By Disease Name > Porphyrias

Porphyrias

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•porphyrins are readily excitable by light with a wavelength of about 400nm; most patients have an action spectra that is maximal at 400nm with a lesser response at 500-600nm
•photosensitivity of the skin is seen in all porphyrias except: the acute intermittent form
•most of the porphyrins are inherited in an autosomal dominant form except: congenital erythropoietic porphyria

 

 

ALA synthase:

•the starting point for heme biosyntheses is the formation of d-aminolaevulinic acid (ALA) from glycine and succinyl CoA
•the rate limiting enzyme of the pathway for heme biosynthesis (in both the liver and the erythroid cell)
•is under negative feedback control from heme

 

 

histology (of all cutaneous porphyrias):

•varying amounts of PAS (+) and diastase (-) material around papillary dermal vessels
•this material represents duplicated basement membrane material and stains with antibodies to type IV collagen
•DIF reveals immunoglobulin and occasionally complement deposition in this material (thought to be due to trapping rather than an immunologic reaction)

 

VP, AIP, HCP

•all three autosomal dominant
•acute attacks – all three:
•GI – colicky abdominal pain,  N/V
•CNS – peripheral neuropathy with pain;  weakness;  paralysis;  delirium;  seizures
•skin – involved in HCP (30%) and VP;  identical changes to PCT

 

mneomonic:  VP is the Vice President and the others are his HAPless underlings

•VP = skin changes and acute attacks
•Heriditary Coproporphyria = identical clinically to VP, but different enzyme
•AIP = VP minus the skin changes
•PCT = VP minus the acute attacks

 

(highest incidence of VP is in South Africa)        

 

disease:        deficient enzyme:

 

PCT        uroporphyrinogen decarboxylase

 

EPP        ferrochelatase

 

VP        protoporphyrinogen oxidase

 

AIP        porphobilinogen deamniase (PBGD)

 

Hereditary Coproporphyria        coproporphyrinogen oxidase