Despite a low percentage of myPCs in the blood of HD (median: 0.03% of CD45+ leukocytes), we were able to analyze the myPC compartment in a remarkably large number of samples independent of disease status: in 92% of newly diagnosed MDS, 87% of nonCR-MDS, 87% of nonMDS-cytopenias, 82% of CR-MDS, and all HDs, respectively. The gene discussed is PTPRC; the disease is myelodysplastic syndrome.