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Investigations of Genetic Variation in Families Affected by MUTYH-Associated Polyposis

Defects in the Base-Excision Repair gene, MUTYH, are known to increase colorectal cancer risk through a recessive Mendelian pattern and raise mutation rates in both normal somatic and germline mammalian cells. In this study, we employed whole genome sequencing (WGS) of fifteen human individuals (representing 4 related families) at 50X coverage to examine germline de novo mutation rates in a large family with pathogenic MUTYH mutations and a history of colorectal cancer. We used an in vitro cell line assay to determine the family's genotype (p. Y179C/V234M, transcript NM_001128425) partially attenuates MUTYH's function. The children of mothers affected by the biallelic pathogenic genotype were associated with a moderate increase in the C>A mutation rate, but this effect was determined to be lower than previously reported mutator effects for other biallelic pathogenic MUTYH genotypes. No similar mutation rate increase was found in children of fathers with the same genotype despite calculating that we should have adequate power to detect such a mutator effect, indicating that MUTYH's role in repairing oxidative stress might be more significant in female reproductive aging than in males.

We used a combination of in vitro cell line assays and bioinformatics pipelines to assess the impact of the MUTYH genotype on germline mutation rates. The study design ensures that sufficient statistical power was available to detect mutator effects in both maternal and paternal lineages. The sequencing data generated from this study include single sample genotype files derived from WGS, focusing on germline DNA. The phenotypic data at individual level and sequence data can be accessed by authorized users, facilitating further exploration of the relationship between MUTYH pathogenic variants and colorectal cancer risk.