Vitamin B12 and Folic Acid Deficiency

Question 1

What is vitamin B12 and what types of food is it commonly found in?

Answer 1

Cobalamin (vitamin B12) is a bacterial product that is ingested and stored by animals.
It is found in meat, cheese, salmon, cod, milk, eggs

Question 2

How much B12 is needed every day and how much is found in hepatic stores?

Answer 2

1.5-3 mcg/day required

Store: 2-5 mg (will last several years)

Question 3

What is Vitamin B12 needed for?

Answer 3

DNA synthesis

Integrity of the nervous system (involved in myelination)

Question 4

Broadly speaking, what can cause Vitamin B12 deficiency?

Answer 4

Dietary deficiency (vegans) 
Decreased absorption

Question 5

What types of food have lots of folic acid?

Answer 5

Leafy green vegetables

Question 6

Broadly speaking, what can cause folic acid deficiency?

Answer 6

Dietary deficiency
Increased demand for folate
Impaired absorption

Question 7

What is the dietary requirement of folic acid?

Answer 7

400-600 mcg

You run out of folate much quicker than B12

Question 8

What is folic acid required for?

Answer 8

DNA synthesis

Homocysteine metabolism

Question 9

Describe the passage of vitamin B12 from entry into the GI tract tothe hepatic portal circulation.

Answer 9

It enters the stomach and binds to transcobalamin 1 (R protein –produced by the salivary glands)
The gastric parietal cells (at the bottom of the stomach) produce intrinsic factor
The B12 moves into the duodenum, bound to transcobalamin 1, and then pancreatic enzymes displace B12 from transcobalamin 1 The free B12 then binds to intrinsic factor
The B12-intrinsic factor complex continues all the way to the terminal ileum where it binds to specific receptors and is absorbed The B12 then goes into the portal circulation and binds to transcobalamin 2 making active B12

Question 10

Describe the absorption of folic acid.

Answer 10

Folic acid enters the GI tract as polyglutamates
The acidic pH of the stomach hydrolyses the polyglutamates to monoglutamates
The folic acid is absorbed as pteroglutamates
It is then methylated in the luminal cells to form methyl tetrahydroflorate

Question 11

Deoxythymidine (dTMP) is a major building block of DNA synthesis. How is it produced?

Answer 11

It is produced by the methylation of deoxyuridine (dUMP)
For the methylation to take place, you need the release of methyl groups from methyl-tetrahydrofolate by the action of B12 as a cofactor accompanied by the conversion of homocysteine to methionine.

Question 12

In what reaction is B12 a co-factor?

Answer 12

The conversion of homocysteine to methionine

Enzyme = methionine synthetase

Question 13

State some clinical features of B12 and folate deficiency.

Answer 13

Anaemia (macrocytic and megaloblastic) 
Jaundice (due to ineffective erythropoiesis) 
Angular Cheilosis  
Glossitis  
Sterility  
Weight loss and change of bowel habit

Question 14

State some causes of macrocytic anaemia.

Answer 14

Vitamin B12/Folate deficiency
Liver disease and alcoholism
Hypothyroidism
Haematological disorders:
 Myelodysplasia (production of one or all types of blood cells by the bone marrow is disrupted)
 Aplastic anaemia (failure of blood cell production resulting in pancytopenia)
 Reticulocytosis (in response to haemolytic anaemia or bleeding)
Drugs that interfere with DNA synthesis
Prolonged nitrous oxide anaesthesia

Question 15

How can you differentiate between the blood film of someone with B12/Folate deficiency and someone with liver disease or alcoholism causing macrocytosis?

Answer 15

B12/Folate deficiency = OVAL macrocytes

Liver disease and alcoholism = ROUND macrocytes

Question 16

What is a reticulocyte?

Answer 16

A young red blood cell with no nucleus

Question 17

Describe how the appearances of cells of the red cell lineage change as they mature.

Answer 17

They become smaller and their cytoplasm becomes pinker
Their nucleus starts off being quite diffuse (open chromatin) and it becomes more and more compact until it is spit out by the red cell

Question 18

Given your previous answer, what two things do you look at when determining the maturity of a red blood cell?

Answer 18

Chromatin – how open is it?

Colour of the cytoplasm – how blue is it?

Question 19

What is meant by ‘megaloblastic changes’?

Answer 19

These are changes seen in the red blood cell precursors in the bone marrow.
Megaloblastic change is when there is asynchronous maturation of the nucleus and cytoplasm.
You get an immature, open nucleus with mature cytoplasm.

Question 20

Broadly speaking, what are megaloblastic changes the result of?

Answer 20

Defective DNA synthesis

Question 21

Which of the causes of macrocytic anaemia also show megaloblastic changes in the bone marrow?

Answer 21

B12/Folate deficiency
Myelodysplasia
Drugs that interfere with DNA synthesis
Prolonged nitrous oxide anaesthesia

Question 22

In megaloblastic anaemia, you see changes in the red blood cellsand the white blood cells. Describe these changes.

Answer 22

Red blood cells
 Asynchrony between maturation of nucleus and cytoplasm (immature nucleus and mature cytoplasm)
 Increase in size of red cell precursors at all stages of maturation
 Increase in bone marrow activity because haemopoiesis is ineffective (dysplastic)
 Phagocytosis of dysplastic red blood cells
White blood cells
 Giant metamyelocytes (due to asynchronous maturation)
 Hypersegmented neutrophils

Question 23

Which groups are at particular risk of dietary folate deficiency?

Answer 23

Elderly, sick, eating disorders, alcoholics

Question 24

What are the consequences of folate deficiency for DNA synthesis?

Answer 24

Folate deficiency means that you can’t methylate dUMP to dTMP, which affects DNA synthesis.
It also leads to the accumulation of homocysteine (it can’t be converted to methionine without folate)

Question 25

State some physiological and pathological causes of increased folate demand.

Answer 25

Physiological (increased growth) 
 Pregnancy
 Adolescence 
 Premature babies
Pathological (rapid cell turnover) 
 Malignancy 
 Erythroderma (whole body rash)
 Haemolytic anaemia

Question 26

State some causes of malabsorption of folate.

Answer 26

Coeliac Disease
Surgery or inflammatory bowel disease (e.g. Crohn’s disease)
Drugs (e.g. colestyramine, sulfasalazine and methotrexate)

Question 27

What is coeliac disease caused by?

Answer 27

Sensitivity to gliadin (group of proteins found in wheat) leads to subtotal villous atrophy with crypt hyperplasia in the duodenum.

Question 28

How can coeliac disease be diagnosed?

Answer 28

Anti-gliadin (transglutaminase) antibodies

Duodenal biopsy

Question 29

State some tests to identify folate deficiency.

Answer 29

Full blood count
Blood film
Serum folate – useful as a screening test
 Shows diurnal variation
 Affected by recent changes in diet
Red cell folate – useful as confirmatory test

Question 30

What would you expect the serum folate and red cell folate of a patient with B12 deficiency to be and why?

Answer 30

Serum folate = high
Red cell folate = LOW
This is because B12 is required for the folate to enter the red blood cells

Question 31

What are the three main consequences of folate deficiency?

Answer 31

Megaloblastic anaemia
Neural tube defects
Increased risk of venous thromboembolism

Question 32

What are the two types of neural tube defects?

Answer 32

Spinal cord = spina bifida

Brain = anencephaly

Question 33

What are the NICE guidelines for women of standard and high risk of neural tube defects?

Answer 33

Standard Risk – 400 mcg folic acid preconception to 12 weeks gestation
High Risk – 5 mg folic acid preconception to 12 weeks gestation
Haemolytic anaemia – 5-10 mg before, during and after pregnancy

Question 34

Homocysteine accumulates in folate deficiency. What are the consequences of this?

Answer 34

Very high homocysteine levels are associated independently with:
 Atherosclerosis
 Premature vascular disease
Mildly elevated homocysteine is associated with cardiovascular disease and probably with arterial and venous thrombosis.

Question 35

How did the FDA in the USA attempt to reduce the incidence of NTDs due to folate deficiency?

Answer 35

Fortify grain with folate

Question 36

Which groups of people are at particular risk of vitamin B12 deficiency due to decreased intake?

Answer 36

Vegans

Question 37

State some factors that can affect the absorption of B12.

Answer 37

Autoimmune – pernicious anaemia (lack of intrinsic factor)
Surgery – resection of parts of the GI tract
Inflammatory bowel conditions – Crohn’s, chronic pancreatitis, bacterial overgrowth, parasitic infection

Question 38

What are the two main consequences of B12 deficiency?

Answer 38

Macrocytic and megaloblastic anaemia
Neurological problems due to demyelination
 Subacute combined degeneration of the spinal cord
 Neuropathy of central and peripheral nerves
 Cognitive impairment due to loss of white matter in the CNS
 Optic atrophy

Question 39

What is the relationship between Hb level and neurological symptoms in B12 deficiency?

Answer 39

Inverse relationship between Hb level and neurological symptoms

Question 40

What is subacute combined degeneration of the spinal cord and what are the symptoms?

Answer 40

Caused by demyelination of the posterior (dorsal) and lateral (pyramidal) tracts of the cervical and thoracic spinal cord
Results in loss of joint position sense and vibration sense.
Patient may have a wide-based gait and sometimes experience pain.

Question 41

State some symptoms and signs of B12 deficiency.

Answer 41

Weak, tired, lethargic
Symmetrical parasthesia/numbness
Muscle weakness
Difficulty walking and loss of balance
Anaemia and jaundice giving ‘yellow tinge’
Neurology
 Loss of vibration and joint position sense but also cutaneous sensation loss
 Absent responses and up-going plantar responses in legs
Visual impairment
Memory impairment
Psychiatric disturbance

Question 42

What is the test for B12 deficiency?

Answer 42

Serum cobalamin (B12) level PROBLEM: it measures total cobalamin levels (bound to transobalamin 1, 2 and 3) so you see a lot of healthy patients with low transcobalamin  
This means that the clinical circumstances must be taken into account when interpreting the results.

Question 43

What is the role of B12 in DNA synthesis?

Answer 43

Both B12 and folate are needed for the production of dTMP (deoxythymidine), which is a crucial building block in DNA synthesis

Question 44

State some new tests used to diagnose B12 deficiency.

Answer 44

Plasma homocysteine (high in B12 and folate deficiency) 
Serum methyl malonic acid levels  
Holotranscobalamin levels (transcobalamin II)

Question 45

What is the Schilling test for B12 absorption?

Answer 45

Give two capsules of B12 with different radioisotopes.
1 capsule will be B12 alone
1 capsule will be B12 + intrinsic factor
Collect urine for 24 hours after administration and measure the presence and relative proportion of each isotope.

Question 46

What is pernicious anaemia and what does it result in?

Answer 46

A form of anaemia resulting from the deficiency of B12
It can be caused by autoimmune atrophic gastritic with the loss of intrinsic factor
This results in macrocytic/megaloblastic anaemia with or without neurological damage

Question 47

Which antibodies are found in pernicious anaemia?

Answer 47

Anti-intrinsic factor antibodies (in 40-60% of adults with PA)
Anti-gastric parietal cell antibodies (in 80-90% of adults with PA)

Question 48

How are folate and B12 deficiency treated?

Answer 48

Oral folate or oral cyanobalamin for dietary deficiency or increased demand
Parenteral (IM/SC) hydroxycobalamin for malabsorption due to pernicious anaemia or bowel disease