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Query: UMLS:C0004134 (ataxia)
 15,886 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We have identified a compound dinucleotide repeat within intron 7 of the human erythroid 5-aminolevulinate synthase (ALAS2) gene with a minimum of 9 alleles and heterozygosity of 78%. ALAS2 was placed on the multipoint linkage map of the X chromosome in the pericentromeric region with the locus order: pter-(DXS255, TFE3, DXS146)-(DXS14, ALAS2, DXZ1)-AR-(DXS153, DXS159)-qter. No recombination was observed between ALAS2 and the centromere marker DXZ1. As ALAS2 has recently been shown to be the defective locus in X-linked pyridoxine-responsive sideroblastic anemia (PRSA), the ALAS2 marker has allowed placement of the gene for PRSA into the multipoint linkage map of the X chromosome. With the previous exclusion of close linkage between DXS14 and sideroblastic anemia with ataxia, our data show that there are at least two loci for X-linked sideroblastic anemia.
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PMID:Identification of a highly polymorphic marker within intron 7 of the ALAS2 gene and suggestion of at least two loci for X-linked sideroblastic anemia. 130 Nov 72

The erythroid-specific (ALAS2) and housekeeping (ALAS1) genes encoding delta-aminolevulinate synthase have recently been mapped to chromosomes Xp21.1----q21 and 3p21, respectively. The erythroid-specific gene is a candidate for mutations resulting in X-linked sideroblastic anemia. Analysis of DNA from hybrid clones containing translocations in the region Xp11.21----Xq21.3 permitted the finer localization of the ALAS2 gene with respect to other loci and breakpoints within this region. These studies localized the ALAS2 gene to the distal subregion of Xp11.21 in Interval 5 indicating the following gene order: Xpter-OATL2-[L62-3A, Xp11.21; A62-1A-4b, Xp11.21]-(ALAS2, DXS323)-[B13-3, Xp11.21; C9-5, Xp11.21]-(DXS14, DXS429)-DXS422-(DXZ1, Xcen). Thus, the reported linkage of acquired sideroblastic anemia and sideroblastic anemia with ataxia to Xq13 presumably results from genes other than ALAS2.
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PMID:Assignment of human erythroid delta-aminolevulinate synthase (ALAS2) to a distal subregion of band Xp11.21 by PCR analysis of somatic cell hybrids containing X; autosome translocations. 157 84

Molecular linkage analysis was performed on a kindred with X-linked sideroblastic anemia and ataxia. Two-point analysis with a DNA probe for phosphoglycerate kinase (PGK1), which maps to Xq13, suggested linkage to the disorder by a lod score of at least 2.60 at a recombination fraction of zero. The disease in this kindred appears to be clinically and genetically distinct from that in previously reported families with X-linked hereditary ataxia or spastic paraparesis. No mapping data are available for inherited X-linked sideroblastic anemia without neurologic abnormalities. However, structural alterations of band Xq13 may be involved in the development of idiopathic acquired sideroblastic anemia. No alterations in the restriction patterns of two X-linked genes involved in erythrocyte formation-i.e., a DNA-binding protein (GF-1) and 5-aminolevulinate synthase (ALAS)-were detected in DNA from affected males, arguing against a large deletion in either of these candidate genes.
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PMID:X-linked sideroblastic anemia and ataxia: linkage to phosphoglycerate kinase at Xq13. 167 20

Two siblings, a male and a female, had severe axonal neuropathy and sideroblastic anemia. Despite a distinct clinical picture with areflexia, ataxia, hypotonia, optic atrophy, and progressive sensory neural hearing loss, no definite diagnosis could be reached and the older sibling died at 6 years of age of respiratory failure. It is proposed that the two affected siblings have a new form of autosomal-recessive axonal hereditary sensory motor neuropathy.
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PMID:New form of autosomal-recessive axonal hereditary sensory motor neuropathy. 980 45

The sideroblastic anemias are a heterogeneous group of acquired and inherited bone marrow disorders defined by the presence of pathologic iron deposits in erythroblast mitochondria. While the pathogenesis of almost all cases of acquired sideroblastic anemia is unknown, the molecular genetic basis for several of the inherited forms have now been described. Initially, mutations in ALAS2 in X-linked sideroblastic anemia (XLSA) focused attention on the heme biosynthetic pathway as a primary cause of sideroblastic anemia. However, the subsequent description of the genes involved in XLSA with ataxia, thiamine-responsive megaloblastic anemia, and Pearson marrow-pancreas syndrome have implicated other pathways, including mitochondrial oxidative phosphorylation, thiamine metabolism, and iron-sulfur cluster biosynthesis, as primary defects in sideroblastic anemias that may only secondarily impact heme metabolism.
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PMID:The genetics of inherited sideroblastic anemias. 1238 2

Mitochondria are involved in hematopoietic cell homeostasis through multiple ways such as oxidative phosphorylation, various metabolic processes and the release of cytochrome c in the cytosol to trigger caspase activation and cell death. In erythroid cells, the mitochondrial steps in heme synthesis, iron (Fe) metabolism and Fe-sulfur (Fe-S) cluster biogenesis are of particular importance. Mutations in the specific delta-aminolevulinic acid synthase (ALAS) 2 isoform that catalyses the first and rate-limiting step in heme synthesis pathway in the mitochondrial matrix, lead to ineffective erythropoiesis that characterizes X-linked sideroblastic anemia (XLSA), the most common inherited sideroblastic anemia. Mutations in the adenosine triphosphate-binding cassette protein ABCB7, identified in XLSA with ataxia (XLSA-A), disrupt the maturation of cytosolic (Fe-S) clusters, leading to mitochondrial Fe accumulation. In addition, large deletions in mitochondrial DNA, whose integrity depends on a specific DNA polymerase, are the hallmark of Pearson's syndrome, a rare congenital disorder with sideroblastic anemia. In acquired myelodysplastic syndromes at early stage, exacerbation of physiological pathways involving caspases and the mitochondria in erythroid differentiation leads to abnormal activation of a mitochondria-mediated apoptotic cell death pathway. In contrast, oncogenesis-associated changes at the mitochondrial level can alter the apoptotic response of transformed hematopoietic cells to chemotherapeutic agents. Recent findings in mitochondria metabolism and functions open new perspectives in treating hematopoietic cell diseases, for example various compounds currently developed to trigger tumor cell death by directly targeting the mitochondria could prove efficient as either cytotoxic drugs or chemosensitizing agents in treating hematological malignancies.
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PMID:Mitochondria in hematopoiesis and hematological diseases. 1689 88

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.
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PMID:Abcb7, the gene responsible for X-linked sideroblastic anemia with ataxia, is essential for hematopoiesis. 1719 98

Refractory Anemia with Ring Sideroblasts (RARS) is an acquired myelodysplastic syndrome (MDS) characterized by an excess iron accumulation in the mitochondria of erythroblasts. The pathogenesis of RARS and the cause of this unusual pattern of iron deposition remain unknown. We considered that the inherited X-linked sideroblastic anemia with ataxia (XLSA/A) might be informative for the acquired disorder, RARS. XLSA/A is caused by partial inactivating mutations of the ABCB7 ATP-binding cassette transporter gene, which functions to enable transport of iron from the mitochondria to the cytoplasm. Furthermore, ABCB7 gene silencing in HeLa cells causes an accumulation of iron in the mitochondria. We have studied the role of ABCB7 in RARS by DNA sequencing, methylation studies, and gene expression studies in primary CD34(+) cells and in cultured erythroblasts. The DNA sequence of the ABCB7 gene is normal in patients with RARS. We have investigated ABCB7 gene expression levels in the CD34(+) cells of 122 MDS cases, comprising 35 patients with refractory anemia (RA), 33 patients with RARS and 54 patients with RA with excess blasts (RAEB), and in the CD34(+) cells of 16 healthy controls. We found that the expression levels of ABCB7 are significantly lower in the RARS group. RARS is thus characterized by lower levels of ABCB7 gene expression in comparison to other MDS subtypes. Moreover, we find a strong relationship between increasing percentage of bone marrow ring sideroblasts and decreasing ABCB7 gene expression levels. Erythroblast cell cultures confirm the low levels of ABCB7 gene expression levels in RARS. These data provide an important link between inherited and acquired forms of sideroblastic anemia and indicate that ABCB7 is a strong candidate gene for RARS.
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PMID:The role of the iron transporter ABCB7 in refractory anemia with ring sideroblasts. 1839 82

Iron-sulfur (Fe-S) proteins contain prosthetic groups consisting of two or more iron atoms bridged by sulfur ligands, which facilitate multiple functions, including redox activity, enzymatic function, and maintenance of structural integrity. More than 20 proteins are involved in the biosynthesis of iron-sulfur clusters in eukaryotes. Defective Fe-S cluster synthesis not only affects activities of many iron-sulfur enzymes, such as aconitase and succinate dehydrogenase, but also alters the regulation of cellular iron homeostasis, causing both mitochondrial iron overload and cytosolic iron deficiency. In this work, we review human Fe-S cluster biogenesis and human diseases that are caused by defective Fe-S cluster biogenesis. Fe-S cluster biogenesis takes place essentially in every tissue of humans, and products of human disease genes, including frataxin, GLRX5, ISCU, and ABCB7, have important roles in the process. However, the human diseases, Friedreich ataxia, glutaredoxin 5-deficient sideroblastic anemia, ISCU myopathy, and ABCB7 sideroblastic anemia/ataxia syndrome, affect specific tissues, while sparing others. Here we discuss the phenotypes caused by mutations in these different disease genes, and we compare the underlying pathophysiology and discuss the possible explanations for tissue-specific pathology in these diseases caused by defective Fe-S cluster biogenesis.
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PMID:Human iron-sulfur cluster assembly, cellular iron homeostasis, and disease. 2048 66

Addition of the trinucleotide cytosine/cytosine/adenine (CCA) to the 3' end of transfer RNAs (tRNAs) is essential for translation and is catalyzed by the enzyme TRNT1 (tRNA nucleotidyl transferase), which functions in both the cytoplasm and mitochondria. Exome sequencing revealed TRNT1 mutations in two unrelated subjects with different clinical features. The first presented with acute lactic acidosis at 3 weeks of age and developed severe developmental delay, hypotonia, microcephaly, seizures, progressive cortical atrophy, neurosensorial deafness, sideroblastic anemia and renal Fanconi syndrome, dying at 21 months. The second presented at 3.5 years with gait ataxia, dysarthria, gross motor regression, hypotonia, ptosis and ophthalmoplegia and had abnormal signals in brainstem and dentate nucleus. In subject 1, muscle biopsy showed combined oxidative phosphorylation (OXPHOS) defects, but there was no OXPHOS deficiency in fibroblasts from either subject, despite a 10-fold-reduction in TRNT1 protein levels in fibroblasts of the first subject. Furthermore, in normal controls, TRNT1 protein levels are 10-fold lower in muscle than in fibroblasts. High resolution northern blots of subject fibroblast RNA suggested incomplete CCA addition to the non-canonical mitochondrial tRNA(Ser(AGY)), but no obvious qualitative differences in other mitochondrial or cytoplasmic tRNAs. Complete knockdown of TRNT1 in patient fibroblasts rendered mitochondrial tRNA(Ser(AGY)) undetectable, and markedly reduced mitochondrial translation, except polypeptides lacking Ser(AGY) codons. These data suggest that the clinical phenotypes associated with TRNT1 mutations are largely due to impaired mitochondrial translation, resulting from defective CCA addition to mitochondrial tRNA(Ser(AGY)), and that the severity of this biochemical phenotype determines the severity and tissue distribution of clinical features.
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PMID:The 3' addition of CCA to mitochondrial tRNASer(AGY) is specifically impaired in patients with mutations in the tRNA nucleotidyl transferase TRNT1. 2565 5


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