Chemical Pathology

Question 1

Describe the pathogenesis of Pyphoria.

Answer 1

Porphyrigens are self-oxidizing and form porphyrins that react with UV light, leading to oxygen radicals in the skin, blisters, scars, and hypertrichosis
An increase in PBG and dALA mimics neurotransmitters and leads to CNS dysfunction.

Question 2

How does fasting lead to acute porphyric attacks?

Answer 2

An increase in FA oxidation requires upregulation of PGC-1. PGC-1 leads to the build-up of the haem precursor dALA, which causes the acute attack.

Question 3

List factors that may cause an acute porphyrin attack.

Answer 3

Puberty- sex hormones
Fasting
inducing of cytochrome p450

Question 4

What are the signs/symptoms of an APA?

Answer 4

Abdominal pain- acute similar to surgical pain
Sen and motor neuropathy- weakness, bulbar palsy, resp paralysis
Autonomic Neuropathy- Tachycardia, Hypertension, Tachyarrythmia
anxiety, convulsions, psychosis
Hypo Na+

Question 5

How do you manage APA?

Answer 5

Measure PBG and dALA
do not operate
Increase glucose
slowly correct Na+
ICU-ventilator
Haematologist- Haem increase, decrease haemoxgenase.

Question 6

Describe Pyphoria Variegata.

Answer 6

AD
Afrikaans population
R59W single mutation of PPOX
Decrease PPOX
1/300

Question 7

What are the tests for PV?

Answer 7

Protoporphyrin > Coprophyrin in stool
Plasma Fluorescence screening of protein-bound Protoporphyrin

Question 8

Why can PV lead to an acute porphyrin attack?

Answer 8

A decrease in PPOX, leads to an increase in the protoporphyrinogen, and as a result, there is an inhibition of PBG deaminase and as a result an increase in precursors PBG and dALA

Question 9

How do you diagnose PV?

Answer 9

Mutation analysis and Fluorescence screening.

Question 10

How do you treat PV?

Answer 10

Treat acute attack if present
Provide sunscreen.

Question 11

How do you diagnose APA?

Answer 11

Test for PBG and dALA in urine.

Question 12

Why is PPOX required, if Protoporphyrinogen can spontaneously oxidise to protoporphyrin?

Answer 12

The process takes place in the mitochondria, a highly reduced environment.

Question 13

What is the role of folate?

Answer 13

It carries a 1-carbon/methyl fragment required for
synthesis of purines and pyrimidine required for DNA synthesis. Furthermore, it is required for the methylation of homocysteine to form methionine.

Question 14

What is the function of Vit B12?

Answer 14

It is a co-factor for Methionine synthases and Methylmalonyl-mutase.

Question 15

Describe the relationship between folate and Vit B 12.

Answer 15

folate is required for the conversion of homocysteine to methionine of which Vit B12 is also required.

Question 16

What causes a folate deficiency?

Answer 16

Caused by:
poor dietary intake, Lack of leafy greens or folate supplements.
Malabsorption.
Anti-folate chemotherapeutics-methotrexate.

Question 17

What happens in a folate deficiency?

Answer 17

It plays an essential role in DNA/RNA synthesis, hence rapidly dividing cells are affected first.
Mucosal cells- malabsorption
Neural tube defects in Foetus
Anaemia- Megaloblastic, this is because the body favours the SAM process over the DNA/RNA process, thus protecting the nervous system. As a result, insufficient RNA and DNA are synthesized, hence cell division stops and forms megaloblastic RBC.

Question 18

Who gets B12 defiecient?

Answer 18

Poor dietary intake – elderly (tea and toast), alcoholics, and strict vegans who do not take vitamin supplements for years.
People who are unable to release B12 from proteins – achlorhydria: atrophic gastritis, gastrectomy, long-term PPi’s (omeprazole)
No production of Intrinsic factor: Pernicious anaemia (autoimmune disease against the parietal cell or intrinsic factor)
Damage to the distal Ileum; : Crohn’s disease, gut resections, celiac disease
Theft in the GIT: tapeworms, bacterial overgrowth (blind loops)
Rare congenital deficiencies of transcobalamin II or enzymes that activate B12 intracellularly
B12 deficiency generally takes years to develop and early symptoms are very non-specific. This is why GPs give B12 injections to many patients, – just in case

Question 19

What happens in a Vit B12 Deficiency?

Answer 19

With B12 deficiency the same thing happens – all available folate gets trapped as 5-methyl-THF and this is how B12 deficiency indirectly causes megaloblastic anemia. The problem however is that SAM production also decreases resulting in neurological damage

Question 20

Why would someone with Vit B12 Deficiency seem to have low Folate?

Answer 20

B12 reaction is prioritised, folate essentially becomes trapped as methyl THF, causing ‘functional’ folate deficiency – this is why B12 deficiency also causes megaloblastic
Anaemia – even if the patient is not folate deficient

Question 21

Why is it not advised to give folate in a Vit b12 deficiency?

Answer 21

Both folate and vitamin B12 can cause megaloblastic anaemia. If your patient has B12 deficiency and you only give them folate YOU WILL WORSEN THE NEUROLOGICAL damage!

WHY – giving extra folate allows DNA/RNA synthesis and cell division in all body cells to resume. These growing cells are going to use up any available methionine and SAM (which is already in short supply) to make proteins and in other methylation reactions. Methionine gets “stolen” or diverted from the CNS and with even less SAM in the CNS myelin synthesis deteriorates even further.

Question 22

What are the biochemical Test of folate and Vit B 12 deficiency?

Answer 22

B12- homocysteine and urinary methyl-malonic acid (earliest)
Megaloblastic anaemia and increased LDH 1 isoenzyme late.

Question 23

How to tell if a patient is haemolysing intravascularly?

Answer 23

Unconjugated bilirubin goes up
Elevated urobilinogen on urine dipstix (increase flux through bili pathway)
Red cell enzymes go up in plasma – LDH 1 and AST
Free haemoglobin in plasma is rapidly bound by haptoglobin and cleared so haptoglobin levels go down
Red cell fragments – schistocytes visible on a peripheral blood smear
Haemoglobinuria – in really severe cases

Question 24

How is Iron lost in the body?

Answer 24

GIT cells into the stool, desquamation
blood loss (menstruation)- most common

Question 25

Why is iron important in haem?

Answer 25

Haem is an oxygen carrier and due to irons redox potential it readily binds to gasses such as O2.

Question 26

What happens to iron once it binds to Transferrin?

Answer 26

It becomes soluble and losses its reactivity.

Question 27

Explain how hepcidin controls Iron levels.

Answer 27

Hepcidin binds directly to ferroportin on cells (including epithelial cells, macrophages, etc), causing
internalisation and proteosomal degradation of these transporters, and therefore preventing release of
iron into the circulation.

Question 28

Explain the mechanism for anaemia in chronic disease.

Answer 28

This sequestration is caused by the stimulation
of hepcidin secretion by IL-6 (a cytokine released during inflammation). Hepcidin then prevents the release of iron from the RES as well as from epithelial cells, causing a functional iron deficiency.
Anaemia of chronic disorders is characterised by inadequate erythropoietin production, inhibition of erythroid proliferation, and sequestration of iron into the RES

Question 29

Which biomedical tests are used to differentiate between a functional and a real iron deficiency?

Answer 29

Chr (utilisation of iron in reticulocytes), sTfR, and Ferritin with the calculation of an sTfR/log Ferritin ratio.
C-reactive protein indicates inflammation, and if Ferritin (a positive marker of inflammation) is low real iron deficiency.

Question 30

Besides iron overload, what are other factors that cause an increase in ferritin levels?

Answer 30

usually due to acute or chronic inflammation, chronic alcohol consumption, liver disease, renal failure, metabolic syndrome, or malignancy.
A normal serum transferrin saturation usually excludes iron overload

Question 31

Describe primary iron overload, Haemochromatosis type 1.

Answer 31

mono-allelic genetic disease in Caucasians
homozygous for the C282Y mutation in the HFE protein (High Fe gene)
Mutations in the HFE gene prevent the intracellular signaling required for hepcidin synthesis in the liver. As a result, ferroportin is not degraded and iron can therefore be freely taken up from the GIT and also freely released from macrophages (in the RES) into the circulation.

Question 32

Describe “African iron overload”.

Answer 32

Increased iron absorption from diet is associated with higher iron in diet
beer brewed in iron drums
Ferroportin gene

Question 33

What are the common causes of haemolysis in people with a G6PD deficiency?

Answer 33

Drugs (anti-malarial and sulphur)
DKA
Sepsis
Fava Beans

Question 34

Explain the mechanism of haemolysis in a G6PD patient.

Answer 34

Low G6PD, Low NADPH
Low reduced glutathione
G6PD only way for RBC to get NADPH
RBCs are susceptible to damage caused by free radicals
Build-up causes the cell membrane to become unstable (haemolysis)
Free Radicals then directly destroy Hb
Damage proteins precipitate inside cell, Heinz Bodies.

Question 35

How do RBCs appear in Iron deficiency?

Answer 35

Hypochromic, microcytic
low MCV and MCHC

Question 36

What is the mechanism of action for iron deficiency in a patient with Anaemia of chronic disease?

Answer 36

Chronic inflammation
increase in inflammatory cytokines
cytokines impair the proliferation of erythroid progenitor cells and blunt the erythropoietin response
increased uptake and retention of iron within cells of the reticuloendothelial system
cytokines up-regulate the expression of the divalent metal transporter-1
also inhibits ferroportin
limitation of the availability of iron for erythroid progenitor cells
constant inhibition of ferroportin results in a decrease in iron absorption and eventual iron deficiency.

Question 37

Why is iron toxic when taken in an overdose?

Answer 37

Local GI injury
– iron is extremely corrosive to the GI tract
– manifests as haematemesis and diarrhea
– an erosion of the GI tract allows the absorption of excessive quantities of ingested iron which results in systemic iron toxicity.
Systemic effects
– damage to tissues occurs from iron mediated oxygen free radical generation.
– overdose causes impaired oxidative phosphorylation and mitochondrial dysfunction, which can result in cellular death.
– the liver is one of the organs most affected by iron toxicity, but other organs such as the heart, kidneys, lungs, and the haematologic systems also may be impaired.

Question 38

How do we screen for PBG? Explain the process.

Answer 38

Watson Swhartz test
Urine + Ehrlich solution + sodium acetate
Pink/red Positive: Uro or PBG
Add butanol and Chloroform
chloroform above aqueous solution means positive for PBG