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PathY5 > Porphyria > Flashcards

Porphyria Flashcards

1
Q

What is a prophyria?

A

Deficiencies in enzymes of the haem biosynthetic pathway.

Deficiency of enzymes ranges from partial to complete.

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2
Q

What do porphyrias cause?

A

•Overproduction of toxic haem precursors

–Acute neuro-visceral attacks and/or

–Acute or chronic cutaneous symptoms.

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3
Q

What is Haem?

A
  • Organic heterocyclic compounds
  • Fe2+in centre
  • 4 pyrrolic (tetrapyrrole) rings around the iron
  • Carries oxygen
  • Redox reactions
  • Erythroid cells and liver cytochrome
  • Made in all cells
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4
Q

Draw this out: (x5)

A

:)

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5
Q

Draw out the haem biosynthesis pathway x3

A
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6
Q

What may enzyme deficiencies do?

A

Build-up ALA, PBG or one of the -porphyrinogens

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7
Q

What can porphyrias be classed as?

A

Erythroid or hepatic

Acute or non acute

Neurovisceral or skin lesions

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8
Q

Why do acute/ neurovisceral S/S happen?

A

–5-aminolaevulinic acid is neurotoxic

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9
Q

Why do skin lesions happen?

A

Porphyrinogens

\/ oxidised

Porphyrins

\/ light

Activated porphyrins & O2

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10
Q

What is Porphyrinogens vs. porphyrins?

A

•Porphyrinogens are raised in porphyria

–Colourless compounds

–Unstable and readily oxidised to the corresponding porphyrin by the time urine /faeces reaches lab

•Porphyrins are highly coloured

–Porphyrins near start of the pathway are water soluble – urine (uro-)

–Porphyrins near end less soluble – faeces (copro-)

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11
Q

What are the types of porphyrias?

A
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12
Q

What is ALA synthase deficiency?

A
  • Not a porphyria
  • X-linked sideroblastic anaemia
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13
Q

What is PBG synthase deficiency?

A
  • ‘ALA Dehydratase or Plumboporphyria’
  • Extremely rare form of porphyria
  • Build-up of ALA, but not PBG
  • Diagnostic implications
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14
Q

What are the symptoms of HMB synthase deficiency?

A

Acute Intermittent Porphyria: Autosomal dominant

Neurovisceral attacks!

GI: Abdo pain, vomiting, constipation

Cardiovascular: Tachycardia, Hypertension, arrhythmias, cardiac arrest

Neurological: Seizures (hyponatraemia), sensory loss, weakness, psych symptoms

NO SKIN INVOLVEMENT BECAUSE NO PORPHYRINOGENS MADE!

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15
Q

What may cause symptomatic ‘attacks’ of acute intermittent porphyria?

A

Enzyme activity usually 50% of normal so 90% have no symptoms at all

Precipitating factors for attacks:

ALA synthase inducers: Barbiturates, steroids, ethanol, anticonvulsants

Stress: Infection, surgery

Reduced caloric intake

Endocrine factors: More common in women and premenstrual

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16
Q

How do you diagnose porphyria?

A
  • Increased urinary PBG (and ALA)
  • PBG gets oxidised to porphobilin
  • Decreased HMBS activity in erythrocytes
17
Q

How do you treat porphyria?

A

Conservative: Avoid attacks, Adequate nutritional intake, Avoid precipitant drugs, Prompt treatment infection/illness

Medical: iv carbohydrate, iv haem arginate

18
Q

What are the •Acute porphyrias with skin lesions?

A

Hereditary coproporphyria

Variegate porphyria

19
Q

What does Coproporphyrinogen oxidase cause?

A

•Hereditary Coproporphyria (HCP)

–Autodomal dominant

–Acute neurovisceral attack

–Skin lesions

  • Blistering
  • Skin fragility
20
Q

What is Variegate Porphyria (VP)?

A

•Variegate Porphyria (VP)

–Autosomal dominant

–Acute attacks

–Skin lesions

21
Q

How can we differentiate the acute porhyrias?

A
  • AIP – no skin lesions
  • HCP & VP – skin lesions
  • Urine PBG – raised in all three
  • Urine and faeces for porphyrins

–Raised HCP or VP, but not AIP

  • Enzyme activity variable
  • DNA definitive but large number of mutations
22
Q

What are Non-Acute porphyrias?

A
  • Only present with skin lesions
  • No neuro-visceral manifestations
23
Q

What are the types of non acute porphyrias?

A
  • Congenital Erythopoietic porphyria
  • Porphyria Cutanea Tarda
  • Erythropoietic protoporphyria
  • Skin affected only e.g. blisters, fagility, pigmentation, erosions etc. delay following sun exposure
  • EPP: photosensitivity, burning, itching oedema following sun exposure
24
Q

What is PCT?

A
  • Inherited or acquired
  • Uroporphyrinogen decarboxylase deficiency
  • Formation of vesicles on sun-exposed areas of skin crusting, superficial scarring, pigmentation

Biochemistry:

  • Urinary (& plasma) uroporphyrins & coproporphyrins increased
  • Ferritin often increased
  • Avoid precipitants (alcohol, hepatic compromise)
25
Q

What is EPP?

A

Photosensitivity only, no blisters

Only erythroid cells affected, therefore need to measure RBC protoporphyrin

26
Q

What are acquired porphyrias?

A

•PCT most cases sporadic without family history

–Formation of specific inhibitor of uroporphyrinogen decarboxylase

  • PCT-like syndrome hexachlorobenzene
  • EPP and CEP a/w myelodysplastic syndromes
27
Q

What is the diagnostic approach to porphyrias?

A
28
Q

Q1: During acute porphyria, the most useful sample to send is…?

  1. Blood
  2. CSF
  3. Urine
  4. Muscle biopsy
  5. Stool
  6. Skin biopsy
A

Urine

29
Q

Q2 Cutaneous erythema without blisters or bullae, most likely indicates…?

A

EPP

30
Q

Q3: Hyponatraemia associated with AIP is due to….

A

SIADH

31
Q

Q4 Urine samples taken during an acute attack for diagnosis should be…

  1. Taken in an acidified container
  2. Protected from light
  3. Alkalinised
  4. Interpreted with a paired serum sample
A

Protected from light

32
Q
A

PathY5 (98 decks)

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