Heme biosynthesis and the porphyrias

Area of Science:

• Biochemistry
• Genetics
• Metabolic Diseases

Background:

• Porphyrias are a group of genetic metabolic diseases affecting heme biosynthesis.
• Defective enzyme activity in the heme pathway leads to the accumulation of specific intermediates.
• Accumulated intermediates cause either neurological or photosensitive symptoms.

Purpose of the Study:

• To provide an overview of the biochemical steps in heme production.
• To classify porphyrias based on enzyme defects and affected cells (erythroid vs. hepatic).
• To highlight the diagnostic significance of accumulated metabolites.

Main Methods:

• Classification of porphyrias based on the specific enzyme defect in the heme biosynthetic pathway.
• Categorization into erythropoietic or hepatic porphyrias.
• Analysis of accumulated pathway intermediates in plasma, erythrocytes, urine, and feces for diagnosis.

Main Results:

• Eight distinct porphyrias are associated with defects in each of the 8 enzymes of the heme biosynthetic pathway.
• Erythropoietic porphyrias include congenital erythropoietic porphyria (CEP) and erythropoietic protoporphyria (EPP).
• Acute hepatic porphyrias include ALA dehydratase deficiency porphyria, acute intermittent porphyria (AIP), hereditary coproporphyria (HCP), and variegate porphyria (VP).
• Porphyria cutanea tarda (PCT) involves both genetic and environmental factors affecting liver enzyme activity.

Conclusions:

• Distinct patterns of accumulated metabolites are crucial for diagnosing specific porphyrias.
• Understanding the heme biosynthetic pathway is key to comprehending the molecular basis of porphyrias.
• Further research into ALAS2 mutations may reveal new insights into EPP variants.