Porphyrins, Porphobilinogen, and δ-Aminolevulinic Acid

Porphyrias are disorders arising from inherited or acquired enzymatic defects in the heme biosynthetic pathway. Currently eight porphyria disorders are described which are often grouped into acute hepatic porphyrias and cutaneous porphyrias. As a group, genetic porphyrias demonstrate various modes of inheritance including autosomal dominant, autosomal recessive, and X-linked transmission. Some porphyrias exhibit reduced penetrance demonstrating the importance of modifier genes and environmental influences on clinical expressivity. Conversely, most individuals with porphyria cutanea tarda have an acquired enzyme deficiency which can be induced by similar environmental and genetic factors. These complexities combined with the expanding availability of treatments highlight the importance of biochemical testing for this pathway.