The porphyrias constitute a family of disorders resulting from deficiencies in the various enzymes of heme biosynthesis which is also called the porphyrin pathway.
The Figure below shows the pathway of heme biosynthesis. Enzyme names are shown in green. Defective enzyme activity leads to the disorders indicated in blue. Click the disease name in the image to go to a descriptive page. Note that the porphyria called hepatoerythropoietic porphyria (HEP) is a disorder caused by defects the gene encoding uroporphyrinogen decarboxylase (UROD) which is the same gene defective in porphyria cutanea tarda (PCT) and thus HEP is discussed in the PCT page.Click here for full-size image