Alternative titles; symbols
HGNC Approved Gene Symbol: GLRX5
SNOMEDCT: 773492007;
Cytogenetic location: 14q32.13 Genomic coordinates (GRCh38): 14:95,535,050-95,544,714 (from NCBI)
| Location | Phenotype |
Phenotype MIM number |
Inheritance |
Phenotype mapping key |
|---|---|---|---|---|
| 14q32.13 | Anemia, sideroblastic, 3, pyridoxine-refractory | 616860 | Autosomal recessive | 3 |
| Spasticity, childhood-onset, with hyperglycinemia | 616859 | Autosomal recessive | 3 |
The GLRX5 gene encodes a mitochondrial protein that plays an essential role in iron-sulfur (Fe-S) cluster biogenesis and is important in the maintenance of intracellular iron homeostasis (Ye et al., 2010). It also plays an essential role in mitochondrial Fe-S cluster transfer to apoproteins, such as lipoate synthetase (summary by Baker et al., 2014 and Liu et al., 2016).
Strausberg et al. (2002) identified the human GLRX5 gene as C14ORF87.
Wingert et al. (2005) determined that the human GLRX5 gene encodes a 157-amino acid protein that is highly conserved among zebrafish, mouse, and human.
Wingert et al. (2005) found high expression of Grx5 in developing blood and in liver and heart of zebrafish. In mice, Grx5 expression at embryonic day 7.5 (E7.5) was ubiquitous, but preferential expression in yolk sac blood islands was evident by E8.5. There was progressive downregulation of Grx5 in maturing primitive red cells between E10.5 and E12.5 and high expression in fetal liver at E12.5.
Ye et al. (2010) found that the human GLRX5 gene was expressed in mitochondria in HeLa cells. In the mouse, Glrx5 was expressed at low levels in several tissues such as liver, kidney, lung, and heart, whereas it was expressed at high levels in bone marrow cells, particularly erythrocytes, and in some parts of the brain, including the hippocampus and cerebellum.
Wingert et al. (2005) mapped the GLRX5 gene to human chromosome 14q32 by homology of synteny between human and zebrafish.
Ye et al. (2010) found that GLRX5 knockdown affected the assembly of Fe-S clusters in mitochondria and in cytosol, resulting in decreased mitochondrial aconitase (ACO2; 100850) activity and decreased cytosolic xanthine oxidase (607633) activity. GLRX5 depletion altered intracellular iron homeostasis, with an increase in nonheme iron, most of which accumulated in the mitochondria. H-ferritin was decreased, suggesting cytosolic iron deficiency. GLRX5 bound to and participated in the formation of Fe-S clusters; GLRX5 depletion blocked Fe-S biosynthesis, which activated the IRE binding activity of IRP1, suppressing expression of ALAS2 (301300) and thus interfering with the heme biosynthetic pathway in erythroid cells. The finding indicated that GLRX5 has an important role in heme synthesis and erythropoiesis.
Liu et al. (2016) found that human GLRX5 directly interacts with the ISCU scaffold (611911) in erythroid cells, indicating that it plays a role in mitochondrial transfer of Fe-S to apoproteins.
Sideroblastic Anemia 3
In a southern Italian man with sideroblastic anemia-3 (SIDBA3; 616860), Camaschella et al. (2007) identified a homozygous splice site mutation in the GLRX5 gene (609588.0001).
In a Chinese man with SIDBA3, Liu et al. (2014) identified compound heterozygous missense mutations in the GLRX5 gene (K101Q; 609588.0002 and L148S; 609588.0003). Direct functional studies of the variants were not performed, but mitochondrial Fe-S biogenesis was impaired in patient peripheral blood cells, as demonstrated by decreased FECH (612386) levels.
In a 14-year-old girl with SIDBA3, Daher et al. (2019) identified compound heterozygous mutations in the GLRX5 gene (C69Y, 609588.0006; M128K, 609588.0007). The mutation segregated with the disorder in the family. Functional studies of the variants were not performed, but studies in patient lymphoblastoid cells showed decreased activity in several Fe-S containing enzymes, including mitochondrial respiratory chain complexes I and IV.
Childhood-Onset Spasticity With Hyperglycinemia
In 2 unrelated girls of Lebanese descent with childhood-onset spasticity with hyperglycinemia (SPAHGC; 616859), Baker et al. (2014) identified a homozygous in-frame deletion in the GLRX5 gene (K51del; 609588.0004). The mutation was found by homozygosity mapping and sequencing of candidate genes involved in iron-sulfur cluster biogenesis. A Chinese patient with a similar phenotype was subsequently found to be compound heterozygous for the K51del mutation and a frameshift mutation (609588.0005). Patient cells showed normal GLRX5 protein levels, but there were reduced to absent levels of lipoate on the E2 subunits of the pyruvate dehydrogenase (PDH) and alpha-ketoglutarate dehydrogenase (alpha-KGDH) complexes compared to controls; lipoate levels normalized after transfection with wildtype GLRX5.
In in vitro cellular transfection and functional expression assays, Liu et al. (2016) found that mutations affecting different parts of the GLRX5 protein resulted in different biochemical cellular phenotypes. Specifically, GLRX5-null and K101Q mutations resulted in significantly decreased PDH and alpha-KGDH activities, whereas the L148S and combined K101Q/L148S mutations did not affect these enzyme complexes. Moreover, cells expressing the K51del mutation had normal aconitase activity and expression of FECH, but decreased PDH and alpha-KGDH complex activities. Coexpression of K51del with the K101Q mutation did not rescue this defect, whereas coexpression with the L148S mutation did complement the defect, suggesting that the L148S mutant is capable of proper lipoate biosynthesis. These cellular findings could explain the phenotypic differences between patients with SIDBA3 and SPAHGC.
Wingert et al. (2005) showed that the hypochromic anemia in 'shiraz' (sir) zebrafish mutants is caused by deficiency of grx5, a gene required in yeast for Fe/S cluster assembly. Wingert et al. (2005) found that grx5 is expressed in erythroid cells of zebrafish and mice. Zebrafish grx5 rescued the assembly of delta-grx5 yeast Fe/S, showing that the biochemical function of grx5 is evolutionarily conserved. In contrast to yeast, vertebrates use iron regulatory protein-1 (IRP1; 100880) to sense intracellular iron and regulate mRNA stability or the translation of iron metabolism genes. Wingert et al. (2005) found that loss of Fe/S cluster assembly in sir animals activated IRP1 and blocked heme biosynthesis catalyzed by aminolevulinate synthase-2 (ALAS2; 301300). Overexpression of ALAS2 RNA without the 5-prime iron response element that binds IRP1 rescued sir embryos, whereas overexpression of ALAS2, including the iron response element, did not. Further, antisense knockdown of IRP1 restored sir embryo hemoglobin synthesis. Wingert et al. (2005) concluded that their findings uncover a connection between heme biosynthesis and Fe/S clusters, indicating that hemoglobin production in the differentiating red cell is regulated through Fe/S cluster assembly.
In a southern Italian man with sideroblastic anemia-3 (SIDBA3; 616860), Camaschella et al. (2007) identified a homozygous 294A-G transition in the third nucleotide of the last codon of GLRX5 exon 1. The mutation does not change the encoded glutamine at position 98, but is predicted to interfere with the correct RNA splicing. Patient cells showed decreased GLRX5 expression compared to controls, consistent with a splicing defect. Further analysis indicated dysregulation of iron-binding proteins.
Ye et al. (2010) found undetectable GLRX5 protein levels in cells derived from the patient reported by Camaschella et al. (2007). Mitochondrial aconitase (ACO2; 100850) activity was undetectable, and cytosolic aconitase (ACO1; 100880) activity was decreased to less than 10% of controls. Mitochondrial complex I activity was also decreased to 20% of normal, consistent with a defect in Fe-S cluster biogenesis. Defects in Fe-S cluster biogenesis negatively impacted ALAS2 activity and heme biosynthesis. FECH (612386) levels were decreased in patient lymphoblast cells, but not in patient fibroblasts, further suggesting that GLRX5 has a specific role in hematopoietic cells. However, patient fibroblasts showed punctate iron deposition in a pattern consistent with mitochondrial iron overload. Transfection of patient cells with wildtype GLRX5 rescued morphologic and growth defects and biochemical abnormalities.
In a Chinese man with sideroblastic anemia-3 (SIDBA3; 606860), Liu et al. (2014) identified compound heterozygous missense mutations in the GLRX5 gene: a c.301A-C transversion, resulting in a lys101-to-gln (K101Q) substitution at a highly conserved residue, and a c.443T-C transition, resulting in a leu148-to-ser (L148S; 609588.0003) substitution at a conserved residue.
In in vitro cellular transfection and functional expression assays, Liu et al. (2016) found that the K101Q mutation likely prevents the binding of Fe-S to the GLRX5 protein, whereas the L148S mutation may interfere with Fe-S transfer from GLRX5 to acceptor proteins. Liu et al. (2016) found that the GLRX5-null and K101Q mutations resulted in a significant decrease in pyruvate dehydrogenase (PDH) and alpha-ketoglutarate dehydrogenase (KGDH) activities, whereas the L148S and combined K101Q/L148S mutations did not affect these enzyme complexes, which explained the lack of additional features in the Chinese patient reported by Liu et al. (2014).
For discussion of the c.443T-C transition in the GLRX5 gene, resulting in a leu148-to-ser (L148S) substitution, that was found in compound heterozygous state in a patient with sideroblastic anemia-3 (SIDBA3; 616860) by Liu et al. (2014), see 609588.0002.
In 2 unrelated girls of Lebanese descent with childhood-onset spasticity with hyperglycinemia (SPAHGC; 616859), Baker et al. (2014) identified a homozygous 3-bp deletion (c.151_153delAAG) in exon 1 of the GLRX5 gene, resulting in the deletion of conserved residue lys51 (K51del), which is in the glutaredoxin domain. The mutation, which was found by homozygosity mapping and sequencing of candidate genes involved in iron-sulfur cluster biogenesis, segregated with the disorder in both families and was not found in 172 Lebanese controls. Patient cells showed normal GLRX5 protein levels, but there were reduced to absent levels of lipoate on the E2 subunits of the pyruvate dehydrogenase (PDH) and alpha-ketoglutarate dehydrogenase (alpha-KGDH) complexes compared to controls; lipoate levels normalized after transfection with wildtype GLRX5. A Chinese patient with a similar phenotype was subsequently found to be compound heterozygous for the K51del mutation and an 8-bp insertion (c.82_83insGCGTGCGG; 609588.0005), resulting in a frameshift and premature termination (Gly28GlyfsTer25). Each unaffected parent was heterozygous for 1 of the mutations, neither of which was found in 188 control Chinese alleles. The findings suggested that GLRX5 likely functions in the pathway that provides an iron-sulfur cluster to lipoate synthase.
In in vitro cellular transfection and functional expression assays, Liu et al. (2016) found that cells expressing the K51del mutation had normal aconitase (ACO2; 100850) activity and expression of FECH (612386), but decreased PDH and alpha-KGDH complex activities: coexpression with the K101Q (609588.0002) mutation did not rescue this defect, whereas coexpression with the L148S (609588.0003) mutation did complement the defect, suggesting that the L148S mutant is capable of proper lipoate biosynthesis.
For discussion of the 8-bp insertion (c.82_83insGCGTGCGG) in exon 1 of the GLRX5 gene, resulting in a frameshift and premature termination (gly28GlyfsTer25), that was found in compound heterozygous state in a patient with childhood-onset spasticity with hyperglycinemia (SPAHGC; 616859) by Baker et al. (2014), see 609588.0004.
In a 14-year-old girl with sideroblastic anemia-3 (SIDBA3; 616860), Daher et al. (2019) identified compound heterozygosity for mutations in the GLRX5 gene: a c.200G-A transition (c.200G-A, NM_016417) in exon 1, resulting in a cys67-to-tyr (C67Y) substitution, inherited from her father, and a c.383T-A transversion in exon 2, resulting in a met128-to-lys (M128K; 609588.0007), inherited from her mother. The C67Y variant is located in a highly conserved region at a position involved in iron cluster coordination; the M128K variant is located in a highly conserved region on the surface of the protein. The mutations were identified by Sanger sequencing. mRNA expression of GLXR5 was not affected in patient lymphoblastoid and CD34+ cells.
For discussion of the c.383T-A transversion (c.383T-A, NM_016417) in the GLRX5 gene, resulting in a met128-to-lys (M128K) substitution, that was found in compound heterozygous state in a patient with sideroblastic anemia-3 (SIDBA3; 616860) by Daher et al. (2019), see (609588.0006).
Baker, P. R., Jr., Friederich, M. W., Swanson, M. A., Shaikh, T., Bhattacharya, K., Scharer, G. H., Aicher, J., Creadon-Swindell, G., Geiger, E., MacLean, K. N., Lee, W. T., Deshpande, C., and 17 others. Variant non ketotic hyperglycinemia is caused by mutations in LIAS, BOLA3 and the novel gene GLRX5. Brain 137: 366-379, 2014. [PubMed: 24334290] [Full Text: https://doi.org/10.1093/brain/awt328]
Camaschella, C., Campanella, A., De Falco, L., Boschetto, L., Merlini, R., Silvestri, L., Levi, S., Iolascon, A. The human counterpart of zebrafish shiraz shows sideroblastic-like microcytic anemia and iron overload. Blood 110: 1353-1358, 2007. [PubMed: 17485548] [Full Text: https://doi.org/10.1182/blood-2007-02-072520]
Daher, R., Mansouri, A., Martelli, A., Bayart, S., Manceau, H., Callebaut, I., Moulouel, B., Gouya, L., Puy, H., Kannengiesser, C., Karim, Z. GLRX5 mutations impair heme biosynthetic enzymes ALA synthase 2 and ferrochelatase in human congenital sideroblastic anemia. Molec. Genet. Metab. 128: 342-351, 2019. [PubMed: 30660387] [Full Text: https://doi.org/10.1016/j.ymgme.2018.12.012]
Liu, G., Guo, S., Anderson, G. J., Camaschella, C., Han, B., Nie, G. Heterozygous missense mutations in the GLRX5 gene cause sideroblastic anemia in a Chinese patient. (Letter) Blood 124: 2750-2751, 2014. [PubMed: 25342667] [Full Text: https://doi.org/10.1182/blood-2014-08-598508]
Liu, G., Wang, Y., Anderson, G. J., Camaschella, C., Chang, Y., Nie, G. Functional analysis of GLRX5 mutants reveals distinct functionalities of GLRX5 protein. J. Cell. Biochem. 117: 207-217, 2016. [PubMed: 26100117] [Full Text: https://doi.org/10.1002/jcb.25267]
Strausberg, R. L., Feingold, E. A., Grouse, L. H., Derge, J. G., Klausner, R. D., Collins, F. S., Wagner, L., Shenmen, C. M., Schuler, G. D., Altschul, S. F., Zeeberg, B., Buetow, K. H., and 71 others. Generation and initial analysis of more than 15,000 full-length human and mouse cDNA sequences. Proc. Nat. Acad. Sci. 99: 16899-16903, 2002. [PubMed: 12477932] [Full Text: https://doi.org/10.1073/pnas.242603899]
Wingert, R. A., Galloway, J. L., Barut, B., Foott, H., Fraenkel, P., Axe, J. L., Weber, G. J., Dooley, K., Davidson, A. J., Schmidt, B., Paw, B. H., Shaw, G. C., Kingsley, P., Palis, J., Schubert, H., Chen, O., Kaplan, J., Tubingen 2000 Screen Consortium, Zon, L. I. Deficiency of glutaredoxin 5 reveals Fe-S clusters are required for vertebrate haem synthesis. (Letter) Nature 436: 1035-1039, 2005. Note: Erratum: Nature 437: 920 only, 2005. [PubMed: 16110529] [Full Text: https://doi.org/10.1038/nature03887]
Ye, H., Jeong, Y., Ghosh, M. C., Kovtunovych, G., Silvestri, L., Ortillo, D., Uchida, N., Tisdale, J., Camaschella, C., Rouault, T. A. Glutaredoxin 5 deficiency causes sideroblastic anemia by specifically impairing heme biosynthesis and depleting cytosolic iron in human erythroblasts. J. Clin. Invest. 120: 1749-1761, 2010. [PubMed: 20364084] [Full Text: https://doi.org/10.1172/JCI40372]