Clinical and laboratory evidence for a trilineage haematopoietic defect inpatients with refractory Diamond-Blackfan anaemia

Diamond-Blackfan anaemia (DBA) is a constitutional pure red cell aplasia pr esenting in early childhood. In some patients, neutropenia and/or thrombocy topenia have also been observed during the course of the disease. We have f ollowed 28 patients with steroid-refractory DBA for up to 13 years with ser ial peripheral blood counts and bone marrow (BM) aspirates and biopsies. In 21/28 (75%) patients, moderate to severe generalized BM hypoplasia develop ed, with overall cellularities ranging from 0% to 30%, Marrow hypoplasia co rrelated with the development of neutropenia (9/21: 43%) and/or thrombocyto penia (6/21; 29%) in many patients. No patient had either cytogenetic abnor malities or progressed to acute leukaemia, although one 13-year-old develop ed marked marrow fibrosis and trilineage dysplasia, We used the in vitro lo ng-term culture-initiating cell (LTC-IC) assay to quantify multilineage, pr imitive haematopoietic progenitors in a representative subset of these pati ents. LTC-IC assays showed equivalent frequencies of cobblestone area formi ng cells (CAFCs) with a mean of 5.42/10(5) cells +/- 1.9 SD and 6.13/10(5) cells +/- 2.6 SD in nine patients and six normal controls respectively, The average clonogenic cell output per LTC-IC, however, was significantly lowe r in DBA patients (mean 2.16 +/- 1.2 SD vs. 7.36 +/- 2.7 SD in normal contr ols, P = 0.0008). Our results suggest that the underlying defect in patient s with severe refractory DBA may not be limited to the erythroid lineage, a s was evidenced by the development of pancytopenia, bone marrow hypoplasia and reduced clonogenic cell output in LTC-IC assays.