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Chem Path > Chem Path: Porphyrias > Flashcards

Chem Path: Porphyrias Flashcards

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1
Q

What is porphyrias?

A

Deficiencies in enzymes of the haem synthesis pathway, leading to an overproduction of haem intermediate toxic products

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2
Q

What are the 2 ways porphyrias can present?

A

Acute neuro-visceral attacks

Cutaneous symptoms

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3
Q

What is haem?

A

Fe core with 4 pyrrolic rings around it with double bonds

Carries oxygen

Good for redox reactions

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4
Q

What is a key difference between haem and its precursors

A

Precursors do not have double bonds between the rings

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5
Q

Which cells does porphyrias affect the most?

A

Erythroid cells and liver cytochromes

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6
Q

Why is cytochrome crucial?

A

It is needed for the electron transport chain in the mitochondria

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7
Q

What starts the haem synthesis pathway in the mitochondria?

A

Succinyl CoA + Glycine = 5 ALA by ALA synthase

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8
Q

What is step 2 in the haem synthesis pathway?

A

5 ALA leaves the mitochondria and is converted to PBG via PBG synthase

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9
Q

What is step 3 in the haem synthesis pathway?

A

PBG is converted to HMB by HMB synthase

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10
Q

What is step 4 in the haem synthesis pathway?

A

HMB is converted to Uroporphyrinogen 3 if Uroporphyrinogen synthase is present. Otherwise it turns into Uroporphyrinogen 1

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11
Q

What is step 5 in the haem synthesis pathway?

A

Uroporhyrinogen 3 is converted to coproporphyrinogen 3

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12
Q

What is step 6 in the haem synthesis pathway?

A

coproporphyrinogen 3 enters the mitochondria and is converted to protoporphyrinogen 9

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13
Q

What is step 7 in the haem synthesis pathway?

A

protoporphyrinogen 9 is converted to protoporhyrin 9

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14
Q

What is step 8 in the haem synthesis pathway?

A

protoporhyrin 9 is converted to Haem by ferrochetalase

If no Fe present at this stage, you get metal free protoporhyrin or zinc protoporhyrin

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15
Q

What are the 2 principle sites of enzyme deficiency?

A

Erythroid

Hepatic

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16
Q

What are the 3 types of presentations

A

Neurovisceral
Blistering cutaneous
Non blistering cutaneous

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17
Q

What gives neurovisceral/acute symptoms?

A

Accumulation of 5 ALA

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18
Q

What gives skin lesions?

A

Accumulation of porphyrinogens, which is oxodised to active porphyrins in UV light

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19
Q

What are porphyrinogens

A

Precursors to porphyrins

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20
Q

What colour are porphyrinogens

A

Colourless

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21
Q

What happens in porphyria

A

porphyrinogens are raised and are usually colourless / yellow. They rapidly oxidise to porphyrins and turn red or purple

22
Q

How are porphyrins excreted?

A

The ones near the start of the pathway are water soluble and are excreted via urine while the ones towards the end of the pathway are less soluble and excreted via faeces

23
Q

What is the most common type of porphyria?

A

porphyria cutenea tarda

24
Q

What most common porphyria in kids?

A

Erythropoietic protoporphyria - blistering porphyria

25
Q

What can cause acute porphyria

A

PBG synthase deficiency

26
Q

What happens in PBG synthase deficiency

A

Accumulation of ALA

27
Q

What does Accumulation of ALA cause

A

Neurovisceral symptoms - coma, bulbar palsy, motor neuropathy
ABDO PAIN
Psychiatric symptoms

28
Q

What causes acute intermittent porphyria (AIP)?

A

HMB synthase deficiency

29
Q

What happens in HMB synthase deficiency

A

Accumulation of ALA and PBG

30
Q

How is HMB synthase deficiency inherited

A

Autosomal dominant

31
Q

What are the symptoms of HMB synthase deficiency

A

Nuerovisceral symptoms due to accumulation of ALA

Abdo pain, vomiting, tachycardia, hypertension, hyponatraemia, seizures, psyco symptoms, sensory loss, muscle weakness, arrythmias, cardiac arrest,

NO CUTANEOUS SYMPTOMS

32
Q

Why are there no cutaneous symptoms in HMB synthase deficiency

A

As there is no production of porphyrinogen

33
Q

What can precipitate HMB synthase deficiency

A

ALA synthase inducers (barbiturates, steroids, ethanol, anti convulsants)
Reduced caloric intake

34
Q

How is HMB synthase deficiency diagnosed

A

Increased urinary PBG and ALA - ensure urine not exposed to light as it will cause PBG to be oxidised to prophobilin
Decreased HMB synthase activity in erythrocytes

35
Q

How to treat HMB synthase deficiency ?

A

Avoid precipitating factors

IV carbohydrate to inhibit ALA synthase

IV haem arginate

36
Q

What are the general symptoms of acute vs chronic porphyrias

A

Acute - Neurovisceral

Chronic - Cutaneous (Skin lesion)

37
Q

What are the 2 acute porphyrias that present with cutaneous symptoms?

A 
Hereditary coproporphyria (HCP) - Due to coproporphyrinogen oxidase deficiency 
Variegate porphyria (VP) - Due to protoporphyrinogen oxidase deficiency
38
Q

Can you get neuro symptoms with HCP and VP and if so why?

A

Yes

As the build up in pre products can inhibit HMG synthase, causing accumulation of PBG and ALA

39
Q

How to diagnose HCP ad VP?

A

Detect porhyrinogens in stool as these molecules are not very soluble

40
Q

How do HCP and VP present?

A

Nuero symptoms - acute

Blistering
On back of hands and neck
Appear after sun exposure

41
Q

How are HCP and VP inherited?

A

Autosomal dominant

42
Q

How do you differentiate between the 3 acute porphyrias (HCP, VP and AIP)?

A

AIP - No cutaneous symptoms
All 3 would have raised urine PBG and porphyrins
AIP will NOT have raised faecal porphyrins
DNA analysis

43
Q

How to non acute porphyrias present?

A

Only cutaneous symptoms

44
Q

What are the 3 enzyme deficiencies in non acute porphyrias and what are they commonly associated with?

A

Uroporphyrinogen III synthase - Congenital erythropoetic porphyria
Uroporphyrinogen decarboxylase - porphyria cutanea tarda (most common porphyria)
Ferrochetalase - Eryhtropoetic protoporphyria (most common in kids)

The first 2 are blistering

45
Q

How does Eryhtropoetic protoporphyria present

A 
NOT blistering
Photosensitivity 
Burning
Itching
Oedema 
All following sun exposure
46
Q

How is Eryhtropoetic protoporphyria detected and treated

A

Measure RBC protoporphyrin concentration
Cannot measure in urine

Sun avoidance is the only treatment

47
Q

What types of PCT are there?

A

3
2 of them are familial
1 is acquired (mostly via liver disease)

48
Q

How does PCT present?

A

Vesicles on sun exposed areas
Crusting
Superficial scarring
Pigmentation

49
Q

What can PCT like syndromes be triggered by?

A

Hexachlorobenzene

50
Q

What are Eryhtropoetic protoporphyria and congenital Eryhtropoetic porphyria usually associated with

A

Myelodysplastic syndromes

51
Q

Summarise the diagnostic approach to porphrias

A

If there are acute features, do urine PBG
If urine PBG raised check urine/faecal porphyrins, enzyme activity and DNA

If skin features present send off urine/faecal/plasma porphyrins

If there is photosensitivity check RBC protoporhyrins

52
Q

Low Na associated with AIP is most likely due to what?

A

SIADH

Chem Path (22 decks)

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