A dominant mutation in the gene encoding the erythroid transcription factor KLF1 causes a congenital dyserythropoietic anemia.

The congenital dyserythropoietic anemias (CDAs) are inherited red blood cell disorders whose hallmarks are ineffective erythropoiesis, hemolysis, and morphological abnormalities of erythroblasts in bone marrow. We have identified a missense mutation in KLF1 of patients with a hitherto unclassified CDA. KLF1 is an erythroid transcription factor, and extensive studies in mouse models have shown that it plays a critical role in the expression of globin genes, but also in the expression of a wide spectrum of genes potentially essential for erythropoiesis. The unique features of this CDA confirm the key role of KLF1 during human erythroid differentiation. Furthermore, we show that the mutation has a dominant-negative effect on KLF1 transcriptional activity and unexpectedly abolishes the expression of the water channel AQP1 and the adhesion molecule CD44. Thus, the study of this disease-causing mutation in KLF1 provides further insights into the roles of this transcription factor during erythropoiesis in humans.

Disorders of sex development and Diamond-Blackfan anemia: is there an association?

Diamond-Blackfan anemia (DBA) is a rare disorder characterized by congenital pure red cell aplasia. Mutations in ribosomal protein S19 (RPS19) have been identified in 25% of DBA patients. More recently, mutations in other ribosomal protein genes, namely RPS7, RPS15, RPS24, RPS17, RPS27A, RPL35a, RPL36, RPL11, and RPL5, have also been found in patients with DBA. Approximately 30-40% of affected patients have various associated physical anomalies, mostly craniofacial and at the extremities, but also cardiac or urogenital malformations. Anomalies of the urogenital tract in DBA patients comprise changes in the kidney (dysplasia, agenesis, duplication, horseshoe kidney) and genitalia (hypospadias). To date, disorders of sex development (DSD) have only been described once in association with DBA. We report here four DBA patients who exhibited DSD.

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.

Role of the interaction between Lu/BCAM and the spectrin-based membrane skeleton in the increased adhesion of hereditary spherocytosis red cells to laminin.

Lu/BCAM, the unique erythroid receptor for laminin 511/521, interacts with the erythrocyte membrane skeleton through spectrin binding. It has been reported that Hereditary Spherocytosis red blood cells (HS RBC) exhibit increased adhesion to laminin. We investigated the role of Lu/BCAM-spectrin interaction in the RBC adhesion properties of 2 splenectomised HS patients characterized by 40% spectrin deficiency. Under physiological flow conditions, HS RBC exhibited an exaggerated adhesion to laminin that was completely abolished by soluble Lu/BCAM. Triton extraction experiments revealed that a greater fraction of Lu/BCAM was unlinked to the membrane skeleton of HS RBC, as compared to normal RBC. Disruption of the spectrin interaction site in Lu/BCAM expressed in the transfected K562 cell line resulted in a weakened interaction to the skeleton and an enhanced interaction to laminin. These results demonstrated that the adhesion of HS RBC to laminin was mediated by Lu/BCAM and that its interaction with the spectrin-based skeleton negatively regulated cell adhesion to laminin. Finally, the results of this study strongly suggest that the reinforced adhesiveness of spectrin-deficient HS RBC to laminin is partly brought about by an impaired interaction between Lu/BCAM and the membrane skeleton.

[Diamond-Blackfan anemia reveals the dark side of ribosome biogenesis]. / Anémie de Diamond-Blackfan: le côté obscur de la biogenèse des ribosomes.

Diamond-Blackfan anemia (DBA), a rare congenital erythroblastopenia, has recently become a paradigm for a growing set of genetic diseases linked to mutations in genes encoding ribosomal proteins or factors involved in ribosome biogenesis. Recent studies of the structure and the function of ribosomal proteins affected in DBA indicate that their mutation in DBA primarily impacts ribosome biogenesis. Accordingly, cells from DBA patients display anomalies in the maturation of ribosomal RNAs. The explanation of this unexpected link between ribosome biogenesis, a ubiquitous process, and a disease mostly affecting erythroid differentiation may stem in part from the emerging concept of ribosomal stress response, a signaling pathway triggering cell cycle arrest in response to a defect in ribosome synthesis. Future studies of DBA and other diseases related to defects in ribosome biogenesis are likely to rapidly provide important insights into the regulatory mechanisms linking cell cycle progression to this major metabolic pathway.

Study of the effects of proteasome inhibitors on ribosomal protein S19 (RPS19) mutants, identified in patients with Diamond-Blackfan anemia.

BACKGROUND: Mutations in the ribosomal protein S19 gene (RPS19) have been found in 25% of patients with Diamond-Blackfan anemia, a rare syndrome of congenital bone marrow failure characterized by erythroblastopenia and various malformations. Mechanistic understanding of the role of RPS19 in normal erythropoiesis and in the Diamond-Blackfan anemia defect is still poor. However, defective ribosome biogenesis and, in particular, impaired 18S ribosomal RNA maturation have been documented in association with various identified RPS19 mutations. Recently, new genes, all encoding ribosomal proteins, have been found to be mutated in Diamond-Blackfan anemia, adding further support to the concept that ribosome biogenesis plays an important role in regulating erythropoiesis. We previously showed variability in the levels of expression and subcellular localization of a subset of RPS19 mutant proteins. DESIGN AND METHODS: To define the mechanistic basis for this variability better, we studied a large number of mutant proteins and characterized both RPS19 expression level using a specific antibody against RPS19 and RPS19 subcellular localization after transfection of Cos-7 cells with various green fluorescent protein-RPS19 mutants. To investigate the role of the proteasome in RPS19 degradation, we examined the effect of various proteasome inhibitors, namely lactacystin, MG132, and bortezomib on RPS19 expression and subcellular localization RESULTS: We found two distinct classes of RPS19 protein defects in Diamond-Blackfan anemia based on the stability of the mutant proteins: (i) slightly decreased to normal levels of expression and normal nucleolar localization and (ii) markedly deficient expression and failure to localize to the nucleolus. All the proteasome inhibitors tested were able to restore the expression levels and normal subcellular localization of several unstable mutant proteins. CONCLUSIONS: Our findings demonstrate an important role for the proteasomal degradation pathway in regulating the expression levels and nucleolar localization of certain mutant RPS19 proteins in Diamond-Blackfan anemia.

Band 3 Courcouronnes (Ser667Phe): a trafficking mutant differentially rescued by wild-type band 3 and glycophorin A.

We describe a mutation in human erythrocyte band 3 (anion exchanger 1; SLC4A1) causing both hereditary spherocytosis and distal renal tubular acidosis. The proband developed a transfusion-dependent, hemolytic anemia following birth. Immunoblotting showed band 3 was reduced to approximately 35% of wildtype; other proteins of the band 3/Rh macrocomplex were also reduced. DNA sequence analysis revealed a novel homozygous mutation, c.2000C>T, leading to the amino acid substitution Ser667Phe. The parents were heterozygous for the same mutation. Sulfate influx in the patient's erythrocytes was approximately 40% wild type. The mutant band 3 produced very little chloride influx when expressed in Xenopus oocytes. Influx was partially rescued by coexpression of glycophorin A and also rescued by coexpression of wild-type band 3. At 2 years of age, an ammonium chloride challenge showed the child has incomplete distal renal tubular acidosis (dRTA). Stable expression of mutant kidney band 3 in both nonpolarized and polarized Madin-Darby canine kidney cells showed that most of the mutant protein was retained in the endoplasmic reticulum. Overall our results suggest that the Ser667Phe does not affect the anion transport function of band 3, but causes a trafficking defect in both erythrocytes and kidney cells.

Association between myeloid malignancies and acquired deficit in protein 4.1R: a retrospective analysis of six patients.

Constitutional deficit in the erythroid protein 4.1 (4.1R), a structural component of the erythrocyte membrane, is implicated in hereditary elliptocytosis. Acquired deficit in protein 4.1R have been rarely described in myelodysplastic syndromes. Here, we report a series of six patients presenting a myelodysplastic or a myeloproliferative disease in association with an elliptocytosis curve on osmotic gradient ektacytometry and a significant decrease in protein 4.1R level. We confirm that deficit in protein 4.1R is recurrent in myeloid malignancies and should be particularly investigated when deletion del (20 q) is present, since we found this chromosomal abnormality in four out of six patients.

[A center in Paris for screening and counselling sickle cell patients and carriers]. / Centre d'information et de dépistage de la drépanocytose a Paris.

Prevention of sickle cell anemia, a severe and painful disease, relies on carrier detection and information, and on prenatal diagnosis with the possibility of medical abortion. Here we report the first results of a medical and welfare program launched in Paris 20 months ago and dedicated to sickle cell carrier screening and information.

Detection of 28 novel mutations in the Wiskott-Aldrich syndrome and X-linked thrombocytopenia based on multiplex PCR.

The Wiskott-Aldrich syndrome (WAS) is an X-linked disorder including microthrombocytopenia, eczema and immunodeficiency. A mild form is known as the X-linked thrombocytopenia (XLT). We screened 150 individuals or families based on a multiplex PCR method. We found 28 novel mutations (7 missense, 1 nonsense, 1 nonstop change, 5 splice site mutations and 14 deletions or insertions). The method relied on the co-synthesis of 5 amplicons and direct sequencing, optimizing the novel protocol proposed by Jones et al. [L.N. Jones, M.I. Lutskiy, J. Cooley, et al. A novel protocol to identify mutations in patients with Wiskott-Aldrich syndrome, Blood Cells Mol. Dis. 28 (2002) 392-398]. It was thus possible to identify faster and at a lower cost the mutations in newly diagnosed patients. The mutation distribution, according to the type, was in keeping with the distribution reported previously. No clear-cut genotype-phenotype correlation was observed.

Dehydrated hereditary stomatocytosis mimicking familial hyperkalaemic hypertension: clinical and genetic investigation.

Dehydrated hereditary stomatocytosis (DHS) is a rare dominant form of hereditary haemolytic anaemia. In some families, pseudohyperkalaemia accompanies DHS. Familial hyperkalaemic hypertension (FHHt), a rare autosomal dominant form of arterial hypertension, is associated with genuine hyperkalaemia. We present a large French family in which DHS and FHHt were diagnosed independently in two separate branches. In branch A, mild DHS accompanied by pseudohyperkalaemia was found. In branch B, the proband and her daughter were initially diagnosed with FHHt, based on the coincidence of high blood pressure and hyperkalaemia. After finding out that branches A and B were related, reinvestigation of the affected members of branch B lead to the diagnosis of DHS, yielding the largest DHS kindred known in France. This allowed extensive linkage analysis based on 19 microsatellites markers in 12 affected and 10 unaffected members at 16q24.1qter, where one known DHS locus maps to. A maximal two-point LOD score (4.71 at theta = 0) was obtained for markers D16S3074 and D16S476. Haplotype analysis led to the definition of a new 11.5 cM disease interval with an upper limit at microsatellite D16S3037.

Impaired ribosome biogenesis in Diamond-Blackfan anemia.

The gene encoding the ribosomal protein S19 (RPS19) is frequently mutated in Diamond-Blackfan anemia (DBA), a congenital erythroblastopenia. The consequence of these mutations on the onset of the disease remains obscure. Here, we show that RPS19 plays an essential role in biogenesis of the 40S small ribosomal subunit in human cells. Knockdown of RPS19 expression by siRNAs impairs 18S rRNA synthesis and formation of 40S subunits and induces apoptosis in HeLa cells. Pre-rRNA processing is altered, which leads to an arrest in the maturation of precursors to the 18S rRNA. Under these conditions, pre-40S particles are not exported to the cytoplasm and accumulate in the nucleoplasm of the cells in perinuclear dots. Consistently, we find that ribosome biogenesis and nucleolar organization is altered in skin fibroblasts from DBA patients bearing mutations in the RPS19 gene. In addition, maturation of the 18S rRNA is also perturbed in cells from a patient bearing no RPS19-related mutation. These results support the hypothesis that DBA is directly related to a defect in ribosome biogenesis and indicate that yet to be discovered DBA-related genes may be involved in the synthesis of the ribosomal subunits.

Ribosomal protein S24 gene is mutated in Diamond-Blackfan anemia.

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.

Incidence of hereditary spherocytosis in a population of jaundiced neonates.

As most of hereditary spherocytosis-affected individuals experience jaundice at birth, it seemed of interest to evaluate the proportion of hereditary spherocytosis in 402 severely jaundiced neonates with a bilirubinemia level prompting phototherapy. Red cell dehydration, a hallmark of spherocytosis whether constitutional or acquired, was demonstrated in 74 of them, among whom 23 disclosed a typical pattern of spherocytosis upon red cell deformability studies. Acquired spherocytosis of immune origin was diagnosed in 19/23 and hereditary spherocytosis in 4, making the proportion of hereditary spherocytosis-affected individuals among a severely jaundiced population of neonates amount to 1%, an incidence at least 30-fold that of the overall population.

High-risk pregnancies in Diamond-Blackfan anemia: a survey of 64 pregnancies from the French and German registries.

We reviewed 64 pregnancies in 26 women with Diamond-Blackfan anemia (DBA) included in the French and German DBA registries. Complications were seen in 42 pregnancies (66%) and included abortion, pre-eclampsia, in utero fetal death, intrauterine growth retardation, retroplacental hematoma, pre-term delivery and fetal malformations. Of the 34 children (53%) born alive, 13 had DBA. No correlations were found between pregnancy outcome and features of either maternal or child DBA. Pregnancies in DBA-affected women are at high risk, especially for complications likely to be of vascular-placental origin. Careful monitoring with prevention of severe anemia and early introduction of aspirin is suggested.

Two new human DMT1 gene mutations in a patient with microcytic anemia, low ferritinemia, and liver iron overload.

DMT1 mediates the pH-dependent uptake of Fe(2+) from the diet in duodenal enterocytes and in most other cells. It transfers iron from the endosomes to the cytosol following the uptake of the transferrin-transferrin receptor complex. DMT1 mutations are responsible for severe hypochromic microcytic anemia in rodents and in 2 human patients described recently. We report a compound heterozygote for 2 new DMT1 mutations, associated with microcytic anemia from birth and progressive liver iron overload. The first mutation is a GTG deletion in exon 5, leading to the V114 in-frame deletion in transmembrane domain 2, and the second is a G --> T substitution in exon 8 leading to the G212V replacement in transmembrane domain 5. Together with the 2 previously reported cases, this patient defines a new syndrome of congenital microcytic hypochromic anemia, poorly responsive to oral iron treatment, with liver iron overload associated paradoxically with normal to moderately elevated serum ferritin levels.

Parvovirus B19-induced anemia in renal transplantation: a role for rHuEPO in resistance to classical treatment.

Human parvovirus B19 (PVB 19) is responsible for pure red cell aplasia in immunocompromised patients, and particularly solid organ recipients. Intravenous immunoglobulins (IVIG) have been shown to be efficient to achieve the correction of anemia in association with the reduction of immunosuppression. We report a case of kidney transplant recipient with PVB 19-induced anemia that did not respond to recombinant human erythropoietin (rHuEPO) and to a first course of IVIG. After discontinuation of rHuEPO, a second course of IVIG was successful with the resolution of anemia. We discuss the role of rHuEPO that may facilitate PVB 19 replication in erythropoietin-sensitive human erythroid progenitor cells.