Diamond-Blackfan Anemia (DBA) is characterized by a defect of erythroid progenitors and, clinically, by anemia and malformations. DBA exhibits an autosomal dominant pattern of inheritance with incomplete penetrance. Currently nine genes, all encoding ribosomal proteins (RP), have been found mutated in approximately 50% of patients. Experimental evidence supports the hypothesis that DBA is primarily the result of defective ribosome synthesis. By means of a large collaboration among six centers, we report here a mutation update that includes nine genes and 220 distinct mutations, 56 of which are new. The DBA Mutation Database now includes data from 355 patients. Of those where inheritance has been examined, 125 patients carry a de novo mutation and 72 an inherited mutation. Mutagenesis may be ascribed to slippage in 65.5% of indels, whereas CpG dinucleotides are involved in 23% of transitions. Using bioinformatic tools we show that gene conversion mechanism is not common in RP genes mutagenesis, notwithstanding the abundance of RP pseudogenes. Genotype–phenotype analysis reveals that malformations are more frequently associated with mutations in RPL5 and RPL11 than in the other genes. All currently reported DBA mutations together with their functional and clinical data are included in the DBA Mutation Database.

Stem-bulge RNAs (sbRNAs) are a group of small, functionally yet uncharacterized noncoding RNAs first described in C. elegans, with a few homologous sequences postulated in C. briggsae. In this study, we report on a comprehensive survey of this ncRNA family in the phylum Nematoda. Employing homology search strategies based on both sequence and secondary structure models and a computational promoter screen we identified a total of 240 new sbRNA homologs. For the majority of these loci we identified both promoter regions and transcription termination signals characteristic for pol-III transcripts. Sequence and structure comparison with known RNA families revealed that sbRNAs are homologs of vertebrate Y RNAs. Most of the sbRNAs show the characteristic Ro protein binding motif, and contain a region highly similar to a functionally required motif for DNA replication previously thought to be unique to vertebrate Y RNAs. The single Y RNA that was previously described in C. elegans, however, does not show this motif, and in general bears the hallmarks of a highly derived family member.

Mutations in ribosomal proteins RPS19, RPS24 and RPS17 have been reported in DiamondBlackfan Anemia (DBA), an autosomal dominant disease characterised by pure red cell aplasia. DBA is the prototype of ribosomapathies: a protein synthesis defect in a tissue with a high cellular turnover is considered the cause of the erythroid progenitor failure. We have created the Diamond-Blackfan Anemia mutation database to curate and record DBA gene mutations, together with their functional consequences and clinical phenotypes. This locusspecific resource is open to future submissions and is available online (http://www.dbagenes.unito.it). It is founded on the Leiden Open (source) Variation Database (LOVD) system and includes data from sequence and structure analysis tools, genomic database resources and published reports. It lists all identified variants and background genomic information. Phenotypic data are accessed by selecting a particular mutation. The database includes 219 unique variants of which 86 are disease-causing mutations. The database will be supplemented with other DBA genes as soon as they are reported and their mutations are identified and it should be of assistance to clinicians and investigators involved in DBA research and care.© 2008 Wiley-Liss, Inc.KEY WORDS: Diamond-Blackfan Anemia, ribosomal protein, erythropoiesis, ribosome biogenesis. INTRODUCTIONDiamond-Blackfan anemia (DBA; MIM# 105650) is a pure red cell aplasia of childhood with an incidence ranging from 5 to 10 cases per million live births in Europe [Campagnoli et al., 2004]. Its main clinical features are normochromic and macrocytic anemia, reticulocytopenia and hypoplasia of erythroid progenitors in the bone marrow, whereas other hematopoietic lineages are usually normal [Campagnoli et al., 2004]. About 30% of patients display somatic abnormalities, involving the upper limbs, head, neck, the urogenital and cardiovascular systems, along with growth retardation. Patients have an increased risk of malignancies [Campagnoli et al., 2004;Lipton et al., 2001]. Management begins with corticosteroids, though the response is variable. Non-responders require multiple blood transfusions. Allogeneic bone marrow or stem cells transplantation is the only curative treatment at present [Roy et al., 2005;Lipton et al., 2006].Ribosomal protein (RP) S19 was the only gene associated with DBA for several years. It is mutated in 25% of patients with either sporadic or familial DBA, always in heterozygosity [Draptchinskaia et al., 1999;Campagnoli et al., 2008]. Mutations in RPS24 have been identified in 3/215 (~2%) DBA probands [Gazda et al., 2006] RPS17 mutation was reported in 1/24 [Cmejla et al., 2007]. Mutations in RPL35A [Farrar et al., 2007], RPL11 and RPL5 have been described, but not yet published in extenso. DBA is thus the only known human disease caused by an RP deficiency and is the prototype of ribosomapathies [Luzzatto and Karadimitris, 1998].The RPS19 gene (MIM# 603474) maps on locus 19q13.2, comprises six exons and spans 11 kb. The first exon (3...

Defects in genes encoding ribosomal proteins cause Diamond Blackfan Anemia (DBA), a red cell aplasia often associated with physical abnormalities. Other bone marrow failure syndromes have been attributed to defects in ribosomal components but the link between erythropoiesis and the ribosome remains to be fully defined. Several lines of evidence suggest that defects in ribosome synthesis lead to “ribosomal stress” with p53 activation and either cell cycle arrest or induction of apoptosis. Pathways independent of p53 have also been proposed to play a role in DBA pathogenesis.We took an unbiased approach to identify p53-independent pathways activated by defects in ribosome synthesis by analyzing global gene expression in various cellular models of DBA. Ranking-Principal Component Analysis (Ranking-PCA) was applied to the identified datasets to determine whether there are common sets of genes whose expression is altered in these different cellular models. We observed consistent changes in the expression of genes involved in cellular amino acid metabolic process, negative regulation of cell proliferation and cell redox homeostasis.These data indicate that cells respond to defects in ribosome synthesis by changing the level of expression of a limited subset of genes involved in critical cellular processes. Moreover, our data support a role for p53-independent pathways in the pathophysiology of DBA.