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C - Porphyrias (E) Flashcards

(59 cards)

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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

Study These Flashcards
A

congenital erythropoietic porphyria
porphyria cutanea tarda
erythropoietic protoporphyria

25
enzyme affected in acute intermittent porphyria
HMB synthase
26
enzyme affected in ALA dehydratase deficiency (PBG synthase deficiency)
PBG synthase
27
enzyme affected in hereditary coproporphyria
coproporphyrinogen oxidase
28
enzyme affected in variegate porphyria
protoporphyrinogen oxidase
29
enzyme affected in congential erythropoieitc porphyria
uroporphyrinogen III synthase
30
enzyme affected in porphyria cutanea tarda
uroporphyrinogen decarboxylase
31
enzyme affected in erythropoietic protoporphyria
ferrochetolase
32
most common porphyria
porphyria cutanea tarda (1/25,000)
33
which porphyria will you see in A&E
acute intermittent porphyria (1/100,000)
34
which prophyria is the most common one in kids
erythropoietic protoporphyria (EPP)
35
what does ALA synthase deficiency cause
NOT PORPHYRIA x linked sideroblastic anaemia
36
is ALA dehydratase deficiency common
NO - very rare
37
what builds up in ALA drhydratase deficiiency
ALA but not PBG
38
precipitating factors that cause acute intermittent porphyrias
ALA synthase inducers - barbs, sterods, ethanol, antiuconvulsants stress reduced calroic intake endocrine - premenstrual
39
Dx of AIP
increased urinary PBG PBG gets oxidised so goes from yellow to purple
40
tx of AIP
avoid attacks IV carbs - old Tx IV haem arginate ** key Tx
41
how does haem arginate work as a Tx for AIP
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
which porphyrias are both acute and cutaneous
hereditary coproporphyria variegate porphyria
43
why do you get neurovisceral Sx in hereditary coproporphyria and variegate porphyria
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
inheritance pattern of HCP
AD
45
Sx of HCP
acute neurovisceral attack skin lesions / fragility - inc blisters, esp on back of hands
46
Sx of VP
skin lesions - blistering, on back of hands neurovisceral Sx too
47
how can you differentiate between the acute porphyrias
AIP - no skin lesions HCP and VP - skin lesions urinary / faecal porphyrins - high in HCP/VP not AIP
48
best Ix for acute porphyrias
urine sample, protected from light
49
how do non acute porphyrias present
skin sx following sun exposure (hrs - days)
50
which non acute porphyria is non blistering
EPP - erythropoietic protoporphyria
51
EPP Sx
photosensitivity burning itching oedema --> all following sun exposure
52
what can cause acquired PCT
liver disease and drugs
53
how is EPP Ix and why
RBC protoporphyrin (blood test) --> not a urine test as not detected there
54
what are EPP and CEP associated with
myelodysplastic syndromes
55
if acute features (neurovisceral) of ?porphyria, what Ix should you do
urine PBG (protected from light)
56
is the urine PBG is raised, what needs to be done next
enzyme activity urine / faecal porphyrins DNA
57
if skin features are present in ?porphyria, what Ix should you do
plasma / urine / faecal porphyrins
58
if the patient presents with photosensitivity in ?porphyria, what Ix should you do
red cell protoporphyrins
59
22F on holiday, drinking heavily. Presents to A&E Abdo pain, nausea, vomitting, paranoia, tonic/clonic seizures, blurred vision and flashing lights. DDx?
porphyria - AIP preg

Pathology (87 decks)

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