B12 and Folate Deficiency

Question 1

What are Vitamin B12 and Folate required for?

Answer 1

B12 required for DNA synthesis and Nervous system integrity (involved in myelination)

Folate required for DNA synthesis and homocystine metabolism

Question 2

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

Answer 2

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 3

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

Answer 3

1.5-3 mcg/day required Store: 2-5 mg (will last several years)

Question 4

What types of food have lots of folic acid?

Answer 4

Leafy green food

Question 5

What is the dietary requirement of folic acid?

Answer 5

400-600 mcg You run out of folate much quicker than B12

Question 6

Broadly speaking, what can cause Vitamin B12 and folate deficiency?

Answer 6

B12
Dietary deficiency (vegans)
Decreased absorption

Folate
Dietary deficiency

Increased demand ( pregnancy, adolescence, premature babies, malignancy, erythroderma, haemolytic anaemias)

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

Question 7

Describe the passage of vitamin B12 from entry into the

Answer 7

GI tract to the hepatic portal circulation.
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 IF
The B12-IF 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

NOTE: 1% IS ABSORBED ACROSS DUODENUM WITHOUT IF

Question 8

Describe the absorption of folic acid.

Answer 8

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 9

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

Answer 9

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 10

In what reaction is B12 a co-factor?

Answer 10

The conversion of homocysteine to methionine

Enzyme = methionine synthetase

Question 11

State some clinical features of B12 and folate deficiency.

Answer 11

All rapidly dividing cells affected by deficiency

• bone marrow
• Mouth and gut epithelium
• Gonads (SPERM ESPECIALLY)
• Embryos

Clincal features

• Anaemia, weak and fatigued
• Jaundice
• Glossitis (inflamed tongue) and angular cheilosis (corner of mouth inflammation)
• Weight loss, bowel habit changes
• Sterility

Anaemia will be macrocytc and megaloblastic

Question 12

State some causes of macrocytic anaemia.

Answer 12

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 e.g Azathioprine (immunosuppresant)
Prolonged nitrous oxide anaesthesia

Question 13

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

Answer 13

B12/Folate deficiency = OVAL macrocytes

Liver disease and alcoholism = ROUND macrocytes

Question 14

What is a reticulocyte?

Answer 14

A young red blood cell with no nucleus

Question 15

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

Answer 15

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 16

What two things do you look at when determining the maturity of a red blood cell?

Answer 16

Chromatin – how open is it?

Colour of the cytoplasm – how blue is it?

Question 17

What is meant by ‘megaloblastic changes’?

Answer 17

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.

Other findings (also due to DNA synthesis failures)
Anisocytosis
Large red cells
Hypersegmented neutrophils
Giant metamyelocytes
Dysplastic marrow and increased haemolysis

Question 18

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

Answer 18

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

Question 19

Which groups are at particular risk of dietary folate deficiency?

Answer 19

Elderly
Sick
Eating disorders
Alcoholics

Question 20

What are the consequences of folate deficiency for DNA synthesis?

Answer 20

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 21

State some tests to identify folate deficiency.

Answer 21

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

Also Anti-gliadin (transglutaminase) antibodies and Duodenal biopsy can diagnose coeliac as cause of malabsorption

Question 22

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

Answer 22

Serum folate = high
Red cell folate = LOW

This is because B12 is required for the folate to enter the red blood cells

Question 23

What are the three main consequences of folate deficiency?

Answer 23

Megaloblastic anaemia
Neural tube defects - Spina bifeda, anencephaly in foetus
Increased risk of venous thromboembolism - due to various enzymes in homocystein metabolism

Question 24

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

Answer 24

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 25

State some factors that can affect the absorption of B12.

Answer 25

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 26

What are the two main consequences of B12 deficiency?

Answer 26

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 27

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

Answer 27

Inverse relationship between Hb level and neurological symptoms

Question 28

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

Answer 28

Caused by demyelination of the posterior (dorsal) and lateral (pyramidal) tracts of the cervical and thoracic spinal cord

Question 29

How do B12 deficient patients present?

Answer 29

• Paraethesiae
• Myopathy
• Walking difficulty
• Visual impairment
• Psychiatric distrubance
• Romberg’s sign (loss of propriception)
• Anaemia and Jaundice

Examination finding

• Loss of peripheral reflex
• Babinski’s sign

Question 30

What is the test for B12 deficiency?

Answer 30

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 31

State some new tests used to diagnose B12 deficiency.

Answer 31

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

Question 32

What is the Schilling test for B12 absorption?

Answer 32

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 33

What is pernicious anaemia and what does it result in?

Answer 33

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 34

Which antibodies are found in pernicious anaemia?

Answer 34

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

Question 35

How are folate and B12 deficiency treated?

Answer 35

Oral folate or oral cyanobalamin for dietary deficiency or increased demand

Parenteral (IM/SC) hydroxycobalamin for malabsorption due to pernicious anaemia or bowel disease