Diamond-Blackfan anemia (DBA) is a rare congenital red-cell aplasia characterized by anemia, bone-marrow erythroblastopenia, and congenital anomalies and is associated with heterozygous mutations in the ribosomal protein (RP) S19 gene (RPS19) in approximately 25% of probands. We report identification of de novo nonsense and splice-site mutations in another RP, RPS24 (encoded by RPS24 [10q22-q23]) in approximately 2% of RPS19 mutation-negative probands. This finding strongly suggests that DBA is a disorder of ribosome synthesis and that mutations in other RP or associated genes that lead to disrupted ribosomal biogenesis and/or function may also cause DBA.

SummaryA detailed family study was undertaken of patients notified to the UK Diamond Blackfan Anaemia (DBA) Registry. RPS19 mutations were detected in 16 of 104 families, including two patients with deletions detected by intragenic loss of heterozygosity of tightly linked polymorphisms. In two further cases, polymorphisms were used to determine the parental allele of origin of RPS19 point mutations. A review of clinical details of patients with mutations and patients in the literature having identical or equivalent mutations revealed evidence for a genotype:phenotype correlation with respect to the prevalence of physical anomalies, and the occurrence of mild or variable haematological severity. Nine of 60 patients had a known family history of DBA. Haematological abnormalities, including raised red cell adenosine deaminase activity, were found in first-degree relatives of 16 of 51 (31%) of patients not previously considered to have familial DBA. Results of both parents and any siblings were normal in only 35 of 60 (58%) of cases, who were therefore assumed to have sporadic de novo DBA. The classical inheritance pattern for DBA is autosomal dominant; however, 12 of 60 families (20%) had more than one affected child despite normal results in both parents. These results have important implications for genetic counselling, and for the selection of potential sibling bone marrow donors.

The erythroid defect in Diamond Blackfan anemia (DBA) is known to be intrinsic to the stem cell, but its molecular pathophysiology remains obscure. Using a 2-phase liquid erythroid culture system, we have demonstrated a consistent defect in DBA, regardless of clinical severity, including 3 first-degree relatives with normal hemoglobin levels but increased erythrocyte adenosine deaminase activity. DBA cultures were indistinguishable from controls until the end of erythropoietin (Epo)-free phase 1, but failed to demonstrate the normal synchronized wave of erythroid expansion and terminal differentiation on exposure to Epo. Dexamethasone increased Epo sensitivity of erythroid progenitor cells, and enhanced erythroid expansion in phase 2 in both normal and DBA cultures. In DBA cultures treated with dexamethasone, Epo sensitivity was comparable to normal, but erythroid expansion remained subnormal. In clonogenic phase 2 cultures, the number of colonies did not significantly differ between normal cultures and DBA, in the presence or absence of dexamethasone, and at both low and high Epo concentrations. However, colonies were markedly smaller in DBA under all conditions. This suggests that the Epo-triggered onset of terminal maturation is intact in DBA IntroductionDiamond Blackfan anemia (DBA) is a rare congenital red cell aplasia, which classically presents with profound aregenerative anemia in early infancy, often in association with physical anomalies and growth retardation. [1][2][3] The anemia responds to steroid therapy in up to 70% of patients, but eventually around 40% of affected individuals are dependent on long-term transfusion programs. [1][2][3][4] Spontaneous remissions may occur, even in patients who have never previously achieved transfusion independence. [1][2][3][4][5] Sustained remissions have occasionally been reported in response to interleukin-3 (IL-3). 6,7 Recently, clinical responses to prolactin or metoclopramide have been described, but only after prolonged administration. 8 Remissions, whether spontaneous or treatment induced, are usually associated with a residual erythropoietic defect shown by persistent mild anemia and macrocytosis, 1-3 with increased erythrocyte adenosine deaminase (eADA) activity. [9][10][11] The pathophysiologic basis for this characteristic pattern of erythroid failure and remission in DBA remains elusive, even after the identification of the gene encoding ribosomal protein S19 (RPS19) as the first DBA gene, 12 mutated in up to 25% of affected individuals. 13 RPS19 was not an obvious candidate gene for this disorder, being ubiquitously expressed in its normal ribosomal role. Gene transfection studies support the association between RPS19 mutations and impaired erythroid maturation, 14 but the specific contribution of RPS19 to normal and abnormal erythropoiesis has yet to be defined.The demonstration of impaired erythroid differentiation in vitro of enriched erythroid progenitor cells 15 and of purified CD34 ϩ cells 16 from patients with DBA provides strong evidence fo...