Porphyrias: Pathophysiology and clinical management recommendations for hepatologists

In humans, an enzyme dysfunction in heme biosynthesis results in a heterogenous group of diseases collectively known as porphyrias. From a clinical standpoint, porphyrias can be classified as erythropoietic (congenital erythropoietic porphyria-CEP, erythropoietic/X-linked protoporphyria-EPP/XLP) or hepatic (acute hepatic porphyrias-AHPs, porphyria cutanea tarda-PCT), according to the site of organ dysfunction deemed to be responsible for the disease. In terms of total heme production, the liver accounts for the second major heme-synthesizing organ, after the bone marrow. In fact, heme is necessary as a prosthetic group in countless biologic functions, to which hepatic contribution is essential. Furthermore, the pathway of heme biosynthesis is inscribed into a network of fundamental metabolic reactions largely occurring in hepatocytes. Independent of their classification, all porphyrias share some degree of involvement of the liver, either in the pathogenesis, clinical manifestations, or as a preferential target of damage. Crucially, even those types of porphyrias that have been classically defined as erythropoietic do present a hepatic involvement, which can lead to poor clinical outcomes if neglected. Therefore, hepatologists should consider porphyrias as a differential diagnosis for otherwise unexplained presentations of liver disease. At the same time, a multidisciplinary team dealing with the diagnostic workup and clinical management of all types of porphyrias must include an expert in liver diseases. In this review, we aimed to recapitulate the main aspects of liver involvement in porphyrias, while also providing practical tools to recognize and manage these conditions from the hepatologist's perspective.