Low-heteroplasmy mitochondrial DNA mutations improve clonal reconstruction of human cells

Reconstructing clonal relationships among human cells is fundamental to understanding development, aging, and disease. Somatic mitochondrial DNA (mtDNA) mutations act as endogenous single-cell barcodes measurable alongside cell-state profiles, but lineage tracing has traditionally focused on high-heteroplasmy variants, which are easier to detect but few and potentially shaped by selection. Whether the more abundant lower-heteroplasmy variants encode bona fide lineage information has not been tested against an independent clonal reference. Using lentiviral barcoding of human hematopoietic cells to establish ground-truth clone identities, we show that after stringent molecule-level error filtering, mutation calls below 10% per-cell heteroplasmy account for roughly half of all lineage-informative calls. Retaining the full heteroplasmy spectrum approximately doubled the clonal-assignment area under the precision-recall curve relative to a >10% cutoff, and single-molecule-supported calls improved recovery when retained collectively. These findings establish lower-heteroplasmy mtDNA mutations as an abundant, bona fide record of clonal history, substantially expanding the clonal resolution attainable in human tissues without genetic engineering.