UV signature mutation hyperhotspots as genomic dosimeters.

Screening for UV-sensitive DNA mutation sites as dosimeters for individual sun exposure, using high-fidelity Duplex Sequencing to reduce false positives and a stringent genome alignment protocol to reduce false negatives, revealed: (i) Sun-exposed human skin contained UV signature mutations (C → T at a diypyrimidine) >1000-fold more frequently than unexposed neonatal skin, making these mutations sensitive genomic dosimeters for UV exposure. (ii) Tumor suppressor gene hotspot nucleotides (nt) reached variant allele frequency (VAF) 0.1%-10% via 30-3000 fold clonal expansion in occasional biopsies, due to being cancer drivers. (iii) Cyclobutane pyrimidine dimer (CPD) hyperhotspots attained those frequencies in nearly every biopsy, due to profuse creation plus ~30-fold clonal expansion. (iv) Neonatal keratinocyte cultures exposed to weeks of low-dose UVB exposure developed mutations at skin cancer tumor suppressor gene hotspot nt rarely and randomly, as expected. (v) CPD hyperhotspots in gene promoters acquired mutations in days at 1000-fold higher frequencies. Sun exposure is the strongest risk factor for skin cancer, so quantifiable UV signature mutations at CPD hyperhotspots in normal skin may make it technically feasible to identify individuals in need of monitoring to ensure early detection.