Porphyria Cutanea Tarda and Hepatoerythropoietic Porphyria: Identification of 19 Novel Uroporphyrinogen III Decarboxylase Mutations

Porphyria Cutanea Tarda (PCT) is a cutaneous porphyria that results from the hepatic inhibition of the heme biosynthetic enzyme uroporphyrinogen decarboxylase (UROD), and can occur either in the absence or presence of an inherited heterozygous UROD mutation (PCT subtypes 1 and 2, respectively). A heterozygous UROD mutation causes half-normal levels of UROD activity systemically, which is a susceptibility factor but is not sufficient alone to cause type 2 PCT. In both Types 1 and 2 PCT, the cutaneous manifestations are precipitated by additional factors that lead to generation of an inhibitor that more profoundly reduces hepatic UROD activity. PCT is an iron-related disorder, and many of its known susceptibility factors, which include infections (e.g. hepatitis C virus, HIV), high alcohol consumption, smoking, estrogens, and genetic traits (e.g. hemochromatosis mutations) can increase hepatic iron accumulation. Hepatoerythropoietic Porphyria (HEP) is a rare autosomal recessive disease that results from homozygosity or compound heterozygosity for UROD mutations and often causes infantile or childhood onset of both erythropoietic and cutaneous manifestations. During the 11-year period from 01/01/2007 through 12/31/2017, the Mount Sinai Porphyrias Diagnostic Laboratory provided molecular diagnostic testing for 387 unrelated patients with PCT and four unrelated patients with HEP. Of the 387 unrelated individuals tested for Type 2 PCT, 79 (20%) were heterozygous for UROD mutations. Among 26 family members of mutation-positive PCT patients, eight (31%) had the respective family mutation. Additionally, of the four unrelated HEP patients referred for UROD mutation analyses, all had homozygosity or compound heterozygosity for UROD mutations, and all eight asymptomatic family members were heterozygotes for UROD mutations. Of the UROD mutations identified, 19 were novel, including nine missense, two nonsense, one consensus splice-site, and seven insertions and deletions. These results expand the molecular heterogeneity of PCT and HEP by adding a total of 19 novel UROD mutations. Moreover, the results document the usefulness of molecular testing to confirm a genetic susceptibility trait in Type 2 PCT, confirm a diagnosis in HEP, and identify heterozygous family members.