Helbig et al. reported that the majority of T-cell clones showed clonal TCRB rearrangements (18/42 patients, 42.8%) in HES patients, whereas clonal rearrangements in the TCRG locus (n = 1) and TCRD locus (n = 2) were rare [38]. The gene discussed is TRGC1; the disease is hypereosinophilic syndrome.