Loss of function mutations in RPL27 and RPS27 identified by whole‐exome sequencing in Diamond‐Blackfan anaemia

Diamond‐Blackfan anaemia is a congenital bone marrow failure syndrome that is characterized by red blood cell aplasia. The disease has been associated with mutations or large deletions in 11 ribosomal protein genes including RPS7, RPS10, RPS17, RPS19, RPS24, RPS26, RPS29, RPL5, RPL11, RPL26 and RPL35A as well as GATA1 in more than 50% of patients. However, the molecular aetiology of many Diamond‐Blackfan anaemia cases remains to be uncovered. To identify new mutations responsible for Diamond‐Blackfan anaemia, we performed whole‐exome sequencing analysis of 48 patients with no documented mutations/deletions involving known Diamond‐Blackfan anaemia genes except for RPS7, RPL26, RPS29 and GATA1. Here, we identified a de novo splicing error mutation in RPL27 and frameshift deletion in RPS27 in sporadic patients with Diamond‐Blackfan anaemia. In vitro knockdown of gene expression disturbed pre‐ribosomal RNA processing. Zebrafish models of rpl27 and rps27 mutations showed impairments of erythrocyte production and tail and/or brain development. Additional novel mutations were found in eight patients, including RPL3L, RPL6, RPL7L1T, RPL8, RPL13, RPL14, RPL18A and RPL31. In conclusion, we identified novel germline mutations of two ribosomal protein genes responsible for Diamond‐Blackfan anaemia, further confirming the concept that mutations in ribosomal protein genes lead to Diamond‐Blackfan anaemia.     

Diagnosing and treating Diamond Blackfan anaemia: results of an international clinical consensus conference

Diamond Blackfan anaemia (DBA) is a rare, genetically and clinically heterogeneous, inherited red cell aplasia. Classical DBA affects about seven per million live births and presents during the first year of life. However, as mutated genes have been discovered in DBA, non-classical cases with less distinct phenotypes are being described in adults as well as children. In caring for these patients it is often difficult to have a clear understanding of the treatment options and their outcomes because of the lack of complete information on the natural history of the disease. The purpose of this document is to review the criteria for diagnosis, evaluate the available treatment options, including corticosteroid and transfusion therapies and stem cell transplantation, and propose a plan for optimizing patient care. Congenital anomalies, mode of inheritance, cancer predisposition, and pregnancy in DBA are also reviewed. Evidence-based conclusions will be made when possible; however, as in many rare diseases, the data are often anecdotal and the recommendations are based upon the best judgment of experienced clinicians. The recommendations regarding the diagnosis and management described in this report are the result of deliberations and discussions at an international consensus conference.     

Ribosomal RNA analysis in the diagnosis of Diamond‐Blackfan Anaemia

Diamond‐Blackfan anaemia (DBA) is an inherited disease characterized by pure erythroid aplasia that has been tagged as a ‘ribosomopathy’. We report a multi‐centre study focused on the analysis of rRNA processing of 53 Italian DBA patients using capillary electrophoresis analysis of rRNA maturation of the 40S and 60S ribosomal subunits. The ratio of 28S/18S rRNA was higher in patients with mutated ribosomal proteins (RPs) of the small ribosomal subunit. In contrast, patients with mutated RPs of the large ribosomal subunit (RPLs) had a lower 28S/18S ratio. The assay reported here would be amenable for development as a diagnostic tool.     

Target enrichment and high‐throughput sequencing of 80 ribosomal protein genes to identify mutations associated with Diamond‐Blackfan anaemia

Diamond‐Blackfan anaemia (DBA) is caused by inactivating mutations in ribosomal protein (RP) genes, with mutations in 13 of the 80 RP genes accounting for 50–60% of cases. The remaining 40–50% cases may harbour mutations in one of the remaining RP genes, but the very low frequencies render conventional genetic screening as challenging. We, therefore, applied custom enrichment technology combined with high‐throughput sequencing to screen all 80 RP genes. Using this approach, we identified and validated inactivating mutations in 15/17 (88%) DBA patients. Target enrichment combined with high‐throughput sequencing is a robust and improved methodology for the genetic diagnosis of DBA.     

Glucocorticoids improve erythroid progenitor maintenance and dampen Trp53 response in a mouse model of Diamond–Blackfan anaemia

Diamond–Blackfan anaemia (DBA) is a rare congenital disease causing severe anaemia and progressive bone marrow failure. The majority of patients carry mutations in ribosomal proteins, which leads to depletion of erythroid progenitors in the bone marrow. As many as 40% of all DBA patients receive glucocorticoids to alleviate their anaemia. However, despite their use in DBA treatment for more than half a century, the therapeutic mechanisms of glucocorticoids remain largely unknown. Therefore we sought to study disease specific effects of glucocorticoid treatment using a ribosomal protein s19 (Rps19) deficient mouse model of DBA. This study determines for the first time that a mouse model of DBA can respond to glucocorticoid treatment, similar to DBA patients. Our results demonstrate that glucocorticoid treatment reduces apoptosis, rescues erythroid progenitor depletion and premature differentiation of erythroid cells. Furthermore, glucocorticoids prevent Trp53 activation in Rps19‐deficient cells‐ in a disease‐specific manner. Dissecting the therapeutic mechanisms behind glucocorticoid treatment of DBA provides indispensible insight into DBA pathogenesis. Identifying mechanisms important for DBA treatment also enables development of more disease‐specific treatments of DBA.     

Diamond Blackfan anaemia in the UK: clinical and genetic heterogeneity

A 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 genomics of inherited bone marrow failure: from mechanism to the clinic

The inherited bone marrow failure syndromes (IBMFS) typically present with significant cytopenias in at least one haematopoietic cell lineage that may progress to pancytopenia, and are associated with increased risk of cancer. Although the clinical features of the IBMFS are often diagnostic, variable disease penetrance and expressivity may result in diagnostic dilemmas. The discovery of the genetic aetiology of the IBMFS has been greatly facilitated by next‐generation sequencing methods. This has advanced understanding of the underlying biology of the IBMFS and been essential in improving clinical management and genetic counselling for affected patients. Herein we review the clinical features, underlying biology, and new genomic discoveries in the IBMFS, including Fanconi anaemia, dyskeratosis congenita, Diamond Blackfan anaemia, Shwachman Diamond syndrome and some disorders of the myeloid and megakaryocytic lineages.     

Recent developments in understanding the pathogenesis of aplastic anemia.

Bone marrow failure in aplastic anemia (AA) could result from abnormalities of hematopoietic stem cells, abnormal control of hematopoiesis, or abnormalities of the hematopoietic environment. Bone marrow transplantation, in vitro marrow culture techniques, and studies in animal models of marrow failure have provided insights on the possible pathogenetic mechanisms underlying AA. Studies in man and in murine models suggest that most often AA results from injuries to hematopoietic stem cells. Despite the intriguing report of abnormal regulatory cells in congenitally anemic mice, instances of marrow failure due to defective humoral or cellular control of hematopoiesis have not been identified in man. In vitro studies employing allogeneic marrow targets have suggested that immune suppression of hematopoiesis may occasionally mediate AA in man. Marrow failure due to abnormalities of the hematopoietic microenvironment has been suggested by experience with bone marrow transplantation, but no direct study of this possibility has been reported. Based on available evidence, it seems likely that AA will prove to be many diseases that share common clinical and morphologic features.     

Pathophysiology and management of inherited bone marrow failure syndromes

The inherited marrow failure syndromes are a diverse set of genetic disorders characterized by hematopoietic aplasia and cancer predisposition. The clinical phenotypes are highly variable and much broader than previously recognized. The medical management of the inherited marrow failure syndromes differs from that of acquired aplastic anemia or malignancies arising in the general population. Diagnostic workup, molecular pathogenesis, and clinical treatment are reviewed.     

Diamond-Blackfan anemia: genotype-phenotype correlations in Italian patients with RPL5 and RPL11 mutations

Background

Diamond-Blackfan anemia is a rare, pure red blood cell aplasia of childhood due to an intrinsic defect in erythropoietic progenitors. About 40% of patients display various malformations. Anemia is corrected by steroid treatment in more than 50% of cases; non-responders need chronic transfusions or stem cell transplantation. Defects in the RPS19 gene, encoding the ribosomal protein S19, are the main known cause of Diamond-Blackfan anemia and account for more than 25% of cases. Mutations in RPS24, RPS17, and RPL35A described in a minority of patients show that Diamond-Blackfan anemia is a disorder of ribosome biogenesis. Two new genes (RPL5, RPL11), encoding for ribosomal proteins of the large subunit, have been reported to be involved in a considerable percentage of patients.

Design and Methods

In this genotype-phenotype analysis we screened the coding sequence and intron-exon boundaries of RPS14, RPS16, RPS24, RPL5, RPL11, and RPL35A in 92 Italian patients with Diamond-Blackfan anemia who were negative for RPS19 mutations.

Results

About 20% of the patients screened had mutations in RPL5 or RPL11, and only 1.6% in RPS24. All but three mutations that we report here are new mutations. No mutations were found in RPS14, RPS16, or RPL35A. Remarkably, we observed a higher percentage of somatic malformations in patients with RPL5 and RPL11 mutations. A close association was evident between RPL5 mutations and craniofacial malformations, and between hand malformations and RPL11 mutations.

Conclusions

Mutations in four ribosomal proteins account for around 50% of all cases of Diamond-Blackfan anemia in Italian patients. Genotype-phenotype data suggest that mutation screening should begin with RPL5 and RPL11 in patients with Diamond-Blackfan anemia with malformations.     

Usefulness of electron microscopy in the diagnosis of congenital dyserythropoietic anemia type I: report of a case.

This report describes a case of congenital dyserythropoietic anemia (CDA) type I diagnosed in a 22-year-old woman with a two year history of macrocytic anemia. Light microscopy study of bone marrow disclosed only minor and nonspecific findings, without erythroid hyperplasia. Electron microscopy of bone marrow erythroblasts surprisingly showed most of the classical features of CDA type I. Electron microscopy may be an important tool for the diagnosis of macrocytic anemia of obscure origin, especially in young patients.     

再生障碍性贫血的骨髓和细胞病理

目的：研究再生障碍性贫血（AA）患者骨髓组织病理及有核细胞的超微结构变化。方法：光镜观察20例AA患者骨髓活检病理,透射电镜分析骨髓有核细胞超微结构。结果：光镜下所有患者骨髓脂肪组织增多,造血面积减小,大部分存在血浆渗出、出血和纤维细胞局灶性增生,血窦血管结构紊乱。电镜观察显示原始和早幼红细胞代偿性不典型增生,中晚幼红细胞核损伤。粒细胞呈活化和损伤状态;巨核细胞显著减少,胞浆灶性坏死;单核细胞异常增生、活化、吞噬和坏死。淋巴细胞大部分结构正常。结论：AA患者骨髓造血细胞减少和炎症反应同时存在,单核巨噬细胞活化和吞噬反应与造血细胞损伤相关。     

Genetic variants in the noncoding region of RPS19 gene in Diamond‐Blackfan anemia: Potential implications for phenotypic heterogeneity

Mutations in the RPS19 gene have been identified in 25% of individuals affected by Diamond‐Blackfan anemia (DBA), a congenital erythroblastopenia characterized by an aregenerative anemia and a variety of malformations. More than 60 mutations in the five coding exons of RPS19 have been described to date. We previously reported a mutation (c.‐1 + 26G>T) and an insertion at ?631 upstream of ATG (c.‐147_‐146insGCCA) in the noncoding region. Because DBA phenotype is extremely heterogeneous from silent to severe and because haploinsufficiency seems to play a role in this process, it is likely that genetic variations in the noncoding regions affecting translation of RPS19 can modulate the phenotypic expression of DBA. However, to date, very few studies have addressed this question comprehensively. In this study, we performed detailed sequence analysis of the RPS19 gene in 239 patients with DBA and 110 of their relatives. We found that 6.2% of the patients with DBA carried allelic variations upstream of ATG: 3.3% with c.‐1 + 26G>T; 2.5% with c.‐147_‐146insGCCA; and 0.4% with c.‐174G>A. Interestingly, the c.‐147_‐146insGCCA, which has been found in a black American and French Caribbean control population, was not found in 500 Caucasian control chromosomes we studied. However, it was found in association with the same haplotype distribution of four intronic polymorphisms in our patients with DBA. Although a polymorphism, the frequency of this variant in the patients with DBA and its association with the same haplotype raises the possibility that this polymorphism and the other genetic variations in the noncoding region could play a role in DBA pathogenesis. Am. J. Hematol., 2010. © 2009 Wiley‐Liss, Inc.     

Distinct ribosome maturation defects in yeast models of Diamond-Blackfan anemia and Shwachman-Diamond syndrome

Background

Diamond-Blackfan anemia and Shwachman-Diamond syndrome are inherited bone marrow failure syndromes linked to defects in ribosome synthesis. The purpose of this study was to determine whether yeast models for Diamond-Blackfan anemia and Shwachman-Diamond syndrome differed in the mechanism by which ribosome synthesis was affected.

Design and Methods

Northern blotting, pulse-chase analysis, and polysome profiling were used to study ribosome synthesis in yeast models. Localization of 60S ribosomal subunits was assessed using RPL25eGFP.

Results

Relative to wild-type controls, each disease model showed defects in 60S subunit maturation, but with distinct underlying mechanisms. In the model of Diamond-Blackfan anemia, 60S subunit maturation was disrupted at a relatively early stage with abortive complexes subject to rapid degradation. 5S ribosomal RNA, unlike other large subunit ribosomal RNA in this model, accumulated as an extra-ribosomal species. In contrast, subunit maturation in the Shwachman-Diamond syndrome model was affected at a later step, giving rise to relatively stable pre-60S particles with associated 5S ribosomal RNA retained in the nucleus.

Conclusions

These differences between the yeast Diamond-Blackfan anemia and Shwachman-Diamond syndrome models have implications for signaling mechanisms linking abortive ribosome assembly to cell fate decisions and may contribute to the divergent clinical presentations of Diamond-Blackfan anemia and Shwachman-Diamond syndrome.     

Haematopoietic stem cell transplantation for Diamond Blackfan anaemia: a report from the Italian Association of Paediatric Haematology and Oncology Registry

Allogeneic haematopoietic stem cell transplantation (HSCT) is the only curative option for patients with Diamond Blackfan anaemia (DBA). We report the transplantation outcome of 30 Italian DBA patients referred to the Italian Association of Paediatric Haematology and Oncology Registry between 1990 and 2012. This is one of the largest national registry cohorts of transplanted DBA patients. Most patients (83%) were allografted after 2000. A matched sibling donor was employed in 16 patients (53%), the remaining 14 patients (47%) were transplanted from matched unrelated donors. Twenty‐eight of the 30 patients engrafted. One patient died at day +6 due to veno‐occlusive disease without achieving neutrophil recovery and another patient remained transfusion‐dependent despite the presence of a full donor chimerism. The 5‐year overall survival and transplant‐related mortality was 74·4% and 25·6%, respectively. Patients younger than 10 years as well as those transplanted after 2000 showed a significantly higher overall survival and a significantly lower risk of transplant‐related mortality. No difference between donor type was observed. Our data suggest that allogeneic HSCT from a related or unrelated donor was a reasonable alternative to transfusion therapy in young and well chelated DBA patients.