In PV patients, advancing age correlated with dramatic reductions in total TCRγ and TCRδ (Figure 4A) clonotype counts, driven by loss of the ‘small’ and ‘medium’ TRG and TRD clonotype compartments (Figure 4B, C), and the expansion of the ‘hyperexpanded’ clones (Figure 4B, D). The gene discussed is TRGC1; the disease is acquired polycythemia vera.