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Pathology > C - Porphyrias (E) > Flashcards

C - Porphyrias (E) Flashcards

1
Q

define porphyrias

A

deficiencies in enzymes of the haem biosynthestic pathway, leading to overproduction of toxic haem precursors

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2
Q

sx of porphyrias

A

acute neuro - visceral attacks
cutaenous - blistering or non blistering

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3
Q

what is the structure of haem

A

fe2+ in centre
4 pyrrolic rings around iron

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4
Q

what is cytochrome

A

electron transport chain component in mitochondria

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5
Q

which cells does haem synthesis affect

A

erythroid and liver cells

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6
Q

describe 1st step of haem biosynthesis and where it occurs

A

succinyl coA + glycine –> 5 ALA (ALA synthase)
mitchondria

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7
Q

what are the steps of haem biosynthesis that happen outside of mitochondria

A

ALA –> PBG (PBG synthase)
PBG –> HMB (HMB synthase)
HMB –> uroporphyrinogen I or III
uroporphyrinogen III –> coproporphyrinogen III

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8
Q

what is PBG

A

porphobilinogen

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9
Q

what is HMB

A

hydroxymethylbilane

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10
Q

what is HMB converted into

A

uroporphyrinogen I or II

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11
Q

how is it determined whether uroporphyrinogen I or II is made

A

I needs an ezyme, so if the enzyme isn’t present then II is made

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12
Q

what enzyme converts HMB to uroporphyrinogen III

A

uropoprphyrinogen III synthase

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13
Q

what are the 2 final steps of haem synthesis that take place in the mitochondria

A

coproporphyrinogen –> protoporphyrinogen IX –> protoporphyrin IX –> haem

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14
Q

what enzyme converts proptoporphyrin IX to haem

A

ferrochetalase

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15
Q

what enzyme converts coproporphyrinogen to protoporphyrinogen IX

A

coproporphyrinogen oxidase

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16
Q

what enzyme converts protoporphyrinogen IX to protoporphyrin IX

A

protoporphyrinogen oxidase

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17
Q

how can porphyrias be classified

A

erythroid / hepatic
acute / non acute
neurovisceral / skin lesions

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18
Q

what causes neurovisceral Sx

A

5 ALA build up - neurotoxic

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19
Q

what causes the skin lesions

A

activated porphyrins and O2

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20
Q

what are porphyrinogens

A

precurosor to porphyrins

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21
Q

how are porphyrinogens different to porphyrins

A

porphyrinogens are colourless and porphyrins are coloured

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22
Q

contrast stability of porphyrins vs porphyrinogens

A

porphyrinogens are unstable - readily oxidised
porphyrins are varied - near the start of pathway are stable, later on are not

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23
Q

which porphyrias are acute

A

ALA dehydratase
acute intermittent porphyria
hereditary coproporhyria
variegate porphyria

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24
Q

which porphyrias are non acute

A

congenital erythropoietic porphyria
porphyria cutanea tarda
erythropoietic protoporphyria

25
Q

enzyme affected in acute intermittent porphyria

A

HMB synthase

26
Q

enzyme affected in ALA dehydratase deficiency (PBG synthase deficiency)

A

PBG synthase

27
Q

enzyme affected in hereditary coproporphyria

A

coproporphyrinogen oxidase

28
Q

enzyme affected in variegate porphyria

A

protoporphyrinogen oxidase

29
Q

enzyme affected in congential erythropoieitc porphyria

A

uroporphyrinogen III synthase

30
Q

enzyme affected in porphyria cutanea tarda

A

uroporphyrinogen decarboxylase

31
Q

enzyme affected in erythropoietic protoporphyria

A

ferrochetolase

32
Q

most common porphyria

A

porphyria cutanea tarda (1/25,000)

33
Q

which porphyria will you see in A&E

A

acute intermittent porphyria (1/100,000)

34
Q

which prophyria is the most common one in kids

A

erythropoietic protoporphyria (EPP)

35
Q

what does ALA synthase deficiency cause

A

NOT PORPHYRIA
x linked sideroblastic anaemia

36
Q

is ALA dehydratase deficiency common

A

NO - very rare

37
Q

what builds up in ALA drhydratase deficiiency

A

ALA but not PBG

38
Q

precipitating factors that cause acute intermittent porphyrias

A

ALA synthase inducers - barbs, sterods, ethanol, antiuconvulsants
stress
reduced calroic intake
endocrine - premenstrual

39
Q

Dx of AIP

A

increased urinary PBG
PBG gets oxidised so goes from yellow to purple

40
Q

tx of AIP

A

avoid attacks
IV carbs - old Tx
IV haem arginate ** key Tx

41
Q

how does haem arginate work as a Tx for AIP

A

porphyrias are part of haem synthesis pathway, so if you flood body w haem, the pathway gets turned off so toxic precursors not made

42
Q

which porphyrias are both acute and cutaneous

A

hereditary coproporphyria
variegate porphyria

43
Q

why do you get neurovisceral Sx in hereditary coproporphyria and variegate porphyria

A

the eynzymes that are affected inhibit HMB synthase which causes backing up so increase in PBG and increase in ALA –> ALA is neurotoxic so causes Sx

44
Q

inheritance pattern of HCP

A

AD

45
Q

Sx of HCP

A

acute neurovisceral attack
skin lesions / fragility - inc blisters, esp on back of hands

46
Q

Sx of VP

A

skin lesions - blistering, on back of hands
neurovisceral Sx too

47
Q

how can you differentiate between the acute porphyrias

A

AIP - no skin lesions
HCP and VP - skin lesions
urinary / faecal porphyrins - high in HCP/VP not AIP

48
Q

best Ix for acute porphyrias

A

urine sample, protected from light

49
Q

how do non acute porphyrias present

A

skin sx following sun exposure (hrs - days)

50
Q

which non acute porphyria is non blistering

A

EPP - erythropoietic protoporphyria

51
Q

EPP Sx

A

photosensitivity
burning
itching
oedema
–> all following sun exposure

52
Q

what can cause acquired PCT

A

liver disease and drugs

53
Q

how is EPP Ix and why

A

RBC protoporphyrin (blood test)
–> not a urine test as not detected there

54
Q

what are EPP and CEP associated with

A

myelodysplastic syndromes

55
Q

if acute features (neurovisceral) of ?porphyria, what Ix should you do

A

urine PBG (protected from light)

56
Q

is the urine PBG is raised, what needs to be done next

A

enzyme activity
urine / faecal porphyrins
DNA

57
Q

if skin features are present in ?porphyria, what Ix should you do

A

plasma / urine / faecal porphyrins

58
Q

if the patient presents with photosensitivity in ?porphyria, what Ix should you do

A

red cell protoporphyrins

59
Q

22F on holiday, drinking heavily. Presents to A&E
Abdo pain, nausea, vomitting, paranoia, tonic/clonic seizures, blurred vision and flashing lights. DDx?

A

porphyria - AIP
preg

Pathology (87 decks)

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