Mutation significance and estimated clonality of mutations determined the most likely MSI target genes to be the aminoadipate-semialdehyde dehydrogenase <i>AASDH</i> and the solute transporter <i>SLC9A8</i> Our findings offer a systematic profiling of the somatic background mutation rate in protein-coding mononucleotide microsatellites, allowing a full cataloging of the true targets of MSI in colorectal cancer.<i></i>.