Porphyrias
- a set of genetic (AD,AR and X-linked versions) metabolic disorders, each a defect in one of the 8 enzymes in the heme biosynthetic pathway resulting in the accumulation of precursors of heme. Porphyrins are the major precursors.
- can be classified as hepatic or erythropoietic based on whether the heme precursors 1st accumulate in the liver or the bone marrow and red blood cells
- also classified as acute and chronic or cutaneous porphyrias
“classic triad” suggesting acute porphyria:
- abdominal pain
- central nervous system abnormalities
- peripheral neuropathy
| Hepatic | Erythropoietic | Acute | Chronic |
|---|---|---|---|
| • acute intermittent porphyria (AIP) • variegate porphyria (VP) • aminolevulinic acid dehydratase deficiency porphyria (ALAD) • hereditary coproporphyria (HCP) • porphyria cutanea tarda (PCT) | • Congenital erythropoietic porphyria • Erythropoietic porphyria • Hepatoerythropoietic porphyria • X-linked protoporphyria | • Acute intermittent porphyria • ALA dehydratase deficiency porphyria (Doss porphyria) • Hereditary coproporphyria • Variegate porphyria | • Congenital erythropoietic porphyria • Erythropoietic porphyria • Hepatoerythropoietic porphyria • Porphyria cutanea tarda • X-linked protoporphyria |
Hepatic porphyrias
- presentation:
- generally neurological
- neuropathic abdominal pain is most common presentation.
- seizures, psychosis
- back pain
- acute polyneuropathy.
- Occasionally some cutaneous manifestations.
- Investigations:
- Urine porphobilinogen (PBG)
- Decreased erythrocyte porphobilinogen deaminase (PBGD) activity
- commonly - hyponatraemia and raised transaminases
- Management:
- supportive - IV fluid, analgesia
- IV haem arginate (human hemin) - 3mg/kg (to a maximum of 250mg) once daily for 4 consecutive days.