Vit B12 and folic acid deficiency

Question 1

What is the alternative name for vit B12?

Answer 1

Cobalamin

Question 2

What is the role of VitB12?

Answer 2

DNA synthesis

Maintaining nervous system integrity (involved in myelination)

Question 3

What is the main dietary source of folic acid?

Answer 3

Leafy greens

Question 4

What is the role of folic acid in haematopiesis?

Answer 4

DNA synthesis

Question 5

What is the role of folic acid and B12 in biochemical pathways in the body?

Answer 5

Homocysteine metabolism to methionine

Question 6

What is the main consequence of defective homocysteine metabolism?

Answer 6

CVD (main increased risk)
Venous/Arterial thrombosis

Homocysteine aggravates atherosclerosis and premature vascular diseases, leading to the above 2 problems

Question 7

What roles do vit B12 and folic acid play in DNA synthesis?

Answer 7

dTMP synthesis:

B12 acts as a cofactor for methionine synthetase

Question 8

Recall some dietary sources of B12

Answer 8

Meat, salmon, cod, dairy products, eggs

Question 9

How is B12 absorbed?

Answer 9

Method 1: straight through Duodenum (slow and inefficient)

Method 2: Most common method

1. Binds to IF in stomach produced by parietal cells
2. B12-IF complex binds to receptors in terminal ileum
3. Absorbed

Question 10

Recall the full pathway of folic acid absorption

Answer 10

Hydrolysed in stomach due to low pH –> monoglutamates

Absorbed as pteroglutamates

Question 11

Recall 3 causes of B12 deficiency
Diet
Malabsorption
Infections
Drugs

Answer 11

Diet: Vegan diet
Malabsorption: pernicious anaemia, GI surgery, coeliac disease, Crohn’s
Infections: H pylori, Giardia
Drugs: Metformin, oral contraceptives, PPI eg omeprazole

Question 12

Recall 3 reasons why folic acid absorption might be impaired

Answer 12

Coeliac
IBD
Drugs

Question 13

Recall 3 physiological and 3 pathological reasons why folic acid demand would be increased

Answer 13

PHYSIOLOGICAL
Pregnancy
Adolescence- period of rapid growth
Premature babies- grow quickly and they can become deficient of Folate
PATHOLOGICAL
Malignancy- turnover of extra cells
Erythoderma – massive turnover of skin cells
Haemolytic anaemias – increased RBC turnover

Question 14

What sorts of anaemia are caused by B12 deficiency?

Answer 14

B12 deficiency will lead to Macrocytic and megaloblastic erythrocytes. It is called pernicious anaemia if the B12 deficiency is caused by Autoimmune attack on parietal cells which produce IF

Question 15

Other than anaemia, what is a key clinical feature of B12 deficiency?

Answer 15

Neurological problems due to demyelination
eg
-Bilateral peripheral neuropathy
-Subacute combined degeneration of the cord
-optic atrophy
- dementia

Question 16

Describe the shape of macrocytes in vit B12/ folic acid deficiency

Answer 16

oval

Question 17

How is the MCV affected by megaloblastic aneamia and why?

Answer 17

Drops

Morphological change of erythrocyte within bone marrow

Question 18

Why are red cell precursors increased in sixe in megaloblastic anaemia?

Answer 18

Defects in DNA synthesis –> asynchronous maturation of cytoplasm and nucleus

Question 19

What is the origin of hypersegmented neutrophils?

Answer 19

Giant metamyelocytes in bone marrow due to defective DNA synthesis

Question 20

What would be seen alongside erythrocytes in the blood film of someone with B12 deficiency?

Answer 20

Fragments of red cells

Question 21

What is the gold standard test for diagnosis of B12/ folic acid deficiency, and what is a positive result?

Answer 21

Plasma homocysteine

High

Question 22

How can B12 deficiency be treated?

Answer 22

Injections