Specific EEP and LEP defects in DBA. (A) EEP and LEP were quantified by flow cytometry. Representative plots from a patient with TD DBA, SR DBA, and an age-matched control are shown. Values refer to frequency of CD71⁺CD41a⁻ cells as a % of MEP, and frequency of EEP and LEP as a % of CD34⁺Lin⁻ population. (B) Frequency of BM EEP in TD DBA (n = 10), SR DBA (n = 5), and control BM (n = 9) as assessed by flow cytometry. (C) Frequency of BFU-E colonies generated from 100 flow-sorted DBA and control EEP (n = 4). (D) Clonogenicity of TD DBA (n = 4), SR DBA (n = 3), and control EEP (n = 6) flow-sorted as single cells. (E) Frequency of LEP in TD DBA (n = 10), SR DBA (n = 5), and control BM (n = 9) as assessed by flow cytometry. (F) Clonogenicity of DBA TD (n = 2; due to insufficient LEPs in TD DBA BM for sorting) and control (n = 4) LEP after sorting and plating of 100 cells. (G) Clonogenicity of TD DBA (n = 2), SR DBA (n = 3), and control LEP (n = 5) flow-sorted as single cells. (H) Proliferative capacity of flow-sorted DBA and control EEP in a longitudinal liquid culture (Protocol B; supplemental Materials and methods) assessed by cell counting (n = 4). Cells on day 11 were a pure population of erythroblasts (ie, CD34⁻CD71⁺GlyA⁺CD14⁻CD11b⁻CD41a⁻). (I) Left: BM erythroblasts arising downstream of EPs were identified as Lin⁻ (not shown) CD34⁻CD71⁺ BM mononuclear cells (top panel) co-expressing CD36 and GlyA (bottom panel). Representative flow cytometry plots from a control, a TD patient with DBA, and a DBA patient successfully treated with steroids are shown. Right: Cumulative data from controls (n = 8), TD (n = 10), and steroid-treated (n = 5) DBA patients. Data are shown as mean ± SEM. *P < .05; **P < .01; ***P < .001; ****P < .0001.