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Chem Path > Porphyrias > Flashcards

Porphyrias Flashcards

1
Q

What is porphyria?

A

Deficiency (partial/complete) of enzymes in haem biosynthesis –>
Overproduction of toxic haem precursors

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2
Q

How do we classify porphyria’s?

A

Principal site of enzyme deficiency
o Erythroid or hepatic

Clinical presentation
o Acute or non-acute
o Neurovisceral or skin lesions

Not perfect, there are overlaps

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3
Q

What are 3 clinical presentations of porphyria’s?

A
  1. Neurovisceral symptoms
  2. Blistering cutaneous symptoms
  3. Non-blistering cutaneous symptoms
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4
Q

What causes neurovisceral symptoms in porphyria’s?

A

Accumulation of 5-ALA which is neurotoxic

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5
Q

What causes cutaneous symptoms in porphyria’s?

A

Porphyrin pre-cursors accumulate in the skin
Pre-cursors are oxidised by UV light
Become toxic

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6
Q

What is the difference between porphyrinogens and porphyrins?

A

Porphyrinogens are pre-cursors to porphyrins

*Porphyrinogens are RAISED in porphyria (colourless and unstable), will oxidise quickly and become coloured

  • Porphyrins are HIGHLY COLOURED (water soluble at start of chain, less soluble at end)
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7
Q

What is the porphyria caused by PBG synthase?

A

ALA Dehydratase / Plumboporphyria

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8
Q

What is the porphyria caused by HMB synthase?

A

Acute intermittent porphria

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9
Q

What enzyme causes hereditary coproporphyria?

A

Coproporphyrinogen oxidase

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10
Q

What enzyme causes variegate porphyria?

A

Protoporphyrionogen oxidase

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11
Q

What are the acute porphyrias?

A

ALA Dehydratase / Plumboporphyria
Acute intermittent porphria
Hereditary Coproporphyria
Variegate porphyria

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12
Q

What are the non-acute porphyrias?

A

Congential erythropoietic porphria
Porphyria cutanea tarda
Erythropoietic protoporphria

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13
Q

What enzyme causes Congential erythropoietic porphria?

A

Uroporphyrinogen III synthase?

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14
Q

What enzyme causes Porphyria cutanea tarda?

A

Uroporphyrinogen decarboxylase

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15
Q

What enzyme causes Erythropoietic protoporphria?

A

Ferrochetolase

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16
Q

What is the most common porhyria?

A

Porphyria cutanea tarda

17
Q

What is the most common porphyria in children?

A

Erythropoietic protoporphyria

18
Q

What is ALA synthase deficiency?

A

NOT at porphyria
X-linked sideroblastic anaemia

19
Q

What happens in Acute Porphyria / Plumboporphyria?

A

Accumulation of ALA
Lack of PBG

19
Q

What are the symptoms of Acute Porphyria / Plumboporphyria?

A

Neurological (e.g. coma, bulbar palsy, motor neuropathy)
Abdominal pain (most important feature)
+/- psychiatric symptoms

20
Q

What happens in Acute Intermittent Porphyria?

A

HMB Synthase Deficiency
PBG goes up
ALA goes up

21
Q

What are the clinical signs for AIP?

A

No cutaneous symptoms
Neurovisceral:
Abdominal pain and vomiting
Tachycardia and hypertension
Constipation, urinary incontinence
Hyponatraemia (SIADH) ± seizures
Psychological symptoms
Sensory loss/muscle weakness
Arrhythmias/cardiac arrest

22
Q

What are precipitating factors for AIP?

A

ALA synthase inducers – barbiturates, steroids, ethanol, anti-convulsants
Stress – infection, surgery
Reduced caloric intake
Endocrine factors – F>M, pre-menstrual

23
Q

How do you diagnose AIP?

A

Urine sample - protect from light and get to lab, will turn purple in light

24
Q

How can someone avoid AIP attacks?

A

adequate nutritional intake, avoid precipitating drugs, prompt tx for infection

25
Q

What is the treatment for AIP?

A

Abundance of Haem will turn pathway off
Therefore give IV Haem Arginate
Also IV carbohydrate

26
Q

Which acute porphyrias have skin lesions?

A

Hereditary Coproporphyria
Variegate Porphyria

27
Q

What are the features of HCP?

A

Autosomal dominant
Acute neurovisceral attacks
Skin lesions – blistering, skin fragility [back of hands, after sun]
Lesions hours-days after sun exposure

28
Q

What are the features of VP?

A

Autosomal dominant
Acute attacks
Skin lesions

29
Q

How can you differentiate between the acute porphyrias?

A

AIP - no lesions
Urine PBG - raised in all
Porphyrins in urine and faeces - HCP and VP
DNA for definitive diagnosis

30
Q

What is important re non-acute porphyrias?

A

Only present with skin lesions (blistering or non-blistering)
No neuro-visceral manifestations

31
Q

What are the non-acute porphyrias?

A

Congenital Erythropoietic Porphyria (CEP)
Porphyria Cutanea Tarda (PCT)
Erythropoietic Protoporphyria (EPP)

32
Q

What are the features of PCT?

A

Acquired (80%), inherited (20%)
Skin symptoms only – vesicles on sun-exposed areas

Biochemistry:
- Urine/plasma uroporphyrins + coproporphyrins are increased
- Ferritin increased

33
Q
A

Chem Path (5 decks)

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