Congenital erythropoietic porphyria and erythropoietic protoporphyria: Identification of 7 uroporphyrinogen III synthase and 20 ferrochelatase novel mutations

The erythropoietic porphyrias are inborn errors of heme biosynthesis with prominent cutaneous manifestations. They include autosomal recessive Congenital Erythropoietic Porphyria (CEP) due to loss-of-function (LOF) mutations in the Uroporphyrinogen III Synthase (UROS) gene, Erythropoietic Protoporphyria (EPP) due to LOF mutations in the ferrochelatase (FECH) gene, and X-Linked Protoporphyria (XLP) due to gain-of-function mutations in the terminal exon of the Aminolevulinic Acid Synthase 2 (ALAS2) gene. During the 11-year period from 01/01/2007 through 12/31/2017, the Mount Sinai Porphyrias Diagnostic Laboratory provided molecular diagnostic testing for one or more of these disorders in 628 individuals, including 413 unrelated individuals. Of these 628, 120 patients were tested for CEP, 483 for EPP, and 331 for XLP, for a total of 934 tests. For CEP, 24 of 78 (31%) unrelated individuals tested had UROS mutations, including seven novel mutations. For EPP, 239 of 362 (66%) unrelated individuals tested had pathogenic FECH mutations, including twenty novel mutations. The IVS3-48 T > C low-expression allele was present in 231 (97%) of 239 mutation-positive EPP probands with a pathogenic FECH mutation. In the remaining 3%, three patients with two different FECH mutations in trans were identified. For XLP, 24 of 250 (10%) unrelated individuals tested had ALAS2 exon 11 mutations. No novel ALAS2 mutations were identified. Among family members referred for testing, 33 of 42 (79%) CEP, 62 of 121 (51%) EPP, and 31 of 81 (38%) XLP family members had the respective family mutation. Mutation-positive CEP, EPP, and XLP patients who had been biochemically tested had marked elevations of the disease-appropriate porphyrin intermediates. These results expand the molecular heterogeneity of the erythropoietic porphyrias by adding a total of 27 novel mutations. The results document the usefulness of molecular testing to confirm the positive biochemical findings in these patients and to identify heterozygous family members.