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Luo J, Guo H, Feng L, Yang L, Chen X, Du T, Hu M, Yao H, Chen X. Case report: Novel compound-heterozygous mutations in the TCN2 gene identified in a chinese girl with transcobalamin deficiency. Front Genet 2022; 13:951007. [PMID: 36035190 PMCID: PMC9411981 DOI: 10.3389/fgene.2022.951007] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2022] [Accepted: 07/12/2022] [Indexed: 11/22/2022] Open
Abstract
Transcobalamin (TC) deficiency is a rare autosomal recessive disease characterized by megaloblastic anemia. It is caused by cellular vitamin B12 depletion, which subsequently results in elevated levels of homocysteine and methylmalonic acid. This disease is usually diagnosed by genetic analysis of the TCN2 gene. Here, we described a 2.2-month-old Chinese girl with TC deficiency presenting with diarrhea, fever and poor feeding. Whole-exome sequencing detected a pair of compound-heterozygous mutations in TCN2 gene, c.754-12C>G and c.1031_1032delGA (p.R344Tfs*20). To our knowledge, it is the first time that they were identified and reported in TC deficiency. This study contributes to a better understanding of the TC deficiency, expanding the spectrum of TCN2 mutations in this disorder and also supporting the early diagnosis and proper treatment of similar cases in the future.
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Affiliation(s)
- Juan Luo
- Department of Endocrinology and Metabolism, Wuhan Children’s Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China
| | - Hongxi Guo
- Department of General Surgery, Wuhan Children’s Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China
| | - Lifang Feng
- Department of Endocrinology and Metabolism, Wuhan Children’s Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China
| | - Luhong Yang
- Department of Endocrinology and Metabolism, Wuhan Children’s Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China
| | - Xiaoqian Chen
- Department of Endocrinology and Metabolism, Wuhan Children’s Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China
| | - Tingting Du
- Department of Endocrinology and Metabolism, Wuhan Children’s Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China
| | - Man Hu
- Department of Endocrinology and Metabolism, Wuhan Children’s Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China
| | - Hui Yao
- Department of Endocrinology and Metabolism, Wuhan Children’s Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China
- *Correspondence: Hui Yao, ; Xiaohong Chen,
| | - Xiaohong Chen
- Department of Endocrinology and Metabolism, Wuhan Children’s Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China
- *Correspondence: Hui Yao, ; Xiaohong Chen,
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Guéant JL, Guéant-Rodriguez RM, Alpers DH. Vitamin B12 absorption and malabsorption. VITAMINS AND HORMONES 2022; 119:241-274. [PMID: 35337622 DOI: 10.1016/bs.vh.2022.01.016] [Citation(s) in RCA: 35] [Impact Index Per Article: 17.5] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
Abstract
Vitamin B12 is assimilated and transported by complex mechanisms that involve three transport proteins, intrinsic factor (IF), haptocorrin (HC) and transcobalamin (TC) and their respective membrane receptors. Vitamin deficiency is mainly due to inadequate dietary intake in vegans, and B12 malabsorption is related to digestive diseases. This review explores the physiology of vitamin B12 absorption and the mechanisms and diseases that produce malabsorption. In the stomach, B12 is released from food carrier proteins and binds to HC. The degradation of HC by pancreatic proteases and the pH change trigger the transfer of B12 to IF in the duodenum. Cubilin and amnionless are the two components of the receptor that mediates the uptake of B12 in the distal ileum. Part of liver B12 is excreted in bile, and undergoes an enterohepatic circulation. The main causes of B12 malabsorption include inherited disorders (Intrinsic factor deficiency, Imerslund-Gräsbeck disease, Addison's pernicious anemia, obesity, bariatric surgery and gastrectomies. Other causes include pancreatic insufficiency, obstructive Jaundice, tropical sprue and celiac disease, bacterial overgrowth, parasitic infestations, Zollinger-Ellison syndrome, inflammatory bowel diseases, chronic radiation enteritis of the distal ileum and short bowel. The assessment of B12 deficit is recommended in the follow-up of subjects with bariatric surgery. The genetic causes of B12 malabsorption are probably underestimated in adult cases with B12 deficit. Despite its high prevalence in the general population and in the elderly, B12 malabsorption cannot be anymore assessed by the Schilling test, pointing out the urgent need for an equivalent reliable test.
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Affiliation(s)
- Jean-Louis Guéant
- University of Lorraine, INSERM UMR_S 1256, Nutrition, Genetics, and Environmental Risk Exposure (NGERE), Faculty of Medicine of Nancy, Nancy, France; Department of Biochemistry, Molecular Biology, Nutrition, and Metabolism, University Hospital of Nancy, Nancy, France; Department of Hepato-Gastroenterology, University Hospital of Nancy, Nancy, France.
| | - Rosa-Maria Guéant-Rodriguez
- University of Lorraine, INSERM UMR_S 1256, Nutrition, Genetics, and Environmental Risk Exposure (NGERE), Faculty of Medicine of Nancy, Nancy, France; Department of Biochemistry, Molecular Biology, Nutrition, and Metabolism, University Hospital of Nancy, Nancy, France
| | - David H Alpers
- Department of Internal Medicine, Division of Gastroenterology, Washington University School of Medicine, St Louis, MO, United States.
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Rigaudière F, Nasser H, Delouvrier E, Milani P, Schiff M. Subclinical maculopathy and retinopathy in transcobalamin deficiency: a 10-year follow-up. Doc Ophthalmol 2021; 144:53-65. [PMID: 34491492 DOI: 10.1007/s10633-021-09849-5] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2021] [Accepted: 08/24/2021] [Indexed: 10/20/2022]
Abstract
INTRODUCTION Transcobalamin (TC) transports cobalamin (vitamin B12) from plasma into cells. Its congenital deficiency is a rare autosomal recessive disorder due to mutations in the TCN2 gene. It causes intracellular cobalamin depletion with early onset in the first months of life, failure to thrive with pallor due to megaloblastic anemia. It can be associated with pancytopenia, gastrointestinal symptoms with vomiting, diarrhea, and neurological complications with myelopathy. Aggressive vitamin B12 parenteral therapy must be instituted early and continuously. Retinopathy and maculopathy are rarely associated with this condition. SUBJECT We report the electrophysiological results of one TC-deficient patient diagnosed at the age of 4 months immediately and continuosly treated by hydroxocobalamin IM. Her visual function was followed by eight ophthalmological assessments, eight flash-ERG, six EOG, one mf-ERG, and seven P-ERG recordings over a 10-year period, between the age of 2y 9 m and 12y 6 m. RESULTS Her ophthalmological assessment including visual acuity, fundi, optical coherent tomography (OCT), and retinal nerve fiber layer (RNFL) remained normal. From the age of 2y 9 m to 5y, dark-adapted and light-adapted flash-ERGs, EOGs and pattern-ERG were normal. From the age of 6y 4 m to 12y 6 m, dark-adapted flash-ERGs and EOGs remained normal. Cone a-wave amplitudes remained normal, whereas cone b-wave and flicker-response amplitudes were decreased. At the age of 12y 6 m, mf-ERG N1P1 amplitudes on the central 30° were decreased. From the age of 7y 4 m to 12y 6 m, P-ERG P50 amplitudes were decreased with no N95. COMMENTS While clinical and anatomical assessments remained normal over a 10-year period, patient's electrophysiological results suggested the progressive onset of a subclinical retinopathy of inner-cone dystrophy type, and a subclinical maculopathy on the central 30° including the ganglion cell layer deficiency on the central 15°, despite continuous intramuscular treatment, RPE and scotopic system remaining normal. The origins of such subclinical retinopathy and maculopathy are unknown and independent of early disease identification and aggressive intramuscular hydroxocobalamin therapy.
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Affiliation(s)
- Florence Rigaudière
- Service de Physiologie Clinique. Explorations Fonctionnelles, DMU DREAM, Hôpital Lariboisière, AP-HP, Paris, France. .,Faculté de Médecine Paris-Diderot, Université de Paris, Paris, France.
| | - Hala Nasser
- Département de Génétique, Hôpital Robert Debré, AP-HP, Paris, France.,Explorations Fonctionnelles, Hôpital Robert Debré, AP-HP, Paris, France
| | | | - Paolo Milani
- Service de Physiologie Clinique. Explorations Fonctionnelles, DMU DREAM, Hôpital Lariboisière, AP-HP, Paris, France
| | - Manuel Schiff
- Reference Center for Inborn Errors of Metabolism, Robert Debré Hospital, AP-HP, Paris, France.,Reference Center for Inborn Errors of Metabolism, Faculté de Médecine Paris-Descartes, Necker University Hospital, AP-HP, Université de Paris, Paris, France.,Institut Imagine, Inserm UMRS_1163, Paris, France
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Ünal S, Karahan F, Arıkoğlu T, Akar A, Kuyucu S. Different Presentations of Patients with Transcobalamin II Deficiency: A Single-Center Experience from Turkey. Turk J Haematol 2018; 36:37-42. [PMID: 30185401 PMCID: PMC6373502 DOI: 10.4274/tjh.galenos.2018.2018.0230] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022] Open
Abstract
Objective: Transcobalamin II deficiency is a rare autosomal recessive disease characterized by decreased cobalamin availability, which in turn causes accumulation of homocysteine and methylmalonic acid. The presenting clinical features are failure to thrive, diarrhea, megaloblastic anemia, pancytopenia, neurologic abnormalities, and also recurrent infections due to immune abnormalities in early infancy. Materials and Methods: Here, we report the clinical and laboratory features of six children with transcobalamin II deficiency who were all molecularly confirmed. Results: The patients were admitted between 1 and 7 months of age with anemia or pancytopenia. Unexpectedly, one patient had a serum vitamin B12 level lower than the normal range and another one had nonsignificantly elevated serum homocysteine levels. Four patients had lymphopenia, four had neutropenia and three also had hypogammaglobulinemia. Suggesting the consideration of transcobalamin II deficiency in the differential diagnosis of immune deficiency. Hemophagocytic lymphohistiocytosis was also detected in one patient. Furthermore, two patients had vacuolization in the myeloid lineage in bone marrow aspiration, which may be an additional finding of transcobalamin II deficiency. The hematological abnormalities in all patients resolved after parenteral cobalamin treatment. In follow-up, two patients showed neurological impairments such as impaired speech and walking. Among our six patients who were all molecularly confirmed, two had the mutation that was reported in transcobalamin II-deficient patients of Turkish ancestry. Also, a novel TCN2 gene mutation was detected in one of the remaining patients. Conclusion: Transcobalamin II deficiency should be considered in the differential diagnosis of infants with immunological abnormalities as well as cytopenia and neurological dysfunction. Early recognition of this rare condition and initiation of adequate treatment is critical for control of the disease and better prognosis.
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Affiliation(s)
- Selma Ünal
- Mersin University Faculty of Medicine, Department of Pediatric Hematology, Mersin, Turkey
| | - Feryal Karahan
- Mersin University Faculty of Medicine, Department of Pediatric Hematology, Mersin, Turkey
| | - Tuğba Arıkoğlu
- Mersin University Faculty of Medicine, Department of Pediatric Allergy and Immunology, Mersin, Turkey
| | - Asuman Akar
- Mersin University Faculty of Medicine, Department of Pediatric Infectious Diseases, Mersin, Turkey
| | - Semanur Kuyucu
- Mersin University Faculty of Medicine, Department of Pediatric Allergy and Immunology, Mersin, Turkey
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Dhillon VS, Zabaras D, Almond T, Cavuoto P, James-Martin G, Fenech M. Whey protein isolate improves vitamin B12and folate status in elderly Australians with subclinical deficiency of vitamin B12. Mol Nutr Food Res 2017; 61. [DOI: 10.1002/mnfr.201600915] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2016] [Revised: 12/05/2016] [Accepted: 12/12/2016] [Indexed: 12/26/2022]
Affiliation(s)
- Varinderpal S. Dhillon
- Genome Health Commonwealth Scientific and Industrial Research Organisation Health and Biosecurity; Adelaide South Australia Australia
| | - Dimitrios Zabaras
- Genome Health Commonwealth Scientific and Industrial Research Organisation Health and Biosecurity; Adelaide South Australia Australia
| | - Theodora Almond
- Genome Health Commonwealth Scientific and Industrial Research Organisation Health and Biosecurity; Adelaide South Australia Australia
| | - Paul Cavuoto
- Genome Health Commonwealth Scientific and Industrial Research Organisation Health and Biosecurity; Adelaide South Australia Australia
| | - Genevieve James-Martin
- Genome Health Commonwealth Scientific and Industrial Research Organisation Health and Biosecurity; Adelaide South Australia Australia
| | - Michael Fenech
- Genome Health Commonwealth Scientific and Industrial Research Organisation Health and Biosecurity; Adelaide South Australia Australia
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Abstract
ABSTRACT:The following review indicates that the impact of cobalamin on neurologic disease extends far beyond the traditional myelopathy of classical pernicious anemia. The delineation of a broad spectrum of inherited disorders of cobalamin processing has served to illustrate and precisely define each step in the normal absorption, transport and intracellular metabolism of this essential vitamin. Recent clinical work has extended the boundaries of acquired cobalamin deficiency to encompass a variety of neuropsychiatric disturbances without identifiable concomitant hematologic derangements and emphasized the utility and sensitivity of new laboratory tests. These findings will demand increased vigilance from clinicians so that atypical and subtle cobalamin deficiency states will be readily diagnosed. The wide range of neurologic dysfunction observed in both inherited and acquired disorders of cobalamin metabolism challenges basic scientists to delineate cobalamin’s presumed important role in the normal development and homeostasis of the nervous system.
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Parvaneh N, Quartier P, Rostami P, Casanova JL, de Lonlay P. Inborn errors of metabolism underlying primary immunodeficiencies. J Clin Immunol 2014; 34:753-71. [PMID: 25081841 DOI: 10.1007/s10875-014-0076-6] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2014] [Accepted: 07/02/2014] [Indexed: 01/19/2023]
Abstract
A number of inborn errors of metabolism (IEM) have been shown to result in predominantly immunologic phenotypes, manifesting in part as inborn errors of immunity. These phenotypes are mostly caused by defects that affect the (i) quality or quantity of essential structural building blocks (e.g., nucleic acids, and amino acids), (ii) cellular energy economy (e.g., glucose metabolism), (iii) post-translational protein modification (e.g., glycosylation) or (iv) mitochondrial function. Presenting as multisystemic defects, they also affect innate or adaptive immunity, or both, and display various types of immune dysregulation. Specific and potentially curative therapies are available for some of these diseases, whereas targeted treatments capable of inducing clinical remission are available for others. We will herein review the pathogenesis, diagnosis, and treatment of primary immunodeficiencies (PIDs) due to underlying metabolic disorders.
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Affiliation(s)
- Nima Parvaneh
- Research Center for Immunodeficiencies, Tehran University of Medical Sciences, Tehran, Iran,
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Prasad C, Rosenblatt DS, Corley K, Cairney AEL, Rupar CA. Transcobalamin (TC) deficiency--potential cause of bone marrow failure in childhood. J Inherit Metab Dis 2008; 31 Suppl 2:S287-92. [PMID: 18956254 DOI: 10.1007/s10545-008-0864-3] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/04/2008] [Revised: 08/21/2008] [Accepted: 09/22/2008] [Indexed: 11/27/2022]
Abstract
It is unusual for inborn errors of metabolism to be considered in the investigative work-up of pancytopenia. We report a family in which the proband presented with failure to thrive at 2 months of age and subsequent bone marrow failure. A previous sibling had died at 7 months of age with suspected leukaemia. Haematological findings in the proband were significant for pancytopenia, and bone marrow aspiration showed dysplastic changes in all cell lineages. Urinary organic acid analysis revealed elevated methylmalonic acid. The synthesis of transcobalamin II (transcobalamin, TC) by cultured fibroblasts was markedly reduced, confirming the diagnosis of TC deficiency. The proband and his younger asymptomatic sister (also found to have TC deficiency) were homozygous for R399X (c.1195C>T), a novel mutation resulting in the loss of the C- terminal 29 amino acids of TC, a highly conserved region. Response to parenteral vitamin B(12) in the proband was dramatic. At 6 years 3 months of age, physical examination is normal and developmental level is age appropriate. His sister is clinically asymptomatic and is also developing normally. Propionylcarnitine concentrations were not elevated in the newborn screening cards from the proband and sister, but that was for specimens retrieved from storage after 7 years and 5 years, respectively. Inherited and acquired cobalamin disorders should both be considered in the differential diagnosis of bone marrow failure syndromes in young children. Early detection of the metabolic causes of bone marrow failure can ensure prompt recovery in some cases involving the vitamin B(12) pathway.
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Affiliation(s)
- C Prasad
- Department of Pediatrics, Children's Hospital of Western Ontario and University of Western Ontario, London, Ontario, Canada.
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Thauvin-Robinet C, Roze E. Troubles du métabolisme des cobalamines chez l’adulte. Rev Neurol (Paris) 2007; 163:911-8. [DOI: 10.1016/s0035-3787(07)92634-x] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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Obeid R, Kuhlmann M, Kirsch CM, Herrmann W. Cellular uptake of vitamin B12 in patients with chronic renal failure. Nephron Clin Pract 2004; 99:c42-8. [PMID: 15637428 DOI: 10.1159/000083132] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2004] [Accepted: 08/03/2004] [Indexed: 01/25/2023] Open
Abstract
BACKGROUND/AIMS Elevated concentration of plasma homocysteine (tHcy) is common in renal patients, however, the reason behind the resistance to vitamin B(12) and folate therapy are poorly understood. METHODS We investigated vitamin B12 uptake by mononuclear cells (MC) from predialysis patients (n = 19) as compared to healthy controls (n = 15). Serum levels of tHcy, methylmalonic acid and cystathionine, holotranscobalamin (holoTC), total vitamin B12 and folate were also measured. RESULTS The uptake of vitamin B12 by MC from renal patients was lower than that by MC from controls (9.3 vs. 12.5 pg/3 x 10(6) cells; p = 0.001). Nonetheless, the receptor-binding capacity was comparable between patients and controls (6.1 vs. 6.5 pg/3 x 10(6) cells; p = 0.627). Average reduction of vitamin B12 uptake in patients as compared to the controls was 18.1%. CONCLUSIONS Our results show that vitamin B12 uptake is impaired in MC from renal patients, with no evidence that the surface receptor is down-regulated. High serum concentrations of holoTC are common in renal patients and might be related to a generalized resistance to this vitamin. Serum concentrations of vitamin B12 within the reference range are not likely to ensure vitamin delivery into the cells. Supraphysiological doses of vitamin B12 may be necessary to deliver a sufficient amount of the vitamins to the cells via mechanisms largely independent of holoTC receptor.
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Affiliation(s)
- Rima Obeid
- Department of Clinical Chemistry, Central Laboratory, Saarland University Hospital, Homburg, Germany
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Kalra S, Seetharam S, Yammani RR, Seetharam B. Rat transcobalamin: cloning and regulation of mRNA expression. J Physiol 2004; 556:623-35. [PMID: 14724191 PMCID: PMC1664936 DOI: 10.1113/jphysiol.2003.058727] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Transcobalamin (TC) has been cloned and used for studying its gene expression in the rat. TC mRNA is distributed widely in adult rat tissues, but at different levels (kidney > liver > lung > yolk sac > intestine > heart > brain > spleen > muscle). TC mRNA levels were 4-fold higher in the jejunum and ileum compared to its levels in the duodenum. During postnatal development, TC mRNA levels in the ileum declined 4-fold from day 4 to day 12, but increased by 5-fold between days 12 and 24. In contrast, TC mRNA levels increased by 2.5-fold in the kidney from day 4 to day 12 and then declined by 2-fold by day 24. Adrenalectomy of adult rats resulted in a 4-fold decline in ileal levels of TC mRNA and a 50% decline in the ileal mucosal formation of the TC-[(57)Co] cobalamin (Cbl) complex following oral administration of [(57)Co]Cbl complexed to gastric intrinsic factor (IF). Cortisone treatment reversed these changes noted in the ileum. In contrast to ileum, kidney TC mRNA levels were not altered significantly in adrenalectomized rats before and after cortisone treatment. Taken together, this study has provided evidence for the regulation of TC gene expression in the rat kidney and intestine during their postnatal development, and cortisone selectively regulates ileal but not kidney TC mRNA levels.
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Affiliation(s)
- Seema Kalra
- VA Medical Center, Research 151, 5000 West National Avenue, Milwaukee, WI 53295, USA
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de Lonlay P, Fenneteau O, Touati G, Mignot C, Billette de Villemeur T, Rabier D, Blanche S, Ogier de Baulny H, Saudubray JM. [Hematologic manifestations of inborn errors of metabolism]. Arch Pediatr 2002; 9:822-35. [PMID: 12205794 DOI: 10.1016/s0929-693x(02)00005-2] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
Haematological symptoms can be helpful for the diagnosis of metabolic diseases. A megaloblastic anemia orientates to folate and cobalamine anomalies when associated with homocystinemia and decreased plasma methionine levels, or to congenital oroticuria (hypochromia), Pearson syndrome (sideroblasts and vacuolisation of precursors) and thiamine transporter abnormality (sideroblasts) in the absence of homocystinuria. An hemolytic anemia orientates to anomalies of anaerobic glycolysis, heme synthesis, or iron metabolism, and Wilson disease. A pancytopenia orientates to organic aciduria, lysinuric protein intolerance, mevalonic aciduria and lysosomal storage diseases (Gaucher, Niemann Pick, Wolman) when hepatosplenomegaly is present. Uremic hemolytic syndrome and hemophagocytic lymphohistiocytosis respectively orientate to B12 anomalies, lysinuric protein intolerance, lysosomal storage diseases and organic aciduria.
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Affiliation(s)
- P de Lonlay
- Département de pédiatrie, hôpital Necker-Enfants Malades, 149, rue de Sèvres, 75743 Pariscedex 15, France.
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Abstract
Transcobalamin II (TC II), a nonglycoprotein secretory protein of molecular mass 43 kDa, and its plasma membrane receptor (TC II-R), a heavily glycosylated protein with a monomeric molecular mass of 62 kDa, are essential components of plasma cobalamin (Cbl; vitamin B12) transport to all cells. Evidence from studies over the past 10 years has provided some important information on their structure, regulation of expression, and function. Some of the specific findings include (a) identification of the structural relationship of the ligand TC II with other members of the Cbl-binding family of proteins, intrinsic factor (IF) and haptocorrin (HC), (b) regulation of TC II gene expression, (c) molecular basis for human TC II deficiency in patients with a lack of plasma TC II, (d) membrane expression, interactions, and dimerization of TC II-R, and (e) targeting and function of TC II-R in polarized epithelial cells. It is hoped that some of the recent findings presented in this review will provide new insights into the structure and function of these two fascinating proteins and stimulate future research in this area.
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Affiliation(s)
- B Seetharam
- Department of Medicine, Medical College of Wisconsin, Milwaukee, USA
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Bibi H, Gelman-Kohan Z, Baumgartner ER, Rosenblatt DS. Transcobalamin II deficiency with methylmalonic aciduria in three sisters. J Inherit Metab Dis 1999; 22:765-72. [PMID: 10518276 DOI: 10.1023/a:1005507204491] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Transcobalamin II (TC II) is a plasma protein that binds vitamin B12 (cobalamin, Cbl) and facilitates cellular Cbl uptake by receptor-mediated endocytosis. In autosomal recessive TC II deficiency, intracellular Cbl deficiency results in an early onset of megaloblastic anaemia that may be accompanied by neurological abnormalities. Inadequate treatment may lead to neurological abnormalities. We describe three sisters, the daughters of first cousins of Moroccan origin, with TC II deficiency requiring continuous and long-term vitamin B12 treatment. The diagnosis was suspected from the finding of low unsaturated vitamin B12 binding capacity and confirmed by absence of detectable TC II by radioimmunoassay and by inability of cultured fibroblasts to synthesize TC II.
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Affiliation(s)
- H Bibi
- Pediatric Department, Clinical Genetic Institute Barzilai Medical Center, Ashkelon, Israel
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Abstract
Dietary cobalamin (Cbl) (vitamin B12) is utilized as methyl-Cbl and the coenzyme 5'-deoxyadenosyl Cbl by cells of the body that have the enzymes methionine synthase and methyl malonyl CoA mutase, which convert homocysteine to methionine and methyl malonyl CoA to succinyl CoA, respectively. Prior to conversions and utilizations as the active alkyl forms of Cbl, dietary Cbl is absorbed and transported across cellular plasma membranes by two receptor-mediated events. First, dietary and biliary Cbl bound to gastric intrinsic factor (IF) presented apically to the ileal absorptive enterocytes is transported to the circulation by receptor-mediated endocytosis via apically expressed IF-Cbl receptor. Second, Cbl bound to plasma transcobalamin (TC) II is taken up from the circulation by all cells via a TC II receptor expressed in the plasma membrane of these cells, and in polarized cells via a TC II receptor expressed in the basolateral membranes. This review updates recent work and focuses on (a) the molecular and cellular aspects of Cbl binding protein ligands, IF and TC II, and their cell-surface receptors, IF-Cbl receptor and TC II receptor; (b) the cellular sorting pathways of internalized Cbl bound to IF and TC II in polarized epithelial cells; and (c) the absorption and transport disorders that cause Cbl deficiency.
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Affiliation(s)
- B Seetharam
- Department of Medicine and Biochemistry, Medical College of Wisconsin, Milwaukee, USA.
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Bose S, Seetharam S, Dahms NM, Seetharam B. Bipolar functional expression of transcobalamin II receptor in human intestinal epithelial Caco-2 cells. J Biol Chem 1997; 272:3538-43. [PMID: 9013602 DOI: 10.1074/jbc.272.6.3538] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
Transcobalamin II (TC II) receptor is expressed in the apical and basolateral membranes of human intestinal mucosa and in post-confluent human intestinal epithelial Caco-2 cells with a 6-7-fold enrichment in basolateral membranes. Caco-2 cells grown on culture inserts bound (at 5 degrees C) 30 and 180 fmol of the ligand, TC II-[57Co]cobalamin (Cbl), to the apical and the basolateral surfaces, respectively. Within 5 h at 37 degrees C, all apically bound Cbl was internalized and subsequently transcytosed as TC II-Cbl. In contrast, all basolateral surface-bound Cbl was internalized and retained by the cells, but transferred from TC II to other cellular proteins. Chloroquine or leupeptin had no effect on the apical to basolateral transcytosis of either [57Co]Cbl or 125I-TC II. In contrast, following basolateral internalization of the ligand, both chloroquine and leupeptin inhibited the intracellular degradation of 125I-TC II, which resulted in secretion of 60-65% of TC II-Cbl complex into the basolateral medium. When 125I-TC II-Cbl was orally administered to rats, intact labeled TC II was detected in the portal blood 4 and 8 h later. These studies suggest that TC II-Cbl is processed when presented to the (a) apical/luminal side by a hitherto unrecognized non-lysosomal pathway in which both TC II and Cbl are transcytosed and (b) basolateral side by the lysosomal pathway in which TC II is degraded and the released Cbl is utilized.
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Affiliation(s)
- S Bose
- Department of Biochemistry, Medical College of Wisconsin and Veterans Administration Medical Center, Milwaukee, Wisconsin 53226, USA
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Linnell JC, Bhatt HR. Inherited errors of cobalamin metabolism and their management. BAILLIERE'S CLINICAL HAEMATOLOGY 1995; 8:567-601. [PMID: 8534962 DOI: 10.1016/s0950-3536(05)80221-5] [Citation(s) in RCA: 27] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Cobalamins are essential biological compounds structurally related to haemoglobin and the cytochromes. Although the basic cobalamin molecule is only synthesized by micro-organisms, all mammalian cells can convert this into the coenzymes adenosylcobalamin (AdoCbl) and methylcobalamin (MeCbl). AdoCbl is the major form in cellular tissues, where it is retained in the mitochondria. MeCbl predominates in blood plasma and certain other body fluids such as breast milk; in cells MeCbl is found in the cytosol. Inherited disorders of cobalamin metabolism are single gene defects, transmitted as recessive traits. They affect absorption, transport or intracellular metabolism of cobalamin. At least 12 different mutations are known, including defects or deficiencies of IF, IF-receptor and TCII, MM-CoA mutase and of the various reductases and synthases required for synthesis of AdoCbl and MeCbl. These have been designated cblA to cblG. Abnormalities are detectable by urine and plasma assays of methylmalonic acid and homocysteine, and plasma and erythrocyte analysis of cobalamin coenzymes, which can reveal deficiencies of MeCbl or AdoCbl. Fibroblast studies discriminate between closely similar defects. In man, AdoCbl is required in only two reactions: the catabolic isomerization of MM-CoA to succinyl-CoA and interconversion of alpha- and beta-leucine. MeCbl is required in the anabolic transmethylation of homocysteine to methionine. Intestinal absorption of cobalamin requires the glycoproteins TCI and IF from the stomach and IF-cobalamin receptors in the ileum. Cobalamin is transported to cells bound to a polypeptide, TCII, is captured by surface receptors and absorbed by endocytosis. The complex is then split in the lysosomes, cobalamin is released and the coenzymes are synthesized. In plasma, 80-90% of the cobalamin is bound to TCI, whose function is uncertain. Megaloblastic anaemia at birth or in the first few weeks of life is a rare but serious event. Myelopathy and developmental delay, with or without seizures may also occur without anaemia. If urine and light-protected blood samples are collected and sent to an appropriate metabolic unit, an inborn error of cobalamin metabolism, including TCII deficiency in which the serum B12 may be normal, can quickly be diagnosed. IF deficiency or Imerslund-Gräsbeck disease usually presents with signs of cobalamin deficiency within the first year of life and can be diagnosed by absorption studies. Current treatment involves dietary protein restriction and/or parenteral OHCbl and the prognosis is very variable. Since lack of MeCbl leads to depressed DNA synthesis affecting rapidly dividing cells in the brain and elsewhere, treatment with this coenzyme should be considered at the earliest stage in appropriate cases.(ABSTRACT TRUNCATED AT 400 WORDS)
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Affiliation(s)
- J C Linnell
- Vitamin B12 Unit, Chelsea and Westminster Hospital, London, UK
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Li N, Seetharam S, Rosenblatt DS, Seetharam B. Expression of transcobalamin II mRNA in human tissues and cultured fibroblasts from normal and transcobalamin II-deficient patients. Biochem J 1994; 301 ( Pt 2):585-90. [PMID: 7913804 PMCID: PMC1137121 DOI: 10.1042/bj3010585] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Transcobalamin II (TCII) is an important plasma transporter of cobalamin (Cbl; vitamin B12). In the present study, TCII gene expression in human and rat tissues and in the fibroblasts of patients with TCII deficiency was investigated. Northern-blot analyses revealed expression of TCII mRNA in many human and rat tissues. In humans, this was 14-fold higher in the kidney than in liver, whereas in the rat the levels of expression were similar in the kidney and liver. Southern-blot analysis of genomic DNA from several species revealed sequence similarity in TCII across species. Metabolic labelling and ribonuclease protection assay revealed a 43 kDa TCII protein and a fully protected TCII mRNA band in normal fibroblasts but not in fibroblasts from three TCII-deficient patients. Southern-blot analysis of genomic DNA from all these fibroblasts revealed identical restriction patterns on BamHI, HindIII, KpnI, MspI and EcoRI digestion. On the basis of these results, we suggest that TCII is expressed in multiple tissues, and its level of expression in tissues varies within the same and across species. Furthermore, the TCII deficiency characterized in this study is due to the absence of TCII protein which in turn is due to the absence or extremely low levels of its mRNA and not to detectable gross alterations in the gene structure.
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Affiliation(s)
- N Li
- Department of Biochemistry, Medical College of Wisconsin, Milwaukee 53226
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Allen RH, Stabler SP, Savage DG, Lindenbaum J. Elevation of 2-methylcitric acid I and II levels in serum, urine, and cerebrospinal fluid of patients with cobalamin deficiency. Metabolism 1993; 42:978-88. [PMID: 8345822 DOI: 10.1016/0026-0495(93)90010-l] [Citation(s) in RCA: 100] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Citrate synthase catalyzes the condensation of acetyl-coenzyme A (CoA) and oxaloacetic acid to form citric acid. The enzyme also catalyzes the condensation of propionyl-CoA and oxaloacetic acid with a maximal reaction velocity (Vmax) approximately 10(-4) times that of acetyl-CoA to form 2-methylcitric acid, which contains two asymmetric carbon atoms and exists as two pairs of related enantiomers designated as 2-methylcitric acid I and II. Cobalamin (Cbl) deficiency can lead to increases in intracellular levels of propionyl-CoA. To assess the magnitude of increased synthesis of 2-methylcitric acid in Cbl deficiency, we developed a new capillary gas chromatographic-mass spectrometric assay and measured 2-methylcitric acid levels in serum and cerebrospinal fluid (CSF) of normal subjects and patients with clinically confirmed Cbl deficiency. The normal range for 2-methylcitric acid level was 60 to 228 nmol/L for serum in 50 normal blood donors and 323 to 1,070 nmol/L for CSF in 19 normal subjects. In 50 patients with clinically confirmed Cbl deficiency, values for 2-methylcitric acid in serum ranged from 93 to 13,500 nmol/L; 44 (88%) had values above the normal range. In five patients with clinically confirmed Cbl deficiency, levels of the sum of 2-methylcitric acid I and II ranged from 1,370 to 16,300 nmol/L in CSF, and all five (100%) patients had levels above the normal range. We conclude that levels of 2-methylcitric acid are elevated in serum and CSF of most patients with Cbl deficiency.
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Affiliation(s)
- R H Allen
- Department of Medicine, University of Colorado Health Sciences Center, Denver 80262
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Hoffmann GF, Seppel CK, Holmes B, Mitchell L, Christen HJ, Hanefeld F, Rating D, Nyhan WL. Quantitative organic acid analysis in cerebrospinal fluid and plasma: reference values in a pediatric population. JOURNAL OF CHROMATOGRAPHY 1993; 617:1-10. [PMID: 8376520 DOI: 10.1016/0378-4347(93)80414-y] [Citation(s) in RCA: 28] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Quantitative reference values for the concentrations of organic acids in cerebrospinal fluid (CSF) and plasma, as well as ratios of individual organic acids between CSF and plasma, were determined in twenty-three pairs of samples from pediatric patients. Twenty-six organic acids were present and quantifiable in all or the majority of plasma and CSF specimens (limit of detection 1 mumol/l). There were substantial differences between subgroups of organic acids, best reflected by the ratios of individual acids between CSF and plasma. Metabolites related to fatty acid oxidation were present in CSF in substantially lower amounts than in plasma. Organic acids related to carbohydrate and energy metabolism and to amino acid degradation were present in CSF in equal or slightly lower amounts than in plasma. Finally, some organic acids were found in substantially higher amounts in CSF than in plasma, e.g. glycolate, glycerate, 2,4-dihydroxybutyrate, citrate and isocitrate. Quantitation of organic acids in CSF and plasma should aid diagnosis and monitoring of treatment of patients with organic acid disorders.
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Affiliation(s)
- G F Hoffmann
- Department of Pediatrics, University of California, San Diego 92093
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Vance GH, Moncino M, Heerema NA. Cytogenetic findings of a child with transcobalamin II deficiency. AMERICAN JOURNAL OF MEDICAL GENETICS 1993; 46:615-9. [PMID: 8362900 DOI: 10.1002/ajmg.1320460602] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Transcobalamin II deficiency is a rare, probably autosomal recessive, inborn error of protein metabolism [Hakami et al., 1971]. Several authors have described the morphological characteristics of bone marrow aspirates from patients with this disorder; no reports have detailed the cytogenetic findings [Hitzig et al., 1974; Hakami et al., 1971; Niebrugge et al., 1982]. We report the cytogenetic findings of the bone marrow aspirates from an infant with transcobalamin II deficiency and identify fragile site expression in the hematopoietic cells in this patient.
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Affiliation(s)
- G H Vance
- Department of Medical and Molecular Genetics, Indiana University, Indianapolis
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Abstract
A review of the clinical findings in six infants with nutritional vitamin B12 deficiency seen during the last 10 years was undertaken and an attempt made to obtain long-term neurologic follow-up. There was a consistent clinical pattern in vitamin B12-deficient infants; irritability, anorexia, and failure to thrive were associated with marked developmental regression and poor brain growth. Two of the four patients who qualified for long-term review had a poor intellectual outcome. Although early response to treatment is satisfying, the long-term consequences of nutritional vitamin B12 deficiency in infants emphasize the need for prevention or early recognition of this syndrome.
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Affiliation(s)
- S M Graham
- Prince of Wales Children's Hospital, Randwick, Australia
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