1. B-12 AND FOLATE DEFICIENCY MEGALOBLASTIC ANEMIAS

2. MACROCYTIC VS MEGALOBLASTIC ANEMIA
Macrocytic: MCV >95-100
Megaloblastic:
delayed nuclear maturation

3. MACROCYTIC VS MEGALOBLASTIC ANEMIA
Causes of macrocytosis
Liver disease
Alcoholism
Reticulocytosis
Hypothyroidism
Aplastic anemia
Myelodysplasia
Drugs that block DNA synthesis
B-12 and folate deficiency
Megaloblastic

4. Circulating megaloblast
Circulating normoblast
Megaloblastic eosinophil
Peripheral blood: oval macrocyte, hypersegmented PMN

5. Normal erythroid precursors
Bone marrow: giant band (black arrow), megalobasts at various stages of differentiation (red arrows)

6. megalo
normal

7. B12 deficiency → increased homocysteine and methylmalonate
Folate deficiency → increased homocysteine

8. Tetrahydrofolate required for thymidine synthesis and hence for DNA synthesis
B-12 deficiency “traps” folate in methylTH4 form, unavailable for thymidine synthesis

9. Enzymatic reactions that use folates. BG Katzung, SB Masters, AJ Trevor. Basic and Clinical Pharmacology, 12th edition (2012)

10. VITAMIN B-12
Dietary sources: meat, poultry, fish; typical intake 7-30 μg/day, 2-3 μg absorbed
Stomach acid enhances absorption from food; intrinsic factor (from gastric parietal cells) facilitates absorption in ileum
Absorbed vitamin bound to transcobalmin II and transported to marrow
Normal body stores μg (biologic half-life about 1 yr)
Clinical disease associated with B-12 deficiency when stores < 20% of normal

11. B-12 Absorption NO INTRINSIC FACTOR → ↓↓ B-12 ABSORPTION
Dietary B-12 transferred from food to binding protein (R-binder or haptocorrin) in stomach. Stomach acid needed.
Intrinsic factor (IF) made by gastric parietal cells
Pancreatic enzymes degrade R-binders in duodenum; B-12 transferred to IF
B-12/IF complex binds to receptor (cubulin) in distal ileum
B-12 absorbed, IF broken down
NO INTRINSIC FACTOR → ↓↓ B-12 ABSORPTION

12. Blood 2017;129:2603

13. CAUSES OF B-12 DEFICIENCY
Insufficient intake (strict vegetarians/vegans)
Failure of absorption
Lack of intrinsic factor: autoimmune (“pernicious anemia”), gastrectomy, (rare) inherited deficiency of IF
Pancreatic insufficiency (rare cause)
Lack of ileal absorption: Crohn’s, small bowel resection
Competition for vitamin by intestinal bacteria (eg “blind loop” syndrome) or tapeworm
Genetic lack of transcobalmin II (rare)
Destruction of B-12 by nitrous oxide

14. Autoimmune destruction of parietal cells causes B-12 deficiency
3. T-cells kill parietal cells, no intrinsic factor or acid produced
1. Dendritic cells in stomach clear apoptotic parietal cells
2. Dendritic cells in paragastric nodes activate T-cells directed against ATPase expressed in parietal cells
NEJM 2014;370:773

15. Hematologic improvement with liver extract (lots of B-12) or “stomach juice” (source of intrinsic factor) given orally in patients with pernicious anemia
Castle WB. Am J Med Sci 1929 (from NEJM 2014;370:773)

17. AUTOIMMUNE DEFICIENCY OF B-12 “PERNICIOUS ANEMIA”
Antibodies to parietal cells (sensitive test)
Antibodies to intrinsic factor (specific test)
Permanent loss of B-12 absorption
Achlorhydria, gastric atrophy (not corrected by B-12 replacement)

18. B-12 DEFICIENCY BLOOD AND MARROW FINDINGS
Megaloblastic anemia
WBC and platelets may be low (pancytopenia)
Low serum B-12 level, increased methylmalonate and homocysteine
Marrow cellular with low G:E ratio, megaloblastic changes in rbc and granulocyte series
Retic count not increased (ineffective erythropoiesis)
High LDH and bilirubin due to red cell precursor breakdown in marrow (in advanced disease)

19. Hypercellular marrow, erythroid hyperplasia, megaloblastic erythropoiesis, giant band (arrow)
Normal marrow

20. B-12 DEFICIENCY OTHER CONSEQUENCES
Neurologic injury (esp loss of vibratory sense & proprioception)
Advanced disease may not be completely reversible
Giving folate to B-12 deficient pt may correct/prevent anemia, but make neurologic deficits worse
Neural tube defects (in pregnancy)
Glossitis

21. Figure 4.4. Degeneration of the posterior and lateral columns of the spinal cord in vitamin B12 deficiency. The arrows point to areas of demyelination and loss of nerve fibers. (From Kass, LS: Pernicious anemia. Phila., WB Saunders Co., 1976.)

22. B-12
December 1982
April 1983
Courtesy of Dr. Robert Schilling

23. FOLIC ACID
MW 400
Yeast, vegetables, dairy products, seafood good dietary sources (but vitamin can be destroyed by cooking)
Absorbed in jejunum (50-80% of dietary vitamin absorbed)
Normal intake mcg/day, requirement 100 mcg/day
Body stores mg
Biologic half-life about one month
Stores can be depleted if RBC production demand high
Needed for thymidine synthesis, amino acid metabolism, purine metabolism

24. FOLATE DEFICIENCY Causes
Poor diet
Celiac disease
Pregnancy (increased utilization)
Increased rbc production (chronic hemolysis – increased utilization)
Alcoholism (poor diet, poor absorption, poor storage if liver injured)
Anticonvulsants (phenytoin) decrease absorption

25. FOLATE DEFICIENCY Clinical and laboratory findings
Megaloblastic anemia with ineffective erythropoiesis (typically less severe than advanced B-12 deficiency)
WBC and/or platelets may be low
No neurologic injury
Mild maternal deficiency → neural tube defects
Low serum folate level
RBC folate level does not provide additional useful information
Increased serum homocysteine, normal methylmalonate

26. B-12 AND FOLATE DEFICIENCY
Cause
B-12
Folate
Decreased intake
Strict vegetarians and vegans
Alcoholism
Malnutrition
Malabsorption
Absence of intrinsic factor
Blind loop
Pancreatic insufficiency
Resection of terminal ileum
Drugs
Generalized malabsorption
Increased utilization/loss
Very rare
Pregnancy
Hemolysis
Drug inhibition
Nitrous oxide
Methotrexate
Genetic defects
Transcobalmin II (rare)
Even rarer