Vitamin B12 and folic acid deficiency Flashcards
What are the roles of B12 and folate
Required for DNA synthesis
Absence leads to severe anaemia which can be fatal
In the olden days someone with pernicious anaemia would just gradually get more anaemic and just fade away.
What is B12 required for
. DNA synthesis
2. Integrity of the nervous system
What is folic acid required for
DNA Synthesis
Homocystine metabolism
Deoxythymidine (dTMP) is a major building block of DNA synthesis. How is it produced?
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.
dUMP – dTMP
dTMP – dTDP – dTTP
dietary folate absorbed by the small intestine is converted to methyl-THF
methyl-THF- THF (Vit B12 converts homocysteine to methionine)
THF- THF-Polyglutamate
THF-POlyglutamate — 5,10 methylene THF- polyglutamate (donates methyl group to dUMP)
This needs to be recycled
so it is converted to DHF-polyglutamate which is converted back to THF- polyglutamte upon consumption of folic acid.
In what reaction is B12 a co-factor
The conversion of homocysteine to methionine
Enzyme = methionine synthetase
What cells are affected in B12 and folate deficiencies
ALL RAPIDLY DIVIDING CELLS ARE AFFECTED Bone marrow Epithelial surfaces of mouth and gut Gonads embryos
Describe the clinical features of B12 and folic acid deficiency
Anemia: weak, tired, short of breath Jaundice Glossitis (inflammation of tounge) and angular cheilosis (red swollen patches at corner of mouth) Weight loss, change of bowel habit Sterility
What anaemia is caused by B12 and folic acid deficiency
ANEMIA
This is macrocytic and megaloblastic
What is meant by macrocytic
Average red cell size is above the normal range
Describe the different causes of macrocytic anaemia
Vitamin B12/folate deficiency Liver disease or alcohol Hypothyroid Drugs e.g. azathioprine Haematological disorders: Myelodysplasia, aplastic anemia Reticulocytosis e.g. chronic haemolytic anemia · 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) Drugs that interfere with DNA synthesis Prolonged nitrous oxide anaesthesia
What is meant by megaloblastic
Describes a morphological change in the red cell precursors within the bone marrow
Summarise normal red cell maturation
Erythroblast
Normoblast: early/intermediate/late
Reticulocyte
Circulating red blood cell
proerythroblast basophilic erythroblast polychromatic erythroblast pyknotic erythroblast reticulocyte mature red cell
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 (pyknotic stage)
Describe megaloblastic changes
Defined by asynchronous maturation of the nucleus and cytoplasm in the erythroid series.
Maturing red cells seen in the bone marrow
You get an immature, open nucleus with mature cytoplasm
These are changes seen in the red blood cell precursors in the bone marrow.
Broadly speaking, what are the megaloblastic changes as a result of
Defective DNA synthesis
What may be seen on the peripheral blood in megaloblastic anaemia
Anisocytosis Large red cells Hypersegmented neutrophils Giant metamyelocytes May see bridging nuclei between two red cells
What are the causes of macrocytic anaemia that also show megaloblastic changes in the bone marrow
B12/Folate deficiency
Myelodysplasia
Drugs that interfere with DNA synthesis
Prolonged nitrous oxide anaesthesia
Give 3 tests that you would do if someone had a macrocytosis
Thryoid tests
B12/Folate
LFTs
Where can dietary folate be obtained from
Fresh leafy vegetables
Destroyed by overcooking/canning/processing
What are the main causes of decreased intake of dietary folate
IGNORANCE
POVERTY
APATHY
……..consider - elderly -alcoholics
Describe the physiological and pathological causes of increased folate demand
PHYSIOLOGICAL
Pregnancy
Adolescence
Premature babies
PATHOLOGICAL
Malignancy
Erythoderma (reddening of skin- total body eczema or psoriasis)
Haemolytic anaemias
Describe some classic cases in which folic acid can present
alcoholic admitted with a head injury after a fight
30y old lady with infected whole body eczema
90 y old lady who has a cup of tea and a jam sandwich for each meal
Describe the laboratory diagnosis of folate deficiency
FBC and film
Folate levels in the blood
Describe how we can assess the cause of a folate deficiency
EASY – history (diet/alcohol/illness)
EXAMINATION – skin disease/ alcoholic liver disease
Describe the consequences of folate deficiency
Megaloblastic, macrocytic anemia- due to defects in DNA synthesis
Neural tube defects in developing fetus
Increased risk of thrombosis in association with variant enzymes involved in homocysteine metabolism
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)
Summarise neural tube defects
Spina bifida
Anencephaly
ALL PREGNANT WOMEN TAKE FOLIC ACID 0.4MG PRIOR TO CONCEPTION AND FOR FIRST 12 WEEKS
What are the NICE guideline recommendations for women of standard and high risk of neural tube defects
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
What are very high levels of homocysteine associated with
Very high homocysteine levels are associated with
atherosclerosis
premature vascular disease
What are mildly raised levels of homocysteine associated with
Mildly elevated levels of homocysteine are associated with:
cardiovascular disease DEFINITELY
arterial thrombosis PROBABLY
venous thrombosis POSSIBLY
Describe how folate deficiency is combatted in the U.S.A
1998 food and drug administration in the USA
Grains fortified with folic acid (100micrograms/day)
Describe some classic cases of how B12 deficiencies present
Classic 1:
- 40 y old female with tingling in fingers - Hb 10g/dl and MCV 105 - Family history of auto-immune disease - MEASURE VITAMIN B12 and it is low
Patient with an inflamed tongue (glossitis) Premature grey hair falls over when they close their eyes Loss of proprioception = Romberg’s sign
Describe the consequences of B12 deficiency
Neurological problems
Bilateral peripheral neuropathy
Subacute comined degeneration of the cord
Posterior and pyramidal tracts of the spinal cord- can lead to paralysis
Optic atrophy
dementia
Describe a typical history of a patient with B12 deficiency
Paraesthesiae Muscle weakness Difficult walking Visual impairment Psychiatric disturbance
What may be found upon examinations on a patient with B12 deficiency
Examinations:
o Absent reflexes and upgoing plantar responses – combination of UPPER and LOWER motor neuron sign
Describe the different causes of B12 deficiency
POOR ABSORPTION- main cause Reduced dietary intake Stores are large and last for 3-4 years Animal produce Vegans are at risk Infections/infestations Abnormal bacterial flora (stagnant loops) Tropical sprue Fish tapeworm
What is important to remember about B12 absorption
REDUCED ABSORPTION – why??
COMPLEX MECHANISM OF ABSORPTION
CAN GO WRONG IN MANY WAYS
Describe normal B12 absorption
Occurs in small intestine – B12 is then stored – when stores are saturated excess B12 is excreted in the urine
2 methods of absorption
Method 1 - Slow and inefficient (1%)
- duodenum
Method 2..most absorption this way.
B12 must combine with intrinsic factor
Intrinsic factor is made in the stomach
(parietal cells)
B12-IF binds to ileal receptors
What 3 things are needed for B12 absorption
THREE THINGS ARE ESSENTIAL
Intact Stomach
Intrinsic factor
Functioning small intestine
What can lead to a reduction in intrinsic factor
Reduction in intrinsic factor
a) post gastrectomy b) gastric atrophy c) antibodies to intrinsic factor or parietal cells
What is pernicious anaemia
Autoimmune condition associated with SEVERE LACK OF IF
Peak age: 60 years
Family history
Males have a decreased life expectancy
Ca stomach
Summarise anti-bodies in pernicious anaemia
Intrinsic factor antibodies Occasionally found in other conditions Parietal cell antibodies 90% adults with PA 16% normal females over age of 60 Increased in relative of patients with PA
Some trusts test for parietal cell antibodies before going on to test IF antibodies.
What bowel diseases can lead to impaired B12 absorption
Diseases of small bowel (terminal ileum)
a) Crohns b) Coeliac disease c) surgical resection
Describe some infections which can impair B12 absorption
H Pylori
Giardia
Fish tapeworm
Bacterial overgrowth
Describe some drugs associated with impaired B12 absorption
Metformin
Proton pump inhibitors e.g. omeprazole
Oral contraceptive pill
What investigations can we perform to establish the cause of B12 deficiency
Antibodies to parietal cells and intrinsic factor
Anitbodies for coeliac disease
Breath test for bacterial overgrowth
Stool for H Pylori
Test for Giardia
OLDEN DAYS - Shilling test (part I and part II)
Describe the Shilling test
§ PART 1 – give injections of B12 to saturate stores and then patient drinks radiolabelled B12 and then they measure excretion of B12 in the urine.
· You would normally expect it to come out in the urine as the stores are full.
· If none is in the urine, there are several possibilities:
o Not absorbing B12 – pernicious anaemia, small bowel disease.
o Hasn’t corrected B12 deficiency before the test.
§ PART 2 – repeat test but with addition of IF and measure excretion of B12 in the urine.
§ Results:
· P1: Low, P2: Normal – pernicious anaemia with autoantibodies to the B12.
If both are low then not autoimmune
What should be done if a patient has normal B12 but has all the classic features of a B12 deficiency
§ Classic case but with normal B12 – unsettling as could lead to B12 neurological deficits.
o You would treat this as a B12 deficiency (to be safe) but send-off other markers to be assessed from the B12 metabolic pathway.
o Measure; methylmalonyl acid and homocysteine and look for anti-intrinsic factor antibodies.
Describe the treatment for B12 deficiency
Injections of B12…. 1000ug (i.m) 3x/week for 2 weeks Thereafter every 3 months IF NEUROLOGICAL INVOLVMENT B12 injections alternate days until no further improvement – up to 3 weeks Thereafter every 2 months
Neurological symptoms may not be reversible
A 49 y old man with grey hair and blue eyes presents with anaemia. His blood count is as follows:
Hb 90g/l WBC 4 x 109/l platelets 160 x 109/l MCV 110fl
Folate, B12, thyroid function, liver function
As all these test for microcytosis.
What is a consequence of the delayed maturation of nuclei in megaloblastic anaemia
As a result of the delayed maturation of the nuclei, many red cells die in the bone marrow and the activity of red cell production increases to compensate. This is referred to as ineffective erythropoiesis.
What is pernicious anaemia also known as
autoimmune gastric atrophy (“pernicious anaemia”)
Describe dietary intake of B12
Cobalamin (vitamin B12) is a bacterial product that is ingested and stored by animals.
It is found in meat, cheese, salmon, cod, milk, eggs
How much B12 is needed and how much is stored in the liver
1.5-3 mcg/day required
Store: 2-5 mg (will last several years)
What is important to remember between the difference between loss of folate and loss of B12
400-600 mcg
You run out of folate much quicker than B12
What is the role of B12 in the nervous system
Myelination
Describe the passage of B12 in the body
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
Describe the passage of folic acid in the body
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
Name some drugs that can cause malabsorption of folate
Drugs (e.g. colestyramine, sulfasalazine and methotrexate)
What is coeliac disease caused by and how can we diagnose it
Sensitivity to gliadin (group of proteins found in wheat) leads to subtotal villous atrophy with crypt hyperplasia in the duodenum.
Anti-gliadin (transglutaminase) antibodies
Duodenal biopsy
Describe some other tests involved in folate deficiency
erum folate – useful as a screening test
· Shows diurnal variation
· Affected by recent changes in diet
Red cell folate – useful as confirmatory test
What would you expect the serum folate and red cell folate to be in a patient with B12 deficiency
Serum folate = high
Red cell folate = LOW
This is because B12 is required for the folate to enter the red blood cells
What is the relationship between Hb levels and neurological symptoms in B12 deficiency
Inverse relationship between Hb level and neurological symptoms
Explain the neurological damage in B12 deficiency
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
Summarise the symtpoms of B12 deficiency
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
Describe some tests for B12 deficiency
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.
Describe some newer tests for B12 deficiency
Plasma homocysteine (high in B12 and folate deficiency) Serum methyl malonic acid levels Holotranscobalamin levels (transcobalamin II)
How are folate or B12 deficiencies treated
Oral folate or oral cyanobalamin for dietary deficiency or increased demand
Parenteral (IM/SC) hydroxycobalamin for malabsorption due to pernicious anaemia or bowel disease
