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X-linked sideroblastic anemia due to ALAS2 intron 1 enhancer element GATA-binding site mutations.

ABSTRACT: X-linked sideroblastic anemia (XLSA) is the most common form of congenital sideroblastic anemia. In affected males, it is uniformly associated with partial loss-of-function missense mutations in the erythroid-specific heme biosynthesis protein 5-aminolevulinate synthase 2 (ALAS2). Here, we report five families with XLSA owing to mutations in a GATA transcription factor binding site located in a transcriptional enhancer element in intron 1 of the ALAS2 gene. As such, this study defines a new class of mutations that should be evaluated in patients undergoing genetic testing for a suspected diagnosis of XLSA.

SUBMITTER: Campagna DR

PROVIDER: S-EPMC3943703 | biostudies-literature | 2014 Mar

REPOSITORIES: biostudies-literature

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X-linked sideroblastic anemia due to ALAS2 intron 1 enhancer element GATA-binding site mutations.

Campagna Dean R DR de Bie Charlotte I CI Schmitz-Abe Klaus K Sweeney Marion M Sendamarai Anoop K AK Schmidt Paul J PJ Heeney Matthew M MM Yntema Helger G HG Kannengiesser Caroline C Grandchamp Bernard B Niemeyer Charlotte M CM Knoers Nine V A M NV Swart Sonia S Marron Gordon G van Wijk Richard R Raymakers Reinier A RA May Alison A Markianos Kyriacos K Bottomley Sylvia S SS Swinkels Dorine W DW Fleming Mark D MD

American journal of hematology 20131120 3

X-linked sideroblastic anemia (XLSA) is the most common form of congenital sideroblastic anemia. In affected males, it is uniformly associated with partial loss-of-function missense mutations in the erythroid-specific heme biosynthesis protein 5-aminolevulinate synthase 2 (ALAS2). Here, we report five families with XLSA owing to mutations in a GATA transcription factor binding site located in a transcriptional enhancer element in intron 1 of the ALAS2 gene. As such, this study defines a new clas ...[more]

PMID: 24166784

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Congenital sideroblastic anemia model due to ALAS2 mutation is susceptible to ferroptosis.

Project description:X-linked sideroblastic anemia (XLSA), the most common form of congenital sideroblastic anemia, is caused by a germline mutation in the erythroid-specific 5-aminolevulinate synthase (ALAS2) gene. In XLSA, defective heme biosynthesis leads to ring sideroblast formation because of excess mitochondrial iron accumulation. In this study, we introduced ALAS2 missense mutations on human umbilical cord blood-derived erythroblasts; hereafter, we refer to them as XLSA clones. XLSA clones that differentiated into mature erythroblasts showed an increased frequency of ring sideroblast formation with impaired hemoglobin biosynthesis. The expression profiling revealed significant enrichment of genes involved in ferroptosis, which is a form of regulated cell death induced by iron accumulation and lipid peroxidation. Notably, treatment with erastin, a ferroptosis inducer, caused a higher proportion of cell death in XLSA clones. XLSA clones exhibited significantly higher levels of intracellular lipid peroxides and enhanced expression of BACH1, a regulator of iron metabolism and potential accelerator of ferroptosis. In XLSA clones, BACH1 repressed genes involved in iron metabolism and glutathione synthesis. Collectively, defective heme biosynthesis in XLSA clones could confer enhanced BACH1 expression, leading to increased susceptibility to ferroptosis. The results of our study provide important information for the development of novel therapeutic targets for XLSA.

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Intron 1 GATA site enhances ALAS2 expression indispensably during erythroid differentiation.

Project description:The first intronic mutations in the intron 1 GATA site (int-1-GATA) of 5-aminolevulinate synthase 2 (ALAS2) have been identified in X-linked sideroblastic anemia (XLSA) pedigrees, strongly suggesting it could be causal mutations of XLSA. However, the function of this int-1-GATA site during in vivo development remains largely unknown. Here, we generated mice lacking a 13 bp fragment, including this int-1-GATA site (T AGATAA: AGCCCC) and found that hemizygous deletion led to an embryonic lethal phenotype due to severe anemia resulting from a lack of ALAS2 expression, indicating that this non-coding sequence is indispensable for ALAS2 expression in vivo Further analyses revealed that this int-1-GATA site anchored the GATA site in intron 8 (int-8-GATA) and the proximal promoter, forming a long-range loop to enhance ALAS2 expression by an enhancer complex including GATA1, TAL1, LMO2, LDB1 and Pol II at least, in erythroid cells. However, compared with the int-8-GATA site, the int-1-GATA site is more essential for regulating ALAS2 expression through CRISPR/Cas9-mediated site-specific deletion. Therefore, the int-1-GATA site could serve as a valuable site for diagnosing XLSA in cases with unknown mutations.

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X-linked sideroblastic anemia due to carboxyl-terminal ALAS2 mutations that cause loss of binding to the β-subunit of succinyl-CoA synthetase (SUCLA2).

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A hemizygous p.R204Q mutation in the ALAS2 gene underlies X-linked sideroblastic anemia in an adult Chinese Han man.

Project description:BackgroundX-linked sideroblastic anemia (XLSA) is the most common form of congenital sideroblastic anemia (CSA), and is associated with the mutations in the 5-aminolevulinate synthase 2 (ALAS2). The genetic basis of more than 40% of CSA cases remains unknown.MethodsA two-generation Chinese family with XLSA was studied by next-generation sequencing to identify the underlying CSA-related mutations.ResultsIn the study, we identified a missense ALAS2 R204Q mutation in a hemizygous Chinese Han man and in his heterozygous daughter. The male proband presented clinical manifestations at 38 years old and had a good response to pyridoxine.ConclusionsXLSA, as a hereditary disease, can present clinical manifestations later in lives, for adult male patients with ringed sideroblasts and hypochromic anemia, it should be evaluated with gene analyses to exclude CSA.

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Identification of a novel erythroid-specific enhancer for the ALAS2 gene and its loss-of-function mutation which is associated with congenital sideroblastic anemia.

Project description:Erythroid-specific 5-aminolevulinate synthase (ALAS2) is the rate-limiting enzyme for heme biosynthesis in erythroid cells, and a missense mutation of the ALAS2 gene is associated with congenital sideroblastic anemia. However, the gene responsible for this form of anemia remains unclear in about 40% of patients. Here, we identify a novel erythroid-specific enhancer of 130 base pairs in the first intron of the ALAS2 gene. The newly identified enhancer contains a cis-acting element that is bound by the erythroid-specific transcription factor GATA1, as confirmed by chromatin immunoprecipitation analysis in vivo and by electrophoretic mobility shift assay in vitro. A promoter activity assay in K562 human erythroleukemia cells revealed that the presence of this 130-base pair region increased the promoter activity of the ALAS2 gene by 10-15-fold. Importantly, two mutations, each of which disrupts the GATA-binding site in the enhancer, were identified in unrelated male patients with congenital sideroblastic anemia, and the lower expression level of ALAS2 mRNA in bone marrow erythroblasts was confirmed in one of these patients. Moreover, GATA1 failed to bind to each mutant sequence at the GATA-binding site, and each mutation abolished the enhancer function on ALAS2 promoter activity in K562 cells. Thus, a mutation at the GATA-binding site in this enhancer may cause congenital sideroblastic anemia. These results suggest that the newly identified intronic enhancer is essential for the expression of the ALAS2 gene in erythroid cells. We propose that the 130-base pair enhancer region located in the first intron of the ALAS2 gene should be examined in patients with congenital sideroblastic anemia in whom the gene responsible is unknown.

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Project description:The congenital sideroblastic anemias (CSAs) are relatively uncommon diseases characterized by defects in mitochondrial heme synthesis, iron-sulfur (Fe-S) cluster biogenesis, or protein synthesis. Here we demonstrate that mutations in HSPA9, a mitochondrial HSP70 homolog located in the chromosome 5q deletion syndrome 5q33 critical deletion interval and involved in mitochondrial Fe-S biogenesis, result in CSA inherited as an autosomal recessive trait. In a fraction of patients with just 1 severe loss-of-function allele, expression of the clinical phenotype is associated with a common coding single nucleotide polymorphism in trans that correlates with reduced messenger RNA expression and results in a pseudodominant pattern of inheritance.

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Azacitidine as a potential therapeutic drug in pyridoxine-refractory female X-linked sideroblastic anemia

Project description:X-linked sideroblastic anemia (XLSA) is associated with mutations in the erythroid-specific δ-aminolevulinic acid synthase (ALAS2) gene. Apart from pyridoxine-responsive patients, treatment for XLSA is mainly supportive. Female XLSA often represents a later onset of severe anemia, mostly due to the acquired skewing of X-chromosome inactivation. We successfully generated active wild-type and active mutant ALAS2 induced pluripotent stem cell (iPSC) lines from the peripheral blood cells of an affected mother and two daughters in a family with pyridoxine-resistant XLSA due to a heterozygous ALAS2 missense mutation (R227C). The erythroid differentiation potential was severely impaired in active mutant iPSC lines compared with active wild-type iPSC lines. Most of the active mutant erythroblasts revealed an immature morphological phenotype, and some showed dysplasia and perinuclear iron deposits. Additionally, globin and HO-1 expression and heme biosynthesis in active mutant erythroblasts were severely impaired compared with active wild-type erythroblasts. Furthermore, genes associated with erythroblast maturation and karyopyknosis showed a significantly lower expression in active mutant erythroblasts, recapitulating the maturation defect. Notably, the erythroid differentiation ability and hemoglobin expression of active mutant iPSC-derived hematopoietic progenitor cells (HPCs) were improved by the administration of δ-aminolevulinic acid (ALA), confirming the suitability of the cells for drug testing. The administration of a DNA demethylating agent, azacitidine, reactivated the silent wild-type ALAS2 allele in active mutant iPSC-derived HPCs and ameliorated the erythroid differentiation defects, suggesting that azacitidine is a potential novel therapeutic drug for female XLSA. Our patient-specific iPSC platform provides novel biological and therapeutic insights for XLSA.

2021-12-21 | GSE176008 | GEO

Abcb7, the gene responsible for X-linked sideroblastic anemia with ataxia, is essential for hematopoiesis.

Project description:X-linked sideroblastic anemia with ataxia (XLSA/A) is a rare syndromic form of inherited sideroblastic anemia associated with spinocerebellar ataxia, and is due to mutations in the mitochondrial ATP-binding cassette transporter Abcb7. Here, we show that Abcb7 is essential for hematopoiesis and formally demonstrate that XLSA/A is due to partial loss of function mutations in Abcb7 that directly or indirectly inhibit heme biosynthesis.

| S-EPMC1852240 | biostudies-literature

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