RT Book, Section A1 Desnick, Robert J. A1 Balwani, Manisha A2 Jameson, J. Larry A2 Fauci, Anthony S. A2 Kasper, Dennis L. A2 Hauser, Stephen L. A2 Longo, Dan L. A2 Loscalzo, Joseph SR Print(0) ID 1160017885 T1 The Porphyrias T2 Harrison's Principles of Internal Medicine, 20e YR 2018 FD 2018 PB McGraw-Hill Education PP New York, NY SN 9781259644016 LK accesspharmacy.mhmedical.com/content.aspx?aid=1160017885 RD 2024/03/28 AB The porphyrias are metabolic disorders, each resulting from the deficiency or increased activity of a specific enzyme in the heme biosynthetic pathway (Fig. 409-1 and Table 409-1). These enzyme disorders are inherited as autosomal dominant, autosomal recessive, or X-linked traits, with the exception of porphyria cutanea tarda (PCT), which is usually sporadic (Table 409-1). The porphyrias are classified as either hepatic or erythropoietic, depending on the primary site of overproduction and accumulation of their respective porphyrin precursors or porphyrins (Tables 409-1 and 409-2), although some have overlapping features. For example, PCT, the most common porphyria, is hepatic and presents with blistering cutaneous photosensitivity, which is typically characteristic of the erythropoietic porphyrias (EPPs).