Vitamin B 12 Deficiency Diagnosis and Markers

Transcription

1 Vitamin B 12 Deficiency Diagnosis and Markers B. Fowler University Children's Hospital Basel (UKBB) Basel, Switzerland

2 Vitamin B 12 Deficiency Diagnosis and Markers Historical Background Biology and Genetic Disorders Deficiency states: Diagnosis and Markers

3 Vitamin B 12 Deficiency Diagnosis and Markers Historical Background

4 Vitamin B 12 Metabolism Timeline 1855 Addison described a remarkable form of anaemia "eating liver cures pernicious anaemia" 1948 Vitamin B 12 isolated 1956 Vitamin B 12 crystal structure elucidated 1960s Coenzymes for mammalian B 12 enzymes identified

5 Vitamin B 12 crystal structure

6 Vitamin B 12 crystal structure The molecule that appears is very beautifully composed, not far from spherical in form, with all the more chemically reactive groups on the surface Nobel Prize 1964

7 Vitamin B 12 Metabolism Timeline 1855 Addison described a remarkable form of anaemia "eating liver cures pernicious anaemia" 1948 Vitamin B 12 isolated 1956 Vitamin B 12 crystal structure elucidated 1960s Coenzymes for mammalian B 12 enzymes identified 1970s Inborn Errors of Vitamin B 12 metabolism discovered Classification of cbl defects/ complementation classes Bacterial B 12 enzymes mechanisms cloning of genes for B12 target enzymes Genes for intracellular B 12 "processing" 2000 à diagnostic Markers

8 Structure of Vitamin B 12 (Cobalamin, Cbl) In man essential cofactor for 2 enzymes Methionine Synthase Methyl-Cbl Adenosyl Methyl Co Methylmalonyl CoA-Mutase Adenosyl-Cbl

9 Foods rich in Vitamin B 12 (Cobalamin) Daily requirement 3µg Elderly??

10 Vitamin B 12 Deficiency Diagnosis and Markers Biology and Genetic Disorders

11 Vitamin B 12 and Homocysteine Metabolism Tetrahydrofolate Methionine Synthase MeCbl Methionine S-adenosyl methionine S-adenosyl homocysteine 5-Methyl-THF Cobalamin Homocysteine Serine Adenosine Cystathionine Cysteine Sulphate

12 Valine Isoleucine Methionine Threonine Odd-chain fatty acids Cholesterol Methylmalonic acid metabolism Cobalamin Propionyl-CoA D-Methylmalonyl-CoA Epimerase L-Methylmalony-CoA AdoCbl Mutase Succinate-CoA ADP Ligase ATP Succinyl-CoA Succinate GDP GTP α-ketoglutarate Fumarate free Methylmalonic Acid Isocitrate Malate Citrate Oxaloacetate Acetyl-CoA Pyruvate Lactate

13 Gastrointestinal Absorption of dietary Vit-B 12 Cbl = Cobalamin HC = Haptocorrinbound Cbl deg.hc = degraded HC IF = Intrinsic Factor IF-Cbl = IF-bound Cbl l -IF-Cbl = IF-Cbl attached to Cubilin (Ileal receptor) TCII-Cbl = Transcobalamin bound Cbl.

14 Haptocorrin def. Gastrointestinal Absorption of dietary Vit-B 12 Intrinsic Factor def. Cubilin / Amnionless def. Transcobalamin def. Cbl = Cobalamin HC = Haptocorrinbound Cbl deg.hc = degraded HC IF = Intrinsic Factor IF-Cbl = IF-bound Cbl l -IF-Cbl = IF-Cbl attached to Cubilin (Ileal receptor) TCII-Cbl = Transcobalamin bound Cbl.

15 Intracellular Cobalamin Metabolism Steps are defined by complementation classes Cytoplasm Methionine Cbl MeCbl Methionine Synthase OHCbl TC OHCbl TC Lysosome OHCbl Cbl Cbl Homocysteine Cbl AdoCbl Methylmalonyl-CoA Succinyl-CoA Methylmalonyl CoA-Mutase Mitochondrion

16 Intracellular Cobalamin Metabolism Steps are defined by complementation classes Cytoplasm OHCbl TC OHCbl TC Lysosome cblf OHCbl cblc Cbl cbld Cbl Cbl Methionine cble MeCbl cblg Homocysteine cbla Cbl cblb AdoCbl Methylmalonyl-CoA Succinyl-CoA mut Mitochondrion

17 New Genes The CblC defect NATURE GENETICS 38 I NUMBER1 I JANUARY Discovered by homozygosity mapping Located on chromosome 1p Codes for approx. 30 kda protein

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19 New Genes: The CblD defect one gene three phenotypes combined defect methylmalonic-aciduria / homocystinuria isolated Hcy isolated MMA Significant homology with bacterial genes related to ABC transporters Encodes a polypeptide of 296 aminoacids (32.8 kda) Mutations were found in all cbld patients MethylMalonic Aciduria and HomoCystinuria cbld type (MMADHC) Maps to chromosome 2q23.2

20 New Genes: the cblf defect 2009: 41;234 Mutations in the LMBRD1 gene (encoding LMBD1, a lysosomal membrane protein) found in cblf patients G 78 N-terminus G 88 G 170 No. 2 T172fs No. 5 L352fs G G G Intralysosomal cytosolic G No. 1 T134fs No. 3 T237X 540 No. 4 C-terminus K281fs Site of mutation (fs = frameshift) Putative glycosylation site

21 A new Cbl complementation class mimicking cblf is caused by mutations of ABCD4 Coelho D et al. Basel, Zürich, colleagues from Montreal, Münster Late breaking news SSIEM 2011, Geneva Two patients with cblf phenotype but new complementation group N. American case European case whole exome capture microcell mediated chromosome transfer à 2 mutations of ABCD4 exome sequencing of chr. 14 ABCD4 presumed ABC transporter à 2 other mutations of ABCD4

22 Coelho D, Suormal T, Stucki M, Lerner-Ellis JP, Rosenblatt DS, Newbold R, Baumgartner M, Fowler B. N ENGL J MED 358;14 APRIL 3, 2008 TCR cblj cbld- balance weak MLS

23 Vitamin B 12 Deficiency Diagnosis and Markers Deficiency states Diagnosis and Markers

24 Cobalamin and common diseases Vitamin B 12 deficiency in breastfed Newborns - mothers on vegan diet / B 12 absorption problems Mal-absorption of cobalamin especially in elderly persons

25 Causes of Cobalamin Malabsorption Causes often leading to megaloblastic anemia Autoimmune Gastric Intestinal - Pernicious anemia - Congenital IF deficiency - Gastrectomy - Congenital transcobalamin deficiency - Selective malabsorption with proteinuria (MGA1; Imerslund Gräsbeck syndrome) - Intestinal stagnant loop syndrome: jejunal diverticulosis, ileocolic fistula, anatomical blind loop, intestinal structure, etc. - Ileal resection and Crohn s disease - Tropical sprue - Fish tapeworm

26 Causes of Cobalamin Malabsorption Causes usually NOT leading to megaloblastic anemia Gastric Intestinal Nutritional - Simple atrophic gastritis (food B 12 malabsorption) - Zollinger-Ellison syndrome - Gastric bypass surgery - Use of proton pump inhibitors - Gluten-induced enteropathy - Severe pancreatitis - HIV infection - Radiotherapy - Graft versus host disease - Deficiencies of B 12, folate, protein Drugs - Colchicine Para-aminosalicylate - Neomycin Slow-release potassium chloride - Anticonvulsant drugs Metformin - Phenformin Cytotoxic drugs - Alcohol

27 Vitamin B 12 Deficiency Diagnostics & Markers: Different levels Clinical Symptoms, Haematological changes - example: Child of a Veganer Nutritional - Dietary History - Total B 12 in Blood (Haptocorrin + Transcobalamin) Active transport form - Holo-transcobalamin Metabolic Function level - Methylmalonic acid (MMA), total Homocysteine Caveat: kidney function Enzyme level - fibroblast assays - severe genetic disorders Genetic level - mutations in severe genetic disorders - polymorphhisms in common conditions

28 Vitamin B 12 Deficiency Total homocysteine mean Homocysteine concentration µmol/l Selhub et al. JAMA 1993;270:

29 Vitamin B 12 -Deficiency in 8 Month old child of a Vegetarian (part of small intestine removed) Clinical Lab findings increasing tiredness over 4 weeks Apnea, Hypotonic, Myoclonic episodes µmol/l Child Homocysteine Mother Normal Kind Mutter Normal Treatment B µg/d i.m. Homocysteine normal

30 Markers for Vitamin B 12 disturbance in common diseases Plasma (Urine) Methylmalonic acid Method - Gas Chromatography / Mass Spectrometry - Extraction Stable isotope dilution using D3 - Methylmalonic acid as carrier and internal standard cut off ca. 300 nmol/l Accurate / sensitive but time consuming / expensive equipment

31 MMA Stable Isotope Dilution: B 12 deficiency MMA 1.1 µmol/l D3-MMA

32 Vitamin B 12 Deficiency Plasma Methylmalonic acid Allen et al. FASEB J Nov;7(14):

33 Markers for Vitamin B 12 disturbance Plasma Holo-transcobalamin (B 12 bound to transcobalamin) transcobalamin

34 Markers for Vitamin B 12 disturbance Plasma Holo-transcobalamin (B 12 bound to transcobalamin) Previous assays unreliable and cumbersome Recent methods precise and accurate (e.g. Ueland et al. 2002) - separation of trans-cobalamin by monoclonal antibody à B 12 measured by radio-assay - monoclonal antibody for HOLO-transcobalamin in chemiluminescence assay Commercially available assays

35 Plasma Holo-transcobalamin as Marker for Vitamin B 12 disturbance Holotranscobalamin as a Predictor of Vitamin B 12 Status Anne-Metter Hvas and Ebba Nexo Clin Chem Lab Med 2003; 41(11): Holo- transcobalamin, a marker of vitamin B- 12 status: analytical aspects and clinical utility Ebba Nexo and Elke Hoffmann-Lücke Am J Clin Nutr 2011;94:359S-365S

36 Cobalamin and its binding proteins in human plasma by American Society for Nutrition Nexo E, Hoffmann-Lücke E Am J Clin Nutr 2011;94:359S

37 Holotranscobalamin (holotc) and cobalamin in relation to methylmalonic acid Haptocorrin bound B 12 holotc Total B 12 AUC (vs. MMA) Total B12 ca. 80% HoloTC ca. 90% Haptocorrin bound B 12 holotc 2011 by American Society for Nutrition Nexo E, Hoffmann-Lücke E Am J Clin Nutr 2011;94:359S

38 Non-radioactive Vitamin B 12 Absorption Test Controls and Patients with Inherited Malabsorption of Vitamin B 12 Change after B 12 intake* Day 1 - Day 0 * 3 x 9µg oral B 12 6 hourly Bor et al. Clin Chem 2005; 51:2151

39 Markers for Vitamin B 12 disturbance: Summary Limitations of individual analyte assays indicate that no single assay is completely adequate for assessment of B 12 status. Novel or refined strategies using sequential tests in an algorithm proposed for diagnosis or detection of B 12 deficiency or for screening populations. Strategies promote panels of two or more measurements performed in sequence or simultaneously

40 Measure chosen parameters / e.g. haptocorrin then MMA If still unclear contact expert

41 Clinical situation Measure chosen parameters / e.g. haptocorrin then MMA If still unclear contact expert

42 Acknowledgements Terttu Suormala, David Coelho (Basel), Matthias Baumgartner, Martin Stucki (Zürich) Jordan Lerner-Ellis, David Rosenblatt (Montreal) Petra Zavadakova, Viktor Kožich (Prague) Hans Georg Koch, Martin Berghäuser (Münster) James E. Wraith (Manchester), Alberto Burlina (Padua) Adrian Sewell, Jürgen Herwig (Frankfurt) Many colleagues who sent us fibroblasts Swiss National Science Foundation grant No

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