et al, 2001; Plaschke et al, 2004).