Characterizing mutations associated with constitutional mismatch repair deficiency syndrome (CMMRD) in Saccharomyces cerevisiae

Abstract

DNA mismatch repair (MMR) is a highly conserved mechanism that is critical for the preservation of genome integrity. Constitutional mismatch repair deficiency syndrome (CMMRD) is a recessively-inherited childhood cancer predisposition disease caused by biallelic mutations in one of four MMR genes, MLH1, MSH2, MSH6, or PMS2. Individuals with CMMRD are at increased risk of developing a broad spectrum of malignancies, including hematological, brain, and intestinal tract tumors. Explanations for clinical trends in age of onset of malignancy and severity of clinical outcome in CMMRD patients are currently not well-tested. In this study, we characterized human mutations associated with CMMRD in terms of MMR function in the budding yeast, Saccharomyces cerevisiae. CMMRD-associated mutations in MSH6 and MLH1 were introduced in the cognate positions in the yeast genes. We performed qualitative and quantitative analyses of MMR function conferred by the mutations. Mutations in MLH1 led to a much greater defect in MMR function than did mutations in MSH6. Functional assay results suggest a correlation between CMMRD outcome and the least deleterious allele. Characterization of CMMRD-associated mutations has important implications for elucidating observed clinical trends and developing guidelines for diagnosis, surveillance, treatment, and genetic counseling for this disorder.