Diamond-Blackfan anemia, the archetype of ribosomopathy: How distinct is it from the other constitutional ribosomopathies?

Diamond-Blackfan anemia (DBA) was the first ribosomopathy described in humans. DBA is a congenital hypoplastic anemia, characterized by macrocytic aregenerative anemia, manifesting by differentiation blockage between the BFU-e/CFU-e developmental erythroid progenitor stages. In 50 % of the DBA cases, various malformations are noted. Strikingly, for a hematological disease with a relative erythroid tropism, DBA is due to ribosomal haploinsufficiency in 24 different ribosomal protein (RP) genes. A few other genes have been described in DBA-like disorders, but they do not fit into the classical DBA phenotype (Sankaran et al., 2012; van Dooijeweert et al., 2022; Toki et al., 2018; Kim et al., 2017 [1-4]). Haploinsufficiency in a RP gene leads to defective ribosomal RNA (rRNA) maturation, which is a hallmark of DBA. However, the mechanistic understandings of the erythroid tropism defect in DBA are still to be fully defined. Erythroid defect in DBA has been recently been linked in a non-exclusive manner to a number of mechanisms that include: 1) a defect in translation, in particular for the GATA1 erythroid gene; 2) a deficit of HSP70, the GATA1 chaperone, and 3) free heme toxicity. In addition, p53 activation in response to ribosomal stress is involved in DBA pathophysiology. The DBA phenotype may thus result from the combined contributions of various actors, which may explain the heterogenous phenotypes observed in DBA patients, even within the same family.

Transient erythroblastopenia due to a GATA1 variant in an infant female.

Diamond-Blackfan anemia (DBA) is a congenital anemia with erythroid cell aplasia. Most of the causative genes are ribosomal proteins. GATA1, a hematopoietic master transcription factor required for erythropoiesis, also causes DBA. GATA1 is located on Xp11.23; therefore, DBA develops only in males in an X-linked inheritance pattern. Here, we report a case of transient erythroblastopenia and moderate anemia in a female newborn infant with a de novo GATA1 variant. In this patient, increased methylation of the GATA1 wild-type allele was observed in erythroid cells. Skewed lyonization of GATA1 may cause mild transient erythroblastopenia in a female patient.

Biallelic variation in the choline and ethanolamine transporter FLVCR1 underlies a pleiotropic disease spectrum from adult neurodegeneration to severe developmental disorders.

FLVCR1 encodes Feline leukemia virus subgroup C receptor 1 (FLVCR1), a solute carrier (SLC) transporter within the Major Facilitator Superfamily. FLVCR1 is a widely expressed transmembrane protein with plasma membrane and mitochondrial isoforms implicated in heme, choline, and ethanolamine transport. While Flvcr1 knockout mice die in utero with skeletal malformations and defective erythropoiesis reminiscent of Diamond-Blackfan anemia, rare biallelic pathogenic FLVCR1 variants are linked to childhood or adult-onset neurodegeneration of the retina, spinal cord, and peripheral nervous system. We ascertained from research and clinical exome sequencing 27 individuals from 20 unrelated families with biallelic ultra-rare missense and predicted loss-of-function (pLoF) FLVCR1 variant alleles. We characterize an expansive FLVCR1 phenotypic spectrum ranging from adult-onset retinitis pigmentosa to severe developmental disorders with microcephaly, reduced brain volume, epilepsy, spasticity, and premature death. The most severely affected individuals, including three individuals with homozygous pLoF variants, share traits with Flvcr1 knockout mice and Diamond-Blackfan anemia including macrocytic anemia and congenital skeletal malformations. Pathogenic FLVCR1 missense variants primarily lie within transmembrane domains and reduce choline and ethanolamine transport activity compared with wild-type FLVCR1 with minimal impact on FLVCR1 stability or subcellular localization. Several variants disrupt splicing in a mini-gene assay which may contribute to genotype-phenotype correlations. Taken together, these data support an allele-specific gene dosage model in which phenotypic severity reflects residual FLVCR1 activity. This study expands our understanding of Mendelian disorders of choline and ethanolamine transport and demonstrates the importance of choline and ethanolamine in neurodevelopment and neuronal homeostasis.

The Paradox of Ribosomal Insufficiency Coupled with Increased Cancer: Shifting the Perspective from the Cancer Cell to the Microenvironment.

Ribosomopathies are defined as inherited diseases in which ribosomal factors are mutated. In general, they present multiorgan symptoms. In spite of the fact that in cellular models, ribosomal insufficiency leads to a reduced rate of oncogenic transformation, patients affected by ribosomopathies present a paradoxical increase in cancer incidence. Several hypotheses that explain this paradox have been formulated, mostly on the assumption that altered ribosomes in a stem cell induce compensatory changes that lead to a cancer cell. For instance, the lack of a specific ribosomal protein can lead to the generation of an abnormal ribosome, an oncoribosome, that itself leads to altered translation and increased tumorigenesis. Alternatively, the presence of ribosomal stress may induce compensatory proliferation that in turns selects the loss of tumor suppressors such as p53. However, modern views on cancer have shifted the focus from the cancer cell to the tumor microenvironment. In particular, it is evident that human lymphocytes are able to eliminate mutant cells and contribute to the maintenance of cancer-free tissues. Indeed, many tumors develop in conditions of reduced immune surveillance. In this review, we summarize the current evidence and attempt to explain cancer and ribosomopathies from the perspective of the microenvironment.

Towards a Cure for Diamond-Blackfan Anemia: Views on Gene Therapy.

Diamond-Blackfan anemia (DBA) is a rare genetic disorder affecting the bone marrow's ability to produce red blood cells, leading to severe anemia and various physical abnormalities. Approximately 75% of DBA cases involve heterozygous mutations in ribosomal protein (RP) genes, classifying it as a ribosomopathy, with RPS19 being the most frequently mutated gene. Non-RP mutations, such as in GATA1, have also been identified. Current treatments include glucocorticosteroids, blood transfusions, and hematopoietic stem cell transplantation (HSCT), with HSCT being the only curative option, albeit with challenges like donor availability and immunological complications. Gene therapy, particularly using lentiviral vectors and CRISPR/Cas9 technology, emerges as a promising alternative. This review explores the potential of gene therapy, focusing on lentiviral vectors and CRISPR/Cas9 technology in combination with non-integrating lentiviral vectors, as a curative solution for DBA. It highlights the transformative advancements in the treatment landscape of DBA, offering hope for individuals affected by this condition.

Inherited bone marrow failure syndromes: phenotype as a tool for early diagnostic suspicion at a major reference center in Mexico.

Introduction: The inherited bone marrow failure syndromes (IBMFSs) are a group of rare disorders characterized by bone marrow failure (BMF), physical abnormalities, and an increased risk of neoplasia. The National Institute of Pediatrics (INP) is a major medical institution in Mexico, where patients with BMF receive a complete approach that includes paraclinical tests. Readily recognizable features, such as the hematological and distinctive physical phenotypes, identified by clinical dysmorphologists, remain crucial for the diagnosis and management of these patients, particularly in circumstances where next-generation sequencing (NGS) is not easily available. Here, we describe a group of Mexican patients with a high clinical suspicion of an IBMFS. Methods: We performed a systematic retrospective analysis of the medical records of patients who had a high IBMFS suspicion at our institution from January 2018 to July 2021. An initial assessment included first ruling out acquired causes of BMF by the Hematology Department and referral of the patient to the Department of Human Genetics for physical examination to search for specific phenotypes suggesting an IBMFS. Patients with high suspicion of having an IBMFS were classified into two main groups: 1) specific IBMFS, including dyskeratosis congenita (DC), Diamond-Blackfan anemia (DBA), Shwachman-Diamond syndrome (SDS), thrombocytopenia with absent radii (TAR), and severe congenital neutropenia (SCN); 2) undefined IBMFS (UI). Results: We established a high suspicion of having an IBMFS in 48 patients. At initial evaluation, the most common hematologic features were bicytopenia (20%) and aplastic anemia (16%); three patients received hematopoietic stem cell transplantation. Among patients with a suspicion of an IBMFS, the most common physical abnormality was minor craniofacial features in 83% of patients and neurodevelopmental disorders in 52%. The specific suspicions that we built were DBA (31%), SDS (18%), DC (14%), TAR (4%), and SCN (4%), whereas 27% of cases remained as undefined IBMFS. SDS, TAR, and SCN were more commonly suspected at an earlier age (<1 year), followed by DBA (2 years) and DC (5 years). Conclusions: Thorough examination of reported clinical data allowed us to highly suspect a specific IBMFS in approximately 70% of patients; however, an important number of patients remained with suspicion of an undefined IBMFS. Implementation of NGS and telomere length measurement are forthcoming measures to improve IBMFS diagnosis in Mexico.

Aplasia medular congénita de serie roja: Anemia de DiamondBlackfan. A propósito de un caso / Marrow aplasia congenital red series: Diamond BlackfanAnemia. About a case

La Aplasia Medular pura de Células Rojas es un trastorno que se caracteriza por anemia con ausencia casi completa de precursores de células rojas en la médula ósea, con contaje de leucocitos y plaquetas normales. La anemia de Diamond-Blackfan es un síndrome de insuficiencia de la médula ósea caracterizada por anemia, reticulocitopenia y disminución de precursores eritroides en la médula ósea. Se presenta el caso de un lactante menor masculino de 2 meses de edad, sin antecedentes familiares ni perinatales de importancia, cuya madre evidencia palidez cutáneo mucosa progresiva asociado a hiporexia; acude a centro de salud donde realizan paraclínicos que reportan hemoglobina en 1,7g/dL. Se realiza frotis de sangre periférica donde se muestra serie eritroide francamente afectada con contaje granulocítico y megacariocítico normales; se realiza biopsia y aspirado de médula ósea concluyéndose aplasia medular de serie roja y en vista de otros hallazgos clínicos, se plantea posible anemia de Diamond-lackfan. Se indica tratamiento con glucocorticoides, sin embargo por respuesta insuficiente, se inicia eritropoyetina aumentando dosis de forma progresiva, a pesar de la administración de la misma, amerita transfusiones sanguíneas de forma regular; se realizan estudios de compatibilidad con familiares de primer grado resultando positivos, actualmente es candidato a trasplante alogénico de médula ósea. Se concluye que a pesar de corresponder a un síndrome poco frecuente, debe sospecharse ante la presencia de anemia severa, sin pérdida sanguínea aguda y descarte previo de otras etiologías, además se plantea que el inicio oportuno del tratamiento es fundamental para la supervivencia de estos pacientes(AU)

Pure red cell aplasia medullary is a disorder characterized by anemia with almost complete absence of red cell precursors in the bone marrow, with leukocyte count and platelets. e Diamond-Blackfan anemia is a failure syndrome characterized by bone marrow anemia, reticulocytopenia and decreased erythroid precursors in the bone marrow. the case of an infant under 2 months of age presented no family or perinatal history major, whose mother progressive skin pallor evidence mucosa associated with hyporexia; go to health center where they perform paraclinical reporting hemoglobin 1.7 g /dL. peripheral blood smear where erythroid frankly affected with normal megakaryocytic granulocytic count shown is made; It biopsied and bone marrow aspirate concluding marrow red cell aplasia; possible anemia Diamond-Blackfan in light of other clinical findings arises. It stays with glucocorticoid treatment, however insufficient response, begins erythropoietin dose progressively increasing, despite it, warrants blood transfusions on a regular basis; compatibility studies performed with firstdegree resulting positive, currently a candidate for allogeneic bone marrow transplantation. It is concluded that despite being a rare syndrome should be suspected in severe anemia where there is acute blood loss, ruling out other etiologies; also timely initiation of treatment is critical to the survival of these patients(AU)

Síndrome de Pearson en un niño trasplantado debido a anemia de Diamond-Blackfan / Pearson syndrome in a child transplanted for Diamond-Blackfan anemia

El síndrome de Pearson (SP) comparte varias características con la anemia de Diamond-Blackfan (ADB), incluida la anemia grave de inicio temprano, por lo que es importante hacer un diagnóstico diferencial. El diagnóstico diferencial de la ADB y el SP es fundamental, ya que los pacientes con ADB podrían res-ponder al tratamiento con corticoesteroides, presentar remisión o beneficiarse del trasplante de células madre hematopoyéti-cas (TCMH). Sin embargo, los pacientes con SP tienen un pronós-tico diferente, con un riesgo muy elevado de acidosis, problemas metabólicos y disfunción pancreática, y una expectativa de vida menor en comparación con aquellos con ADB. En este artículo, presentamos el caso de un paciente sometido a TCMH para la ADB, pero que luego fue diagnosticado con SP tras desarrollar algunas complicaciones.

Pearson syndrome (PS), shares a number of overlapping features with Diamond-Blackfan anemia (DBA), including early onset of severe anemia, making differential diagnosis important. Differential diagnosis of DBA and PS is critical, since those with DBA may respond to treatment with steroids, may undergo remission, or may benefit from hematopoietic stem cell transplantation (HSCT). However, patients with PS have a different prognosis, with a very high risk of developing acidosis, metabolic problems, and pancreatic dysfunction, and a shorter life expectancy than those with DBA. Here we present a patient who underwent HSCT for DBA but was subsequently diagnosed with PS after developing some complications