Detection and significance of NPM1 mutations in blood DNA of healthy individuals. (A) Approach used to identify NPM1 gene mutations in WES of blood DNA from 200 453 UKBB participants. (B) Alignment of sequencing reads from the 2 cases with NPM1 mutations against reference type A (left) and type D (right) NPM1 mutations. This identified 4 reads reporting the type A mutations in case 1 (left) and 1 read reporting the type D mutation in case 2 (right). Mutant reads (black horizontal bars) match perfectly with their respective reference mutant sequences, whereas wild-type reads (colorless horizontal bars) align with a 4-nucleotide gap at the insertion/duplication hotspot. (C) Timeline, gene mutations, and outcomes of the 2 individuals with NPM1 mutations. Both cases were also found to harbor mutations in the DNMT3A gene, whilst case 1 also harbored an internal tandem duplication in the FLT3 gene. (D) Forest plot of hazard ratios for hematological malignancies, myeloid malignancies, AML, and MDS associated with a high MCV (MCV > 99.5 fl) in the UKBB. CI, confidence interval; HR, hazard ratio; MCV, mean corpuscular volume; MDS, myelodysplastic syndrome.