Etimologia
- Porphyros = purple (grego)
- → cor purpúrica/avermelhada da urina e fezes nas profirias devido à acumulação de precursores
Mechanism
- Porphyrins have cyclic ring (anel aromático) structure
- → can aborb energy radiation of a specific wavelength (400-410nm - Soret band)
- Soret band is 400-410nm (low UVA and high visible - blue)
- Can penetrate window glasses
- Need physical blocking sunscreens (specially those containing iron oxide)
- “Usual” UVA and UVB sunscreens will not block this!!!
- Porphirins may be hidrophilic or lipophilic
- Hidrophilic have more carboxyl groups
- Lipophilic → not present in urine, liver deposition → gallstones and pancreatitis
- Determines accumulation in different structures and membrane permeability
Study approach
- Memorize the pathway
- Memorize where watch disease occurs
- Use the pathway to figure out what will be elevated in each disease
Pathway
Classification
- According to clinical presentation
- Acute Porphyrias (mutação antes da formação do anel aromático Hidroximetilbilano)
- Acute Intermittent porphyria - Porphobilinogen deaminase
- ALA deshydratase deficiency porphyria
- Mucocutaneous involvement (mutação depois da formação do anel aromático Hidroximetilbilano)
- Note that: acute intermittent porphyria does not have cutaneous findings and is not included here
- Porphyria cutanea tarda (PCT) - Uroporphyrinogen decarboxylase
- Erythropoietic protoporphyria (EPP) - Ferrochelatase
- Congenital erythropoietic porphyria (CEP) - Uroporphyrinogen III synthase
- Hepatoerythropoietic porphyria (HEP) - Uroporphyronogen decarboxilase
- Autossomal recessive, but much more severe that PCT
- Mixed: acute attacks PLUS cutaneous involvement
- Variegate porphyria (VP)- Protoporphyrinogen oxidase
- Hereditary coproporphyria - Coproporphyrinogen oxidase (CPO)
- “Atypical” porphyrias
- Pseudoporphyria (drug or hemodyalisis) - No abnormal elevation of porphyrins
- According to site of abnormality
- Hepatic
- Acute intermittent porphyria
- Porphyria variegada Porphyria Cutanea Tarda (PCT)
- Hereditary coproporphyria
- Erythropoietic
- Congenital erythropoietic porphyria
- Erythropoietic Protoporphyria (EPP)
Tips
- CEP - “colorless” (anemia), erythrodontia, photosensitive (hence “CEP” like the name)
- PCT - urine turns pink at 365nm
- VP - urine turns pink at 626nm; VP - PPO
- EPP - E&F for ferrochelatase, not water soluble → liver deposition → gallstones and pancreatitis; most common childhood porphyria
- CEP, HEP and EPP are autosomal recessive, others are dominant
- Disorders/medications that stress liver function → increased risk of PCT
- HCV, alcohol, hemochromatosis, estrogen
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