Accumulating passenger mutations in blood stem cells provide a direct measure of clonal expansion during human aging. Scientists long assumed only specific cancer driver mutations caused these blood stem cell clones to outgrow their neighbors. Instead, dividing stem cells copy passive genetic tags that multiply whenever shared cellular growth pathways activate.
As hematopoietic stem cells divide over decades, harmless background mutations embed quietly across the genome. These neutral genetic markers hitchhike through cell divisions like copier smudges duplicated on every new page. Inherited genetic variations alter DNA methylation, chromatin structure, and RNA splicing, accelerating the growth of specific stem cell clones. The resulting clonal growth concentrates altered regulatory elements within active blood progenitor cells.
Researchers analyzed 791,067 whole-genome sequences from the UK Biobank and the All of Us Research Program. Their multi-ancestry association study identified 81 genetic locations linked to passenger mutation burden, including 42 novel regions. Rare-variant testing confirmed that genes including MBD2, PRKACB, and PUF60 regulate clonal fitness while passenger burden correlates strongly with blood cancer and mortality.
Tracking passenger mutations now allows researchers to map the shared genetic architecture governing aging blood across diverse global ancestries. Spatial modeling of passenger burdens across American regions also enables scientists to detect unexplained geographic variations in blood aging beyond differences in income, air quality, or chemotherapy.