Chemical Pathology 7 - Porphyrias Flashcards
What is haem?
Tetrapyrole rings surrounding a central iron
Roughly summarise the pathway of haem production
ALA + ALA –> PBG
PBG –> HMB
HMB –> EITHER uroporphyriogen 1 or 3
Uroporphyrinogen 3 –> haem
By what 2 factors are porphyrias classified?
Acute/ non-acute
Neurovisceral or cutaneous
What is the cause of cutaneous symptoms in some porphyrias?
Porphyrin precursors build up under the skin and react with UV
Which toxic product leads to neurovisceral symptoms in porphyria?
5-ALA
What is the most common porphyria?
Porphyria cutanea tarda
What is the most common porphyria in children?
Erythropoietic protoporphyria
What are the symptoms of ALA synthase deficiency?
Weirdly, doesn’t cause porphyria!
Instead, causes an X-linked sideroblastic anaemia
What are the 2 types of acute neurovisceral porphyria, which enzyme deficiency causes each, and how can they be clinically differentiated?
Acute intermittent porphyria (most common) = HMB synthase deficiency - causes ATTACKS
ALA dehydratase porphyria = PBG synthase deficiency - more one acute episode than numerous attacks
What are the symptoms of the acute neurovisceral porphyrias?
Motor neuropathy
Psychiatric symptoms
Severe abdominal pain
What is the most likely cause of an acute intermittent porphyria ‘attack’?
Drug that is CYP450 inducer
How can acute porphyria be diagnosed?
Urine left in light changes colour
How should acute intermittent porphyria be managed?
Avoid attacks (adequate nutrition, precipitant drugs, prompt treatment)
IV carbs OR
IV haem arginate
Recall 2 forms of porphyria that have acute neurovisceral AND cutaneous symptoms
Hereditary coproporphyria
Variegate porphyria
How do the cutaneous effects of porphyrias usually present and why?
Blistering on back of hands (most exposed to UV)
