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Somatic Mutation in Normal Bladder Study

Adult human somatic tissues are landscapes of mutant clones, but little is known about how these landscapes are shaped by known cancer risk factors. The goal of this study was to determine how the main bladder cancer risk factors (sex and smoking) change the mutational landscape of the normal urothelium. We collected normal urothelium from 45 donors at autopsy by brushing ~2cm² of the surface epithelium in the upper part (dome) and lower part (trigone) of the bladder (79 samples total). To identify mutations with high sensitivity we employed ultradeep (~5000x) DNA error-correcting duplex-sequencing on a panel of 15 protein coding genes and the TERT promoter, previously described to be under positive selection in normal urothelium or relevant to bladder cancer.

We identified thousands of clonal driver mutations, which demonstrate pervasive positive selection in the normal urothelium. Males showed a significantly higher number of driver truncating mutations in RBM10, CDKN1A and ARID1A, despite similar rates of non-coding mutations, indicating stronger positive selection and clonal expansion in the male urothelium. We also discovered clonal expansions driven by activating TERT promoter mutations in the normal bladder, which were strongly associated with age and smoking. These results demonstrate that sex and smoking shape the clonal landscape of the normal bladder and indicate that the high mutational content of normal tissues might be leveraged to study the effect of mutations in vivo (i.e. natural saturation mutagenesis).

We will deposit in dbGaP de-identified relevant clinical information from the 45 donors and the fastq files derived from duplex sequencing of the 79 samples in the study. We will also deposit fastq files derived from duplex sequencing of 3 control cord blood samples.