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6th February 2024
Porphyria and Metalloproteins
As we have already mentioned, haemoglobin is a vital metalloprotein. Therefore, disorders relating to the synthesis of this protein can lead to clinical abnormalities. One prominent group of such disorders are termed porphyria. These are a group of inherited disorders of haem synthesis resulting in the accumulation of porphyrin and its precursors.
Depending on which enzyme involved in haem synthesis is deficient, there are seven main types of porphyria. This range of possible aetiologies leads to many clinical and biochemical features. The full list comprises
| Porphyria | Enzyme | Inheritance Pattern |
|---|---|---|
| Aminolaevulinic acid dehydratase porphyria (ADP) | Aminolaevulinic acid dehydratase | Autosomal recessive |
| Acute intermittent porphyria (AIP) | Porphobilinogen deaminase | Autosomal dominant |
| Congenital erythropoietic porphyria (CEP) | Uroporphyrinogen III synthase | Autosomal recessive |
| Porphyria cutanea tarda (PCT) | Uroporphyrinogen decarboxylase | Usually, autosomal dominant |
| Hereditary coproporphyria (HCP) | Coproporphyrinogen oxidase | Autosomal dominant |
| Variegate porphyria (VP) | Protoporphyrinogen oxidase | Autosomal dominant |
| Erythropoietic protoporphyria (EPP) | Ferrochelatase | Autosomal dominant |
There are numerous ways of classifying porphyria – most commonly by their clinical features:
- Acute porphyria featuring neuropsychiatric features: ADP and AIP.
- Cutaneous porphyria primarily affects the skin: PCT, EPP, and CEP.
- Mixed porphyria with features of both: VP and HCP.
However, we will focus on the three most clinically relevant porphyria: AIP, VP, and PCT.
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